Doctor of PhilosophyDoctor of Philosophyvinayakamission.com/userfiles/phd/O847600001.pdf · SALEM, TAMILNADU, INDIA MARCH 2014. SYNTHESIS, CHARACTERIZATION AND APPLICATION OF

SYNTHESIS, CHARACTERIZATION AND APPLICATIONS OF

NANO METAL OXIDES IN ENVIRONMENTAL REMEDIATION

Thesis submitted in

Partial Fulfillment for the award of the Degree

of

Doctor of PhilosophyDoctor of PhilosophyDoctor of PhilosophyDoctor of Philosophy

In Chemistry

By

JAHAGIRDAR ASHARAFKHAN ABDULRAHAMAN

(Registration Number: 0847600001)

Under the guidance of

Dr. N. DONAPPA

VINAYAKA MISSIONS UNIVERSITY

SALEM, TAMILNADU, INDIA

MARCH 2014

SYNTHESIS, CHARACTERIZATION AND APPLICATION OF

NANO METAL OXIDES IN ENVIRONMENTAL REMEDIATION

Thesis submitted in

Partial Fulfillment for the award of the Degree

of

Doctor of PhilosophyDoctor of PhilosophyDoctor of PhilosophyDoctor of Philosophy

In Chemistry

By

JAHAGIRDAR ASHARAFKHAN ABDULRAHAMAN

(Registration Number: 0847600001)

Under the guidance of

Dr. N. DONAPPA


SALEM, TAMILNADU, INDIA

APRIL 2014

Dedicated

To

My Beloved

Parents

x


DECLARATION

I, JAHAGIRDAR ASHARAFKHAN ABDULRAHAMAN declare

that the thesis entitled “SYNTHESIS, CHARACTERIZATION AND

APPLICATIONS OF NANO METAL OXIDES IN ENVIRONMENTAL

REMEDIATION” submitted by me for the Degree of Doctor of

Philosophy is the record of work carried out by me during the

period from October 2008 to April 2013 under the guidance of Dr.

N. DONAPPA and has not formed the basis for the award of any

degree, diploma, associate-ship, fellowship, titles in this or any other

University or institution of higher learning.

Place: Signature

Date:

xi


CERTIFICATE BY THE GUIDE

I, Dr. N. DONAPPA certify that the thesis entitled “SYNTHESIS,

CHARACTERIZATION AND APPLICATIONS OF NANO METAL

OXIDES IN ENVIRONMENTAL REMEDIATION” submitted for the

Degree Doctor of Philosophy by Mr. JAHAGIRDAR ASHARAFKHAN

ABDULRAHAMAN is the record of research work carried out by him

during the period from October 2008 to April 2013 under my guidance

and supervision and this work has not formed the basis for the award of

any degree, diploma, associate-ship, fellowship or other titles in this

University or any other University or institution of higher learning.

Place: Signature

Date:

i

A C K N O W L E D G E M E N T S

I express my sincere and heartfelt gratitude to my beloved and

esteemed research guide Dr. N Donappa, Professor, Department of

Chemistry Maharani Lakshmi Ammanni College for Women Bengalore. I

thank him whole heartedly for his consistent encouragement and imparting

valuable knowledge which led to the successful completion of my Ph.D.

program. I am also highly blessed to have a Mentor, Supervisor and a well-

wisher in the field of research.

It was a great privilege to work with Dr. B.M. Nagabhushana,

Department of Chemistry, MSRIT Bangalore. and Dr .H. Nagabhushana ,

P. G. Centre, Tumkur University, Tumkur for their encouragement, moral

support and innovative ideas which helped me to complete this program

successfully.

I am also thankful to Dr. RPS Chakradhar, Scientist, NAL for helping

in the EPR studies.

I express my deep & sincere gratitude to Prof. Dr. C.

Nanjundaswamy, Principal, Dr. Ambedkar Institute of Technology,

Bangalore, for timely help and encouragement.

I express my deep & sincere gratitude to the managements of Dr.

AIT, Bangalore and M S R I T Bangalore for providing needful support and

facilities.

ii

I would like to thank my well-wishers Dr. B Veenadevi Dr. V

Bheema Raju, , Smt. G V Jayashree, Dr. Dhananjaya, Dr. Umesh, Dr.

Shivakumar, Dr. Prem Kumar, Dr. P F Sanaulla, Mr. Jnaneshwar, Mr.

Harikrsihna, Mr. Madesh, Mr. Chandrashekar and Mr. Nagaraj for their

kind co-operation.

I would like to express my gratitude to Prof. K.C. Patil, Indian

Institute of Science for constant advice throughout the course of the work.

I would like to thank all the research scholars of MSRIT for their

help. I am highly grateful to Mr. Zulfiqar Ahmed M.N. for his keen interest

and timely help shown during the course of this work.

I am also thankful to the teaching and non-teaching staff of both Dr.

AIT and MSRIT for co-operation and support.

I thank all my family members for their continuous support, patience

and encouragement which has greatly helped me in completing the task in

a successful manner.

I also thank all those who have helped me in successful completion

of this research work.

Finally, I thank and render my sense of gratitude to the ALMIGHTY

GOD for showering his ceaseless blessings and giving me an opportunity

to explore the beauty of HIS wonderful world nanotechnology.

JAHAGIRDAR A. A.

i

TABLE OF CONTENTS

Section No.

TITLE Page No.

DECLARATION BY THE SCHOLAR DECLARATION BY THE GUIDE ACKNOWLEDGEMENTS TABLE OF CONTENTS i LIST OF PLATES viii LIST OF TABLES ix LIST OF FIGURES

LIST OF EQUATIONS xii xvi

CHAPTER 1 INTRODUCTION

1.1 Significance of water and its pollution 1 1.2 Nanotechnology and nanomaterials 3 1.3 Nano metal oxides 6 1.4 Nanocatalysis 7 1.5 Dye removal 9 1.6 Photocatalysis 14 1.7 Chemical oxygen demand 16 1.8 α-Fe2O3 nanoparticles 18 1.9 CeO2 nanoparticles 19 1.10 Preparation methods 20 1.11 Need for the study 21 1.12 Objectives of the present work 22

CHAPTER 2 REVIEW OF LITERATURE

2.1 Review of Literature 24

CHAPTER 3 SYNTHESIS OF THE NANO METAL OXIDES

3.1 Synthesis of the nano metal oxides 51 3.1.1 Hydrothermal method 51 3.1.2 Sol-gel method 52 3.1.3 Co-precipitation method 52 3.2 Solution combustion synthesis 53 3.2.1 Calculation of stoichiometry 57 3.2.2 Characteristics of solution combustion synthesis 60

ii

3.2.3 Role of fuels 61 3.2.4 General procedure for solution combustion

synthesis 63

3.2.5 Combustion chamber 67 3.3 Chemicals and reagents 67 3.4 Synthesis of α-Fe2O3 nanopowder by solution

combustion synthesis using ODH as fuel (NP1) 67

3.5 Synthesis of α-Fe2O3 nanopowder by solution combustion synthesis using Glycine as fuel (NP2)

69

3.6 Synthesis of CeO2 nanopowder by solution combustion synthesis using citric acid as fuel (NP3)

70

3.7 Concluding remarks 71

CHAPTER 4

CHARACTERIZATION OF THE NANO METAL OXIDES

4.1 Characterization techniques 72 4.2 X-ray diffraction studies 72 4.2.1 The Laue method 73 4.2.2 The rotating crystal method 73 4.2.3 The Debye-Scherer method 74 4.2.4 The Diffractometer method 74 4.2.5 Powder X-ray diffraction method 75 4.3 Fourier transform infrared spectroscopy 88 4.4 Scanning electron microscopy 93 4.5 UV-visible spectroscopy and band gap

measurements 96

4.5.1 Direct band gap 100 4.5.2 Indirect band gap 102 4.6 BET surface area 104 4.7 Concluding remarks 107

CHAPTER 5 PHOTOCATALYTIC ACTIVITY

5.1 Introduction 108 5.2 Electronic structure of a semiconductor 108 5.3 Mechanism of photocatalysis 108 5.4 Photoreactor and cell 111 5.5 General procedure for photocatalytic activity 112 5.6 Effect of variable factors 112 5.6.1 Effect of dosage of the photocatalyst 113

iii

5.6.2 Effect of irradiation time 113 5.7 Photocatalytic removal of methyl orange dye 114 5.7.1 Preparation of the dye solution 115 5.8 Photocatalytic removal of methyl orange dye by

NP1 115

5.8.1 Effect of dosage of the photocatalyst on the

removal of MO by NP1 116

5.8.2 Effect of irradiation time on the photocatalytic removal of MO by NP1

117

5.9 Photocatalytic removal of methyl orange dye by NP2

118

5.9.1 Effect of dosage of the photocatalyst on the removal of MO by NP2

118


119


121

5.10.1 Effect of dosage of the photocatalyst on the photocatalytic removal of MO by NP3

121


122

5.11 Photocatalytic removal of rhodamine B dye 123 5.11.1 Preparation of the dye solution 125 5.12 Photocatalytic removal of rhodamine B dye by

NP1 125

5.12.1 Effect of dosage of the photocatalyst on the

removal of RhB by NP1 125

5.12.2 Effect of irradiation time on the photocatalytic removal of RhB by NP1

127

5.13 Photocatalytic removal of rhodamine B dye by NP2

128

5.13.1 Effect of dosage of the photocatalyst on the removal of RhB by NP2

128


130


131

5.14.1 Effect of dosage of the photocatalyst on the removal of RhB by NP3

131


133

5.15 Photocatalytic removal of methylene blue dye 134 5.15.1 Preparation of the dye solution 136 5.16 Photocatalytic removal of methylene blue dye

by NP1 136

5.16.1 Effect of dosage of the photocatalyst on the 136

iv

removal of MB by NP1 5.16.2 Effect of irradiation time on the photocatalytic

removal of MB by NP1 138

5.17 Photocatalytic removal of methylene blue dye by NP2

139

5.17.1 Effect of dosage of the photocatalyst on the removal of MB by NP2

139

5.17.2 Effect of irradiation time on the photocatalytic removal of MB by NP2

140


142

5.18.1 Effect of dosage of the photocatalyst on the removal of MB by NP3

142

5.18.2 Effect of irradiation time on the photocatalytic removal of MB by NP3

143

5.19 Regeneration of the photocatalysts 145 5.20 Photocatalytic removal of methyl orange dye by

RNP1 146

5.20.1 Effect of dosage of the photocatalyst on the removal of MO by RNP1

146

5.20.2 Effect of irradiation time on the photocatalytic removal of MO by RNP1

147

5.21 Photocatalytic removal of methyl orange dye by RNP2

149


149


150


152


152


153

5.23 Photocatalytic removal of rhodamine B dye by RNP1

155

5.23.1 Effect of dosage of the photocatalyst on the removal of RhB by RNP1

155

5.23.2 Effect of irradiation time on the photocatalytic removal of RhB by RNP1

156


158


158


159

v


161


161


162

5.26 Photocatalytic removal of methylene blue dye by RNP1

164

5.26.1 Effect of dosage of the photocatalyst on the removal of MB by RNP1

164

5.26.2 Effect of irradiation time on the photocatalytic removal of MB by RNP1

165


167


167


168


170


170


171


CHAPTER 6 REDUCTION IN CHEMICAL OXYGEN DEMAND (COD) OF AN INDUSTRIAL

EFFLUENT

6.1 Chemical oxygen demand 174 6.2 Study area – The Vrishbhavathi River 175 6.2.1 Sampling and analysis 179 6.2.2 Sample preservation 180 6.3 Open reflux method for the determination of

COD 180

6.3.1 Chemicals and reagents 181 6.3.2 Preparation of the reagents 181 6.3.3 Determination of COD of the effluent sample

without the nanopowder 182

6.3.4 Determination of COD of the effluent sample with the nanopowder

184

6.4 Reduction in COD of the industrial effluent by NP1

186

6.4.1 Effect of dosage of the nanopowder on the 186

vi

reduction in COD of the industrial effluent by NP1

6.4.2 Effect of contact time on the reduction in COD of the industrial effluent by NP1

188


189

6.5.1 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP2

189


191


192

6.6.1 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP3

192


193

6.7 Regeneration of the nanopowders 195 6.8 Reduction in COD of the industrial effluent by

RNP1 196

6.8.1 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by RNP1

196

6.8.2 Effect of contact time on the reduction in COD of the industrial effluent by RNP1

197

6.9 Reduction in COD of the industrial effluent by RNP2

199


199


201

6.10 Reduction in COD of the industrial effluent by RNP3

202


202


204


CHAPTER 7

CONCLUSIONS

207

vii

CHAPTER 8

REFERENCES

209

SCOPE FOR FUTURE WORK

LIST OF PAPERS PUBLISHED

viii

LIST OF PLATES

Plate no. Plate Caption Page no.

3.1 Redox mixture stirred on a magnetic stirrer 65

3.2 Redox mixture introduced into the muffle furnace

65

3.3 Ignition of the redox mixture 66

3.4 Combustion of the redox mixture 66

6.1 The Vrishbhavathi River (Photo 1) 177




6.5 The COD digester 181

ix

LIST OF TABLES

Table no.

Table Caption Page no.

4.1 Rietveld refined structural parameters for nanopowder NP1

85


87


88

4.4 Band gap energy values of the three nanopowders

104

4.5 BET surface area values of the three nanopowders

106

5.1 Effect of dosage of the photocatalyst on the photocatalytic removal of MO by NP1

116

5.2 Effect of irradiation time on the photocatalytic removal of MO by NP1

117


118


120


121


123

5.7 Effect of dosage of the photocatalyst on the photocatalytic removal of RhB by NP1

126

5.8 Effect of irradiation time on the photocatalytic removal of RhB by NP1

127


129


130


132


133

5.13 Effect of dosage of the photocatalyst on the photocatalytic removal of MB by NP1

137

x

5.14 Effect of irradiation time on the photocatalytic removal of MB by NP1

138


140


141


142


144

5.19 Codes of the photocatalysts before and after regeneration

145

5.20 Effect of dosage of the photocatalyst on the photocatalytic removal of MO by RNP1

146

5.21 Effect of irradiation time on the photocatalytic removal of MO by RNP1

148


149


151


152


154

5.26 Effect of dosage of the photocatalyst on the photocatalytic removal of RhB by RNP1

155

5.27 Effect of irradiation time on the photocatalytic removal of RhB by RNP1

157


158


160


161


163

5.32 Effect of dosage of the photocatalyst on the photocatalytic removal of MB by RNP1

164

5.33 Effect of irradiation time on the photocatalytic removal of MB by RNP1

166


167

xi


169


170


172

6.1 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP1

187

6.2 Effect of contact time on the reduction in COD of the industrial effluent by NP1

188


190


191


193


194

6.7 Codes of the nanopowders before and after regeneration

196

6.8 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by RNP1

197

6.9 Effect of contact time on the reduction in COD of the industrial effluent by RNP1

198


200


201


202


204

xii

LIST OF FIGURES Figure no.

Figure Caption Page no.

3.1 The Fire Triangle 54 4.1 Scheme for the derivation of Bragg's law 76 4.2 Schematic diagram of the setup for PXRD 77 4.3 PXRD pattern of the nanopowder NP1 79 4.4 PXRD pattern of the nanopowder NP2 80 4.5 PXRD pattern of the nanopowder NP3 81 4.6 W-H plot of the nanopowder NP1 82 4.7 W-H plot of the nanopowder NP2 82 4.8 W-H plot of the nanopowder NP3 83 4.9 Rietveld analysis of the nanopowder NP1 84 4.10 Packing diagram of the nanopowder NP1 85 4.11 Rietveld analysis of the nanopowder NP2 86 4.12 Packing diagram of the nanopowder NP2 86 4.13 Rietveld analysis of the nanopowder NP3 87 4.14 Packing diagram of the nanopowder NP3 88 4.15 FTIR spectrum of the nanopowder NP1 91 4.16 FTIR spectrum of the nanopowder NP2 92 4.17 FTIR spectrum of the nanopowder NP3 92 4.18 SEM micrograph of the nanopowder NP1 94 4.19 SEM micrograph of the nanopowder NP2 95 4.20 SEM micrograph of the nanopowder NP3 95 4.21 UV–Visible spectrum of the nanopowder NP1 98 4.22 UV–Visible spectrum of the nanopowder NP2 99 4.23 UV–Visible spectrum of the nanopowder NP3 100 4.24 Direct band gap of the nanopowder NP1 101 4.25 Direct band gap of the nanopowder NP2 101 4.26 Direct band gap of the nanopowder NP3 102 4.27 Indirect band gap of the nanopowder NP1 103 4.28 Indirect band gap of the nanopowder NP2 103 4.29 Indirect band gap of the nanopowder NP3 104 4.30 BET surface area of the nanopowder NP1 105 4.31 BET surface area of the nanopowder NP2 106 4.32 BET surface area of the nanopowder NP3 106 5.1 Mechanism of photocatalysis 109 5.2 Structure of methyl orange dye 114 5.3 Absorbance spectrum of methyl orange dye 115 5.4 Effect of dosage photocatalyst on the

photocatalytic removal of MO by NP1 116

xiii


118

5.6 Effect of dosage photocatalyst on the photocatalytic removal of MO by NP2

119


120

5.8 Effect of dosage photocatalyst on the photocatalytic removal of MO by NP3

122


123

5.10 Structure of rhodamine B dye 124 5.11 Absorbance spectrum of rhodamine B dye 125 5.12 Effect of dosage of photocatalyst on the

photocatalytic removal of RhB by NP1 126

5.13 Effect of irradiation time on the photocatalytic removal of RhB dye by NP1

128

5.14 Effect of dosage of photocatalyst on the photocatalytic removal of RhB by NP2

129


131

5.16 Effect of dosage of photocatalyst on the photocatalytic removal of RhB by NP3

132


134

5.18 Structure of methylene blue dye 135 5.19 Absorbance spectrum of methylene blue dye 135 5.20 Effect of dosage of photocatalyst on the

photocatalytic removal of MB dye by NP1 137


139

5.22 Effect of dosage of photocatalyst on the photocatalytic removal of MB dye by NP2

140


141

5.24 Effect of dosage of photocatalyst on the photocatalytic removal of MB dye by NP3

143


144

5.26 Effect of dosage photocatalyst on the photocatalytic removal of MO by RNP1

147


148

5.28 Effect of dosage photocatalyst on the 150

xiv

photocatalytic removal of MO by RNP2 5.29 Effect of irradiation time on the photocatalytic

removal of MO by RNP2 151

5.30 Effect of dosage photocatalyst on the photocatalytic removal of MO by RNP3

153


154

5.32 Effect of dosage of photocatalyst on the photocatalytic removal of RhB by RNP1

156

5.33 Effect of irradiation time on the photocatalytic removal of RhB dye by RNP1

157


159


160


162


163

5.38 Effect of dosage of photocatalyst on the photocatalytic removal of MB dye by RNP1

165


166


168


169


171


172


187


189


190


192

6.5 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by

193

xv

NP3 6.6 Effect of contact time on the reduction in

COD of the industrial effluent by NP3 195


197


199


200


202


203


205

xvi

LIST OF EQUATIONS Equation no.

Page no.

1.1 16 1.2 16 1.3 16 1.4 16

3.1 57

3.2 58

3.3 59

3.4 68

3.5 70

3.6 71

4.1 75

4.2 75

4.3 76

4.4 78

4.5 78

4.6 81

4.7 100

4.8 102

5.1 110

5.2 110

5.3 110

5.4 110

5.5 110

5.6 110

5.7 110

5.8 112 6.1 184

6.2 185

xvii

CHAPTER 1

INTRODUCTION

1

1.1 Significance of water and its pollution

Water is one of the important constituents and fundamental

requirements of life required for the survival of living beings. It is one of

the precious gifts of nature. Water used for various purposes must be

free from various types of pollutants and pathogens. The presence of

these pollutants in water causes health hazards. Clean water is not

only essential to human health, but is also a critical feedstock in

different industries including electronics, pharmaceuticals and food.

The addition of any undesirable chemical substances to water

results in its contamination and makes it unfit not only for human

consumption but also for other living beings. Clean water is not only

essential for the survival of living beings but is also a critical feedstock

for a number of industries. In addition to this, agricultural production

mainly relies on the availability of clean water. Water usually contains

some amount of physical, chemical and biological impurities. The

quality of water is defined by the level of physical, chemical and

biological impurities present in it. The water quality affects the health of

living organisms since a number of diseases are caused due to the toxic

chemicals and pathogens transmitted by water.

The physical properties of water include color, turbidity, taste,

temperature, pH and electrical conductivity. The chemical constituents

include dissolved salts, dissolved gases, organic matter etc. It has been

reported that all activities carried out on the land surface have the

2

potential to pollute water. These activities may be associated with

urban, industrial or agricultural land uses.

It is well known that industries consume large quantities of water

for different industrial processes. However, only a small fraction of the

same is incorporated in their products and lost by evaporation. The rest

finds its way into the water bodies as waste water. The industrial wastes

either join the streams or other natural bodies either directly or are

emptied into the municipal sewers. Hence these wastes in some way or

the other affect the normal life of a stream or the normal functioning of a

sewerage and sewage treatment plant. The main cause for the

contamination of surface and ground water is the discharge from

industries. The characteristics of industrial wastes vary not only with the

type of industry but also from plant to plant producing same type of end

products.

The pollutants from industries can be classified as follows:

(i) Organic compounds that deplete the oxygen content of the

receiving streams.

(ii) Inorganic compounds like carbonates, chlorides, nitrogen etc. that

make the water unfit for use.

(iii) Acids or alkalis that make the receiving stream unsuitable for the

growth of fish and other aquatic organisms.

(iv) Toxic substances such as cyanides, sulphides, acetylene,

alcohols, petrol etc. that cause damage to the flora and fauna of the

3

receiving streams and also sometimes, endanger the safety of the

workmen.

(v) Colour producing substances such as dyes which impart colour

and sometimes release carcinogenic substances into the water.

(vi) Oil and floating substances which interfere in the self purification

process of the streams.

The pollutants can be broadly classified as biodegradable and non-

biodegradable. The biodegradable substances can be broken down to

harmless products. The removal of non- biodegradable organic

chemicals is one of the challenging tasks of the environmental scientists

[1].

1.2 Nanotechnology and Nanomaterials

In 1959, Nobel Prize winner, physicist Richard P. Feynman said in

his famous speech: “There is plenty of room at the bottom.” Now, when

one looks back at this age, one will wonder why it was not until the year

1960 that anybody began seriously to move in this (nanometer)

direction.

Actually, in the years after, people did want to move in this direction”.

However, not much progress was made in both nanoscience and

nanotechnology until 1980’s when scanning tunneling microscope

(STM) was invented. This is because there were not many suitable

analytical tools available to investigate nanometer scale materials. After

4

STM, highly advanced analytical tools were developed (and are still

developed) rapidly, which enable the characterization and manipulation

of small objects down to a few nanometers bringing human being’s view

into the real atomic world. As one of the consequences of explosive

development of nanoscience, nanotechnology had its breakthrough

before the coming of the new century. Nowadays, many remarkable

techniques, such as nanoimprint lithography, self-assembly technique,

nanoscale crystal growth technique are already available to make

nanoscale products in relatively large amounts, showing the great

potentials of nanotechnology in real applications.

Nanotechnology has dramatically changed every aspect of the way

that we think in science and technology and will definitely bring more

and more surprises into our daily life as well as in the world in future.

The term “Nano” refers to one billionth (10−9

) of a meter. That is, 1

nanometer refers to 10−9

meter and is expressed as 1 nm. 1 nanometer

is so small that things smaller than it can only be molecules, clusters of

atoms or particles in the quantum world. Nanometer is a special point in

the overall length scale because nanometer scale is the junction where

the smallest manufacturable objects meet the largest molecules in

nature. When matter is arranged by exercising control over lengths of 1

to 100 nanometers and the formulating structures exhibit characteristics

that are specific to their size and dimensions, the resulting materials are

termed as nanomaterials. These structures, devices and systems have

5

at least one dimension in nanometer scale and are not only smaller than

anything that we have ever made before, but also possibly the smallest

solid materials that we are able to produce. Besides, in nanometer

scale, the properties of materials that we are familiar with in our daily

life, such as color, melting point, electronic, catalytic or magnetic

properties will change dramatically or be replaced by completely novel

properties due to what is usually called the size effect. At this size scale,

everything, regardless of what it is, has new properties.

Nanomaterials are materials with structural features of at least one

dimension in the range of 1-100 nm. These materials are notable for

their extremely small particle size or crystalline grain size and have the

potential for wide ranging industrial, biomedical, and electronic

applications. They can be metals, ceramics, polymeric or composite

materials. These nanomaterials possess unique chemical, physical,

optical and mechanical properties and hence are useful as sensors,

catalysts, coating materials (modifiers of surface properties) and

miniaturization of devices (integrated chips).

Although nanomaterials represent a large variety of materials in the

domain of nanometers, nanoparticles are always being considered as

one of a few core materials in nanoscience and nanotechnology. This is

because in addition to the small size, nanoparticles represent the most

popular morphology of the nanoscale world and are ideal manipulable

building blocks to construct larger devices, structures and systems

6

following the so-called “bottom-up” approach in nanotechnology. Many

discoveries related to nanoparticle synthesis, such as the discovery of

carbon nanotubes, the synthesis of well defined quantum dots or the

shape control of CeSe nanocrystals can be regarded as milestones in

the history of nanoscience which further proves the important role of

nanoparticles in nanoscience [2-4].

1.3 Nano metal oxides

Nano metal oxides constitute an important class of inorganic

nanomaterials. Metal oxides exhibit optical, electrical, magnetic,

mechanical and catalytic properties. These properties make them

technologically useful particularly in the field of material science. The

physical and chemical properties of oxide materials are greatly

influenced by their structure and this relation has a great significance.

MgO, CaO and ZnO are used as adsorbents in defluoridation, COD and

color removal from drinking water and industrial effluents.

Nano metal oxides have large surface area to volume ratio which

makes them efficient catalysts. They possess excellent sintering

characteristics and hence are widely used in the manufacture of

ceramics and composites. Dispersion of various fluids leads to

fabrication of corrosion resistant coatings and thin films. Currently, the

attention of many researchers across different parts of the globe is

focussed on the study of nanocrystalline metal oxides. It is a known and

7

accepted fact that a decrease in size of particles leads to remarkable

variations in the properties of materials [5].

Some of these are as follows:

(i) Increase in catalytic activity.

(ii) Increase in mechanical reinforcement.

(iii) Increase in electrical conductivity in ceramics.

(iv) Decrease in conductivity of metals.

(v) Increase in photocatalytic activity.

(vi) Increase in luminescence of semiconductors.

(vii) Super paramagnetic behaviour of magnetic oxides, to name a few.

1.4 Nanocatalysis

Homogeneous catalysts are most active with many attractive

properties such as high chemical and regioselectivities and also high

activities. However, engineering processes involving homogeneous

catalysis suffer from various difficulties. These include cumbersome

product purification, difficulty of catalyst recovery, deactivation via the

aggregation of metal nanoparticles formed in-situ during the reaction.

As a result of these drawbacks, many efficient systems cannot be

commercialized.

Heterogeneous catalysis is one of the best options to overcome

the difficulties encountered in homogeneous catalysis. Here the

catalysts have excellent stability, are easily accessible and can be

8

easily separated from the reaction mixture. However, they do have

some drawbacks. First, inferior catalytic performance relative to their

homogeneous counterparts, because of reduced contacts between the

catalyst and the substrate and second is the use of filtration to isolate

the catalyst from reaction mixture, which reduces the efficiency of the

system at each cycle.

In view of this, there is a need for a new catalytic system, which

should be efficient like homogeneous catalysis and the catalyst should

be easily recoverable like heterogeneous catalyst. Nanocatalysis can be

considered as a bridge between homogeneous and heterogeneous

catalytic systems. This is recently attracting the attention of many

researchers across the globe. Because of the small size and high

surface area of the nanocatalyst, the contact between reactants and

catalyst increases dramatically and it can operate in the same manner

as homogeneous catalyst (close to homogeneous catalysis). At the

same time, due to its insolubility in the reaction solvent, the

nanocatalyst can be separated easily from the reaction mixture. Thus,

nanocatalysts can combine the advantages of both homogeneous and

heterogeneous catalysts and can offer unique activity with high

selectivity.

In nanocatalysis, nano particles are used to catalyze reactions.

The catalysis can be homogeneous or heterogeneous. At nano level,

the particles have larger surface area to volume ratio compared to that

9

in the bulk materials. The reduction in size results in the involvement of

a large number of atoms in the catalysis process. These properties

make the nano particles attractive catalysts. The surface atoms can

occupy the corners and edges of the nano particles and thus become

chemically unsaturated and also much more active. The smaller size

increases the activity of the surface atoms and leads to surface

reconstruction [6].

1.5 Dye removal

A dye can generally be described as a colored substance that has

an affinity to the substrate on which it is being applied. The dye is

generally applied in an aqueous solution and may require a mordant to

improve its fastness on the fiber. Since antiquity, fabrics have been

dyed with extracts from minerals, plants, and animals. In fact, dyeing

historically was a secretive art form and the most beautiful and exotic

pigments were reserved only for those who had the status to wear

them. Things began to change around 1856 when scientists discovered

how to make synthetic dyes. Cheaper to produce, brighter, more color-

fast, and easy to apply to fabric, these new dyes changed the playing

field. Scientists raced to formulate gorgeous new colours and before

long, dyed fabrics were available to all, the natural dyes had become

obsolete for most applications [7, 8].

10

Constant research done over the 20th century and thereafter has

resulted into every imaginable form of color of dye. Modern dyes serve

more than just being pretty. These dyes have become indispensable

tools for a variety of industries. From acting as colorants for plastics,

textile dyeing industries and the highly sophisticated biotechnology

industry, dyes are touching our life everywhere. Dyes are also used by

industries for inks and tinting. Today various dyes are manufactured to

meet the requirements of different types of industries. These dyes are

available in various forms such as dry powders, granules, pastes,

liquids, pellets, and chips. Other industries that use the dyes in a variety

of products include paper and pulp, adhesives, art supplies, beverages,

ceramics, construction, cosmetics, food, glass, paints, waxes, polymers,

soaps, biomedicines etc.

Dyes that cater to the needs of different industries often come with

specialized properties that include the following:

(i) Resistance to heat and resistance to weather conditions.

(ii) Resistance to ultraviolet light (UV).

(iii) Some products are water soluble.

(iv) Electrical conductivity.

(v) Contain reinforcing fibers.

(vi) Free from heavy metals.

Over 100,000 commercially available dyes exist and their annual

production exceeds 7 x 105 tonnes. However, this brightly coloured,

11

changed new world is not without a down side. The chemicals used to

produce dyes today are often highly toxic, carcinogenic or even

explosive. The chemical aniline, the basis for a popular group of dyes

known as azo dyes (which are considered deadly poisons giving off

carcinogenic amines) is dangerous to work with due to toxicity and

highly inflammable properties [9]. In addition to this, some of the other

harmful chemicals used in the dyeing process include:

(i) Dioxin – a carcinogen and possible hormone disrupter.

(ii) Toxic heavy metals such as chromium, copper, and zinc which

are associated with carcinogenic effects and other health hazards, and

(iii) Formaldehyde, a suspected carcinogen.

It is apparent that there are deadly risks to workers who are

involved in the manufacture of dyes and dyeing of garments. Dye

workers are at higher risk of tumors, cancers, cerebrovascular diseases

and lung diseases. Almost every industrial dye process involves a

solution of a dye in water, in which the fabrics are dipped or washed.

After dyeing a batch of fabric, it is cheaper to dump the used water (dye

effluent) than to clean and reuse it. It is due to this fact that many of the

dyeing industries across the world are dumping millions of tons of dye

effluents into the rivers. Most of the dyes are readily soluble in water

and are also quiet stable. As a result of this extra stability, these dyes

ultimately find their way into the aquatic ecosystem and have adverse

and sometimes irreversible effects on both animals and plants. Some of

12

the dye effluents are known to release potentially harmful and

carcinogenic substances into the water which poses a serious threat to

aquatic living organisms. Apart from being carcinogenic, these dyes are

known to have adverse effects on mankind including malfunctioning of

kidneys, lungs, intestine, liver etc. These dyes inhibit the penetration of

light into the water leading to the death of phytoplankton. It is very

difficult to treat the waste water containing these dyes because of the

fact that these dyes are recalcitrant organic molecules, resistant to

aerobic digestion and are stable to light, heat and oxidizing agents [10].

Dyes are so problematic because the families of chemical

compounds that make good dyes are also toxic to human beings. Each

of the newly developed dye is a brand new compound and because it is

new, no one knows its risks to living beings and the environment. The

textile industry has a big pollution problem. The World Bank estimates

that 17 to 20 percent of the industrial water pollution comes from textile

dyeing and treatment. They have also identified 72 toxic chemicals in

effluent water solely from textile dyeing, 30 of which cannot be

removed. This presents an appalling environmental problem for the

fabric designers and other textile manufacturers.

The pulp and paper industries manufacture papers and similar

products. It is also one of the industries contributing towards pollution of

water. The wastewater from the pulp and paper industry

characteristically contains very high COD and color. The presence of

13

lignin in the waste which is derived from the raw cellulosic materials

makes the COD/BOD ratio of the waste very high. Apart from this the

textile mills also utilize pulp for making rayon fabrics. In order to get

different shades of colors to the papers and textiles, different types of

dyes are being used. The presence of these dyes also increases the

COD of the effluent and causes a number of aesthetic problems. This

limits the possible use of water and reduces the efficiency of microbial

waste water treatment since some of the dyes are harmful to the

microorganisms themselves.

Azo dyes which contain one or more nitrogen to nitrogen double

bond (–N=N–) are of much greater significance. The products of

degradation of these azo dyes can be mutagenic and carcinogenic

causing long term health effects. These azo dyes do not undergo

biodegradation by aerobic treatment processes. Under anaerobic

conditions, they are reduced to potentially carcinogenic aromatic

amines [11, 12]. This has attracted the attention of many researchers

across the world to find solutions to remove the dyes and reduce the

chemical oxygen demand (COD) levels of effluent water from industries.

In view of these adverse effects, the industrial effluents containing

dyes have to be treated so that they are free from these dyes. The

conventional methods employed to remove dyes from water bodies

include precipitation, adsorption, air stripping, flocculation, reverse

osmosis, ultrafiltration etc. Many of these methods suffer from various

14

drawbacks. The conventional biological methods used for the treatment

of industrial waste water are ineffective resulting in an intensely colored

discharge from the treatment facilities [13-15].

1.6 Photocatalysis

A photocatalyst is a substance which exhibits catalytic activity in

the presence of light and the phenomenon is referred to as

photocatalysis. Heterogeneous photocatalysis using nano

semiconductor metal oxides is a promising technology for the reduction

of global environmental pollutants. The treatment of colored waste

water not only involves its decolorization, but also its detoxification. The

main goal of heterogeneous photocatalysis is complete mineralization of

pollutants into harmless compounds. In some cases, complete

mineralization of organic matter to carbon dioxide and mineral acids has

been achieved. It is one of the advanced techniques coupling ultraviolet

light or sunlight with nano materials as photocatalysts [16-18].

Some of the important conditions for a substance to exhibit

efficient photocatalytic properties have been discussed as follows. The

chemical elements making up the semiconducting material should be

capable of reversibly changing its valence state to accommodate a hole

without decomposing the semiconductor. It should not have just one

stable valence state in the semiconductor material. The semiconductor

15

should have suitable band gap energy (Eg), stable towards

photocorrosion, non-toxic in nature and less expensive. It should also

possess physical and chemical properties that enable it to act as a

catalyst. Metal oxide semiconductors have been recognized as effective

photocatalysts for the degradation of a number of organic pollutants

such as azo-dyes and phenol derivatives. These organic compounds

get adsorbed onto the catalyst surface and are then mineralized into

carbon dioxide and water through a redox reaction brought about by

hydroxyl or superoxide radicals. The photocatalytic process is known to

occur at the surface or within a few monolayers around the catalyst

particles. Transition metal oxides are being widely used as

photocatalysts for the degradation of a number of azo-dyes [19, 20].

Nano metal oxides such as TiO2, ZnO, CeO2, ZrO2, Fe2O3, CaO,

MgO, WO3 etc. have been extensively studied as photocatalysts for the

degradation of a number of dyes and various organic and inorganic

pollutants [21, 22].

The possible mechanism of photocatalysis by these nano metal

oxides is as follows. When ultraviolet radiation is used in the

photocatalytic reaction, the electrons in the photocatalyst are excited

from the valence band to the conduction band by absorption of energy

photons leaving positive holes in the valence band. The electrons in the

conduction band react with the adsorbed oxygen molecules to form O2-

16

species, while the positive holes react with the adsorbed hydroxyl ions

to form hydroxyl radicals.

In case of Fe2O3 nanocatalyst, these processes can be

represented as follows (Equations 1.1 to 1.3):

Fe2O3 + hυ (energy ~ 2.3 eV) e— + h+ ..... (1.1)

e— + O2 (ads) O2— (ads) ..... (1.2)

h+ + OH— •OH (s) ..... (1.3)

The hydroxyl radicals are highly reactive and combine with the dye

molecules, thus degrading them (Equation 1.4).

•OH + dye degradation products ..... (1.4)

1.7 Chemical oxygen demand

For several years, the water bodies such as rivers, lakes and sea

received urban and industrial wastewater without any treatment. The

majority of this wastewater was not subjected to any previous treatment

before its discharge into the water bodies. This has resulted in the

deterioration of the water bodies contributing to water pollution. The

water pollution can chemical, organic or physical [23]. In many several

cases, the industries are not equipped with sewage treatment plants. As

a result, majority of the industrial effluents are directly discharged into

the water bodies without any limit of norms [24].

The chemical oxygen demand (COD) is a measure of the oxygen

equivalent of the organic matter content of a sample that is susceptible

17

to oxidation by a strong oxidizing agent such as potassium dichromate.

In some cases, for samples from a particular source, the COD can be

related empirically to the biochemical oxygen demand (BOD), organic

carbon or organic matter. The wastewater generated from different

types of industries is highly polluting because it contains high

biochemical oxygen demand (BOD), chemical oxygen demand (COD),

toxic substances, recalcitrant organic compounds and coloring matter

such as dyes and pigments. The industries generally employ primary

physicochemical treatment followed by secondary treatment, such as

wet air oxidation, incineration or biological treatment.

The textile industry is one of the major industries that produce a

large volume of wastewater. The major problem of the textile waste

effluent is the strong colour. The wastewater from the cotton textile mill

usually possesses high values of BOD, COD, color and pH. The

discharge of such waste water into the receiving waters causes severe

damage to the environment [25, 26].

The industries are one of the major sources of contaminants for

the aquatic environments by atmospheric deposition and wastewater

discharge. The pulp and paper industry, oil, cement, leather, textile, and

steel industries discharge different types of gaseous, liquid, and solid

wastes into the environment. The pollution of water bodies is one of the

major challenges to the environmental engineers due to the large

volumes of wastewater generated by the industries. The pollutants

18

present in these industrial effluents depend on the nature of the raw

material, the finished product and the extent of water reuse. For

example, in case of paper and textile industries, the pulp produced

corresponds to only about 40 to 45% of the original weight of the wood.

As a result, the effluents are heavily loaded with the organic matter.

These effluents have high values of both BOD and COD. If they are

discharged directly into the receiving waters without treatment, they

cause severe damage to the aquatic environment. The chlorinated

compounds are measured as adsorbable organic halides.

1.8 α-Fe2O3 nanoparticles

α-Fe2O3 nanoparticles have attracted the attention of researchers

working in the fields of nanoscience and nanotechnology due to their

unique characteristics such as superparamagnetism, high saturation

fields and extra anisotropy contributions. These characteristics arise

from the effects of finite size and large surface area and make them

highly useful in many areas such as magnetism, catalysis,

electrochemistry, biotechnology, photocatalysis, lithium ion battery etc.

For example, it is one of the frequently used catalysts in the chemical

industry and can also be used in gas sensors to detect combustible

gases such as CH4, C3H8 and C4H8.

α-Fe2O3 is highly stable iron oxide possessing n-type

semiconducting properties having a band gap of around 2.1 eV at

19

ambient conditions. Microwave assisted synthesized α-Fe2O3

nanoparticles have been used in humidity sensors. Nanocrystalline α-

Fe2O3 synthesized by solution combustion synthesis has been used as

adsorbent for the removal of the dye indacid millingred. The

photocatalytic activity of α-Fe2O3 for removal of a number of dyes has

been reported in literature [27-29].

1.9 CeO2 nanoparticles

Nanocrystalline CeO2 is being proposed as a redox mediator for

the modification of conventional electrodes used in electro-analytical

techniques and as photocatalyst for the degradation of dyes. As a result

of its high specific surface area, CeO2 can promote electron transfer

reactions at a lower potential. It has good electrochemical activity and

wide range of applications in a number of fields such as catalysis, fuel

cells, and sensors. CeO2 plays an important role in emerging

technologies for environmental applications. CeO2 absorbs radiation in

the near UV region and also little amount of visible light. As a result, it

absorbs larger fraction of the solar spectrum than TiO2. CeO2 containing

materials can be used as efficient oxidation catalysts, because CeO2

has unique redox property and high oxygen storage capacity (OSC). It

is regarded an environmental friendly catalyst for the destruction of

various volatile organic compounds (VOCs) such as methane, methanol

and propane [30].

20

1.10 Preparation methods

Various techniques are available for the preparation of

nanomaterials. Some of these methods are co-precipitation, sol-gel and

hydrothermal, solvothermal etc., [31, 32]. These methods suffer from

various drawbacks such as long processing time, costly chemicals,

special experimental set up, long sintering or annealing process, high

temperature etc., [33-35].

Solution combustion synthesis is regarded as a versatile method

for the preparation of a large number of nano metal oxides. In solution

combustion synthesis, an aqueous redox mixture containing

stoichiometric amounts of the metal nitrate (oxidizer) and fuel is heated

on a hot plate to evaporate the excess water and then introduced into a

muffle furnace maintained at around 300 ± 50˚C. The reaction mixture

first undergoes dehydration and then ignites instantaneously at one

point. The combustion process propagates throughout the reaction

mixture and the nano metal oxide is formed as a porous fluffy powder.

All metal nitrates on pyrolysis yield corresponding metal oxides.

The decomposition temperature of the metal nitrates can be lowered by

the addition of the fuel. The choice of fuel is critical in deciding the

exothermicity of the redox reaction between the metal nitrate and the

fuel. Depending upon the exothermicity of the reaction, the combustion

reaction can be smoldering, flaming or explosive in nature.

21

The combustion reaction is influenced by the type of fuel used

and the fuel to oxidizer ratio. The reaction is exothermic and the

temperature of the reaction varies from 1000 0C to 1500 0C. Some of

the fuels are found to be specific for a particular class of compounds.

For example, urea is specific for alumina and related oxides,

carbhydrazide (CH) for zirconia and related oxides, oxalyldihydrazide

(ODH) for Fe2O3 and ferrites, tetraformaltrisazine (TFTA) for titania and

realted oxides, Glycine for chromium and related oxides etc.

Solution combustion process has several advantages such as

fast heating rates and short reaction time, besides producing porous,

foamy and high surface area nanomaterials. It is a versatile process to

synthesize single phase composites, solid solutions as well as complex

compound oxide phases in homogeneous form [36].

In the present work, nano metal oxides were synthesized by

solution combustion method. The synthesized nano metal oxides were

used for the removal of three dyes, viz., methyl orange, rhodamine B

and methylene blue from their aqueous solutions. The nano metal

oxides were also used in the reduction of COD of the industrial effluent

collected from the Vrishbhavathi River of Bangalore, India.

1.11 Need for the study

Water is a vital source of life on earth. With the increase in

population, industrialization and urbanization; problems related to

22

shortage, misuse and pollution of water are widespread. Clean water is

a requirement for proper functioning of society. While water is plentiful,

clean water for human consumption is often limited. Various methods

such as adsorption, flocculation, activated sludge process, filtration,

Fenton’s process etc. are being employed for the removal of pollutants

from water. These methods suffer from drawbacks such as lesser

efficiency, slow rate of removal of pollutants, production of secondary

pollutants etc. Hence there is a need for more efficient and economical

methods for the removal of pollutants from water.

In recent years, there has been growing interest in applications of

nano metal oxides as adsorbents and photocatalysts in removal of

various pollutants from waste water.

1.12 Objectives of the present work

The work was started with the following objectives:

(i) To synthesize three nano metal oxides viz. α-Fe2O3 using oxalyl

dihydrazide as fuel; α-Fe2O3 using Glycine as fuel and CeO2 using citric

acid as fuel by solution combustion synthesis. The products were

designated as NP1, NP2 and NP3 respectively.

(ii) To characterize the as-prepared nano metal oxides by PXRD,

FTIR, SEM, UV-Visible spectroscopy, band gap and BET surface area

measurements.

23

(iii) To study the photocatalytic activity of the three nano metal

oxides for the removal of methyl orange, rhodamine B and methylene

blue dyes from their aqueous solutions.

(iv) To study the efficiency of the three nano metal oxides in the

reduction in COD of the industrial effluent from Vrishbhavathi River of

Bangalore, India.

(v) To study the effect of regeneration on the efficiency of the nano

metal oxides in the photocatalytic removal of the three dyes and

reduction in COD of the industrial effluent.

CHAPTER 2

REVIEW OF LITERATURE

24

2.1 Review of literature

Sina Saremi-Yarahmadi et al. [37] have reported the synthesis of

nanostructured thin films of α-Fe2O3 by atmospheric chemical vapor

deposition (APCVD) using ferrocene and iron pentacarbonyl as

precursors. They have concluded that the films prepared using

ferrocene precursor exhibited superior photoeclectrochemical

performance compared to those prepared with iron pentacarbonyl

precursor. Hence, ferrocene is a better alternative to iron pentacarbonyl

in the synthesis of hematite photoelectrodes using APCVD technique.

Jianmin Gu et al. [38] have reported a dual iron precursors

system in a hydrothermal process for the controllable fabrication of α -

Fe2O3 hierarchical structures with different morphologies such as micro-

pines, snowflakes and bundles. The two iron precursors were

successfully synthesized by tuning the total concentration of the two

iron precursors K4[Fe(CN)6] and K3[Fe(CN)6] and their molar ratio. The

α-Fe2O3 hierarchical structures exhibited good photocatalytic properties

for the degradation of salicylic acid.

The use of Advanced Fenton Process (AFP) using zero valent

metallic iron (ZVMI) for the removal of the azo dye, methyl orange (MO)

was studied by Gomati Devi et al. [39]. They have reported that the

degradation rate decreased with increase in dosage of iron and also at

higher oxidant concentrations which was attributed to the surface

precipitation leading to the deactivation of the iron surface. The results

25

indicated that the degradation of MO using Fe(0) is an acid driven

process with maximum efficiency at pH 3. The efficiency of different

processes for the decolorization of MO followed the order:

Fe(0)/H2O2/UV > Fe(0)/ H2O2/dark > Fe(0)/APS/UV > Fe(0)/UV >

Fe(0)/APS/dark > H2O2/UV≈Fe(0)/dark > APS/UV.

Gad and Sayed [40] have reported the use of activated carbon

prepared from bagasse pith for the removal of rhodamine B (RhB) by

adsorption. The effect of various parameters such as pH, particle size,

agitation time, temperature, initial dye concentration and desorption was

studied. The results indicated that the activated carbon was an effective

adsorbent for the removal of RhB. The adsorption capacity, qm was

263.85 (mg.g-1) at an initial pH of 5.7 for a particle size of 0.25 nm and

equilibrium time of 240 minutes at a temperature of 200C and initial dye

concentration range of 100-600 (mgL-1). The adsorption process obeyed

Langmuir adsorption isotherm and followed pseudo-second order

kinetics indicating that chemisorption was the major process in the

removal of RhB.

Dengsong Zhang et al. [41] have reported the synthesis of CeO2

hollow nanobeads by means of a solvothermal treatment combined with

controlled calcinations. The nanobeads were characterized by TEM,

EDS, XRD and XPS. The nanobeads with polycrystalline face-centered

cubic phase exhibited uniform morphology ranging from 150 to 200 nm

in outer diameter and 40 to 60nm in inner diameter. The CeO2 hollow

26

nanobeads were found to exhibit excellent catalytic performance for the

oxidation of carbon monoxide.

Jiao Hua and Yang Heqing [42] have reported the deposition of

urchin-like α-Fe2O3 superstructures on Si substrate using thermal

decomposition of FeCl3 solution at 200 to 600°C and their morphologies

and structures were determined by transmission electron microscopy

(TEM), scanning electron microscopy (SEM) and X-ray diffraction

(XRD). The urchin-like superstructures exhibited a polycrystal with the

rhombohedral structure. They have reported that the

photoluminescence spectrum of the urchin-like superstructures consists

of a weak emission peak at 548 nm (2.26 eV).

Wei Zheng et al. [43] prepared α -Fe2O3 ceramic nanofibers by

electrospinning of polyvinyl alcohol/Fe(NO3)3.9H2O composite

nanofibers followed by calcination. The gas sensing properties of the

nanofibers were investigated. The results indicated that the fibers

indicated rapid response-recovery and high sensitivity characteristics to

ethanol vapor with response and recovery time of about 3 and 5

seconds respectively.

Rajesh Kumar et al. [44] have reported the successful synthesis

of polyhedral nanocrystals of α-Fe2O3 by annealing ferric chloride on

silicon substrate at 1000 °C in the presence of hydrogen gas diluted

with argon. The nanoparticles exhibited uniformly shaped polyhedral at

1000°C and irregular shapes at 950 °C. It was reported that polyhedral

27

formation of α-Fe2O3 nanocrystals depends upon the annealing

temperature and the surface morphology was mainly dependent on the

gas flow rate inside the reaction chamber.

Xiaoli Xie et al. [45] have reported the construction of α-Fe2O3

nanostructures by a novel hydrothermal route using a mixture of ferric

chloride and sodium sulphate. The photocatalytic and magnetic

properties of the α-Fe2O3 superstructures were studied. The results

indicated that the hollow microspheres constructed using α-Fe2O3

nanorods acted as effective photocatalyst for the degradation of methyl

orange.

Y. R. Smith et al. [46] have reported the synthesis of sulfated

Fe2O3–TiO2 by treatment of ilmenite ore with sulfuric acid. The

compound was calcined upto 900 ◦C. The photocatalytic activity of the

compound was evaluated by the oxidation of 4-chlorophenol in aqueous

medium under UV–visible and visible light irradiation. It was found that

the compound calcined at 500 ◦C had a band gap value of 2.73 eV and

exhibited the highest photocatalytic activity. It was concluded that the

better photocatalytic activity of the compound in comparison to high

surface area sulfated titania (275 m2g-1) was due to the presence of

iron, despite the low surface area of the samples (12–17 m2g-1).

The synthesis of C, S, N and Fe-doped TiO2 photocatalysts by a

facile sol–gel method was reported by Xiangxin Yang et al. [47]. The

photocatalytic activities of the multi-doped TiO2 catalysts for the

28

degradation of rhodamine B (RhB) in aqueous solution under visible-

light irradiation were studied. The results indicated that the

photocatalytic activity significantly increased due to doping and the

catalyst doped with nitrogen, carbon, sulfur, and 0.3 wt% iron had the

highest photocatalytic activity.

J. Huang et al. [48] have reported the synthesis of hematite solid

spindles and hollow spindles via a template-free, economical

hydrothermal method, using ferric chloride and sodium hydroxide.

PXRD pattern of the product indicated the presence of α-Fe2O3. SEM

and TEM measurements indicated that the products were in the shape

of solid spindles and hollow spindles respectively. It was found that the

porous hollow hematite spindles exhibited better performance as gas

sensors in comparison to other hematite nanostructures due to their

large surface area and porous hollow structure.

T.K. Ghorai et al. [49] synthesized nano-structured Fe(III)-doped

TiO2 photocatalysts with anatase. The efficiency of the photocatalyst for

the removal of non-biodegradable organic dyes like methyl orange

(MO), rhodamine B (RhB), thymol blue (TB) and bromocresol green

(BG) under UV light irradiation was studied. The different compositions

of FexTi1-xO2 (x = 0.005, 0.01, 0.05, and 0.1) nanocatalysts synthesized

by chemical method were characterized by PXRD, UV–vis diffuse

reflectance spectra, specific surface area (BET), transmission electronic

microscopy (TEM) analysis, XPS, ESR and zeta potential. The PXRD

29

results indicated that all the compositions of Fe(III) doped TiO2

photocatalysts exhibited only anatase phase not rutile phase. For

complete degradation of all the solutions of the dyes (MO, RB, TB, and

BG), the composition with x = 0.005 was found to be more efficient

compared to all other compositions of FexTi1_xO2 and degussa P25.

The decolorization rate of different dyes decreased as the Fe(III)

concentration in TiO2 increased.The energy band gap of Fe(III)-doped

TiO2 was found to be 2.38 eV.

Slavica Zecet et al. [50] have reported the reduction of

commercial and mechanochemically processed CeO2 nanopowder.

Nanocrystalline CeO2 with a crystallite size of about 21 nm was

obtained during 60 min of milling in a high-energetic vibratory mill. The

nanopowder was characterized by PXRD, SEM and BET method. It was

found that during the thermal treatment at 1200 and 14000C in an argon

atmosphere, the nonstoichiometric CeO2-x oxides with the defect fluorite

structure were formed. Compositions of CeO2-x oxides were determined

according to its lattice parameter. The results indicated that the release

of oxygen and the rate of reduction were more effective in

nanocrystalline CeO2 than in the microcrystalline CeO2.

Mn-doped CeO2 samples with atomic ratios equal to 0.5%, 1%

and 3% were prepared by T. Zhang et al. [51] by the conventional

mixed-oxide method using commercial cerium oxide and manganese

dioxide powders. The effect of Manganese doping on the densification

30

behavior of CeO2 was investigated by means of dilatometer and

scanning electron microscopy. It was found that the Mn doping resulted

in a decrease in the sintering temperature and an increase in the grain

growth. It was also observed that under the isothermal sintering

condition, the grain growth activation energy (Q) decreased from

731±61 kJ/mol for pure CeO2 to 593±53 kJ/mol for 1% Mn-doped CeO2.

H. Li et al. [52] have reported the preparation of flower-like

mesoporous Mn-doped CeO2 microspheres with three-dimensional (3D)

hierarchical structures by a hydrothermal method using glucose and

acrylic acid. The products were characterized by H2-TPR, XPS, SEM,

XRD, N2 adsorption/desorption, Raman spectra and so on. It was found

that the atomic ratios of Mn/(Ce + Mn) in the Ce–Mn–O samples as well

as their morphologies affected their catalytic performances for the low

temperature catalytic combustion of trichloroethylene. The flower like

Ce–Mn–O microspheres possessed excellent activity and high stability,

in comparison to pure flower-like CeO2 microspheres or bulk Ce–Mn–O

samples. The activity was highest for flower-like sample with Mn/(Ce +

Mn) atomic ratio of 0.21. It was concluded that the high catalytic

performance of flower-like Mn-doped CeO2 microspheres compared to

that of general Ce–Mn–O mixed oxides was due to their high surface

area, high oxygen mobility and rich surface active oxygen species.

B.Z. Matović et al. [53] synthesized nanocrystalline Ce1-xCuxO2

samples (0 ≤ x ≤ 0.15) by self-propagating room temperature synthesis.

31

The vibration properties of the materials and the solubility of Cu in the

ceria lattice were determined by Raman spectroscopy and PXRD. The

results indicated that the obtained powders having low dopant

concentration were solid solutions with a fluorite structure. However,

when the Cu content was higher than 7.5% by mass, phase separation

was observed and the two oxide phases, CeO2 and CuO were found to

coexist. All the powders were nanometric in size and possessed high

specific surface area.

X. Wu et al. [54] synthesized a series of MnOx-CeO2 mixed oxides

by a sol-gel method followed by calcination at different temperatures.

The soot oxidation activities of the mixed oxides were determined for

different NO concentrations under loose contact conditions. A quasi-

parabolic curve was observed for the apparent dependency of activity

on the surface of the catalyst. It was observed that, for a surface area

below 8 m2g-1, the soot oxidation was limited by the availability of NO2

because of the separation and sintering of the mixed oxides.

Dziembaj et al. [55] prepared a series of nanocrystalline Ce–Cu

oxide by a modified reverse microemulsion method using a mixture of

cerium and copper nitrate solutions with various precipitating agents

such as ammonium carbonate, sodium hydroxide etc. The catalytic

efficiency of the oxide for the incineration of methanol and ethylene was

studied. It was found that the efficiency was mainly dependent on the

copper loading and the size of the nanocrystalline material. From a

32

careful observation of the results, the optimal composition and

morphology of the catalyst were proposed.

K. Chayakul et al. [56] have studied the catalytic activities of Re–

Co/CeO2 bimetallic catalysts for the water gas shift (WGS) reaction. The

activities of the catalyst were compared with those of Co/CeO2. The rate

of WGS reaction over Re–Co/CeO2 bimetallic catalysts was found to be

higher than that of Co/CeO2. The presence of Re influences the catalyst

performance in many ways. XRD and Raman studies indicated that

metal oxides were dispersed on CeO2 surface and H2-chemisorption

indicated better dispersion of Co on the surface of CeO2 upon addition

of Re. The X-ray absorption near edge structure (XANES) spectra of

Re–Co/CeO2 catalysts indicated that the presence of Re promotes the

reduction of surface ceria to Ce2O3 and provides oxygen vacancies

which facilitate the redox process at the surface. All these effects were

found to increase the rate of WGS reaction.

Y. Tian et al. [57] synthesized Fe3O4 nanoparticles in the solution

involving water and ethanol. The α-Fe2O3/Fe3O4 core-shell

nanostructures were produced by the production of α-Fe2O3 in situ on

the surface of the Fe3O4 nanoparticles by surface oxidation in molten

salts. The oxidation of the primary Fe3O4 nanoparticles resulted in a

change in magnetic properties from ferromagnetism to

superparamagnetism. It was also observed that the α-Fe2O3/Fe3O4

core-shell nanoparticles acted as an efficient photocatalyst for the

33

removal of methyl orange than the α-Fe2O3 nanoparticles. The

photocatalyst was recyclable by applying an appropriate magnetic field.

Y. Wang et al. [58] conducted various experiments to study the

influence of kinetics and intermediate compound of pyrene

photodegradation by iron oxides. The experiments were considered as

an attempt to get a better understanding of the photodegradation of

polycyclic aromatic hydrocarbons (PAH) in solid phase in natural

environment. An examination of the results indicated that the pyrene

photodegradation rate followed the order:

α-FeOOH > α-Fe2O3 > γ-Fe2O3 > γ–FeOOH

under same reaction conditions. The rate of photodegradation of pyrene

was found to increase with a lower dosage of α-FeOOH and higher light

intensity. Iron oxides and oxalic acid can be considered to set up a

photo-Fenton-like system without additional H2O2 in solid phase to

increase the photodegradation of pyrene under UV light irradiation. The

photodegradation reaction was found to follow the first-order reaction

kinetics. The half-life (t1/2) of pyrene in the system exhibited higher

efficiencies of using iron oxide as photocatalyst to degrade pyrene. The

intermediate compound pyreno was detected during photodegradation

reaction with the help of gas chromatography–mass spectrometry (GC–

MS). The photodegradation efficiency for PAHs in the photo-Fenton-like

system was also confirmed by conducting the experiments with

contaminated soil samples. It was concluded that the work provided

34

some useful information to understand the remediation of soils

contaminated by PAHs by photochemical techniques under practical

condition.

Gajendra Kumar and K. M. Parida [59] reported the fabrication of

nanostructured and mesoporous Fe-Ce mixed oxides. Phase, electronic

structure and other properties of the products were determined by both

low-angle and wide-angle XRD, DRS, TEM, Raman spectroscopy, XPS

and N2 adsorption-desorption isotherm methods. Analytical results

demonstrated that the photocatalyst was in the nanometer range and

mesoporous in nature. The photocatalytic removal of phenol, methylene

blue (MB) and congo red (CR) was studied. It was observed that 13 %

and 93 % removal occurred in case of phenol and methylene blue

respectively. There was almost complete removal of congo red. The

higher photocatalytic activity of 1:1 (Fe/Ce) sample was ascribed to its

higher surface area and surface acidity which determine the active sites

of the photocatalyst and accelerate the rate of photocatalytic reaction.

S.K. Kansal et al. [60] studied the photocatalytic degradation of

methyl orange and rhodamine B by using various photocatalysts such

as TiO2, ZnO, SnO2, ZnS and CdS. Effect of various factors such as

catalyst dosage, initial dye concentration and pH was also studied.

Maximum decolorization (more than 90%) of the dyes was achieved

with ZnO and at basic pH. The percentage dye removal was highest

under UV/solar system and the COD reduction occurred at a faster rate

35

in solar light than in UV light. The performance of ZnO/solar light system

was better than ZnO/UV system.

Ani Idris et al. [61] have reported the synthesis of magnetically

separable photocatalyst beads containing nano-sized Fe2O3 in alginate

polymer. The magnetic photocatalyst beads were used in a slurry-type

reactor. The magnetism of the catalyst was due to nanoparticles of γ-

Fe2O3, by which the catalyst can be easily recovered by the application

of an external magnetic field. It was found that the beads were sunlight-

driven photocatalyst. No chromium reduction was observed in system

without the magnetic photocatalyst beads under sunlight irradiation due

to the stability of the chromium (VI). When the magnetic photocatalyst

beads were added, the photo-reduction of Cr (VI) was achieved in just

50 minute under sunlight irradiation which was attributed to the

photocatalytic activity of the beads. However, in the absence of sunlight,

the reduction of chromium was just about 10%. The observations were

explained in terms of the absorption occurrence of chromium (VI) on the

surface of the catalyst. At lower pH, the rate of photoreduction of

chromium (VI) was more significant. It was concluded that the use of

magnetically separable photocatalyst beads is a feasible strategy for the

elimination of Cr (VI).

B. David et al. [62] have reported the synthesis of γ-Fe2O3

nanoparticles by adding a gaseous mixture of H2/Fe(CO)5 into a

microwave torch discharge at a pressure of 1 bar. The PXRD pattern

36

indicated the presence of the γ-Fe2O3 phase with a mean crystallite size

of about 24 nm. The Mossbauer spectrum recorded at 5K indicated the

dominating characteristic sextets of γ -Fe2O3. The presence of pure

Fe3O4 in the nanopowder was excluded. The Mössbauer spectrum also

exhibited six times larger total spectrum area than the Mössbauer

spectrum taken at 293K. The zero field cooled/field cooled curves

measured down to 4K in the magnetic field of 7.9 kA/m were reported.

The synthesis MCM-41/CeO2 and MCM-48/CeO2 by direct and

indirect methods in solvent media and by grinding method in a solvent-

free media has been reported by H. R. Pouretedal and Mina Ahmadi

[63]. The materials prepared by grinding method were characterized by

XRD, FTIR and N2 adsorption-desorption method. Surface areas and

pore size of MCM-48/CeO2 were found to be 680.9 m2g−1 and 1.64 nm

respectively. It was observed that the CeO2 nanoparticles were

introduced into MCM-41 and MCM-48. The MCM-41/CeO2 and MCM-

48/CeO2 materials were used for the photocatalytic degradation of

congo red dye as a pollutant. The MCM-41/CeO2 and MCM-48/CeO2

prepared by grinding method exhibited higher photocatalytic activity

with 97.6 % and 93.1 %, respectively for the degradation of congo red.

The higher photocatalytic activity was attributed to the complete

incorporation of Ce4+ in mesoporous material of MCMs in a solvent-free

media.

37

W. Wang and S. Yang [64] have reported the synthesis of

silicotungstic acid and phosphotungstic acid. The characterization of the

products was done by FTIR and XRD. The results indicated that the

prepared catalysts possessed the classical Keggin structure. The

products were used for the photodegradation of methyl orange. The

factors such as the kind of catalyst, the dosage of catalyst, the initial

dye concentration and irradiation time were investigated. The results

indicated that the degradation of methyl orange was about 93.6% with

phosphotungstic acid with 8.89 gL-1 concentration of phosphotungstic

acid, 5.56 mgL-1 concentration of methyl orange and an irradiation time

of 80 minutes.

W.K. Chang et al. [65] prepared a visible light photocatalyst

CaIn2O4 by the solid-state reaction between ball milled powders of

CaCO3 and In2O3. During the process of preparation, a novel core shell

like composite In2O3@CaIn2O4 was observed at intermediate calcination

temperatures. The coupled phases obtained in the temperature range of

873–1323 K were characterized by PXRD, TEM and UV–visible diffused

reflectance spectroscopy. The coupled composite phases

In2O3@CaIn2O4 exhibited superior photocatalytic activity for removal of

methylene blue under visible light irradiation compared to single phase

CaIn2O4. The probable reasons for the enhanced photocatalytic activity

of the composite catalyst were selective charge separation and efficient

charge transport at the interface upon illumination with visible light.

38

Hajira Tahir and FahimUddin [66] studied the adsorption of the

dye acid red 4 on pure alumina and alumina supported metals. The

effect of temperature, amount of adsorbent and shaking time was also

studied. The impregnation technique was used for doping Al2O3 with

divalent metals such as nickel and zinc resulting in the formation of Ni

0.001–Al2O3, Ni 0.01–Al2O3, Zn 0.001–Al2O3, Zn 0.01–Al2O3 adsorption

systems. The data were analyzed using Langmuir, Freundlich and

Dubinin–Radushkevich adsorption isotherms. The Langmuir’s constant

K was used for calculating the thermodynamic parameters such as

enthalpy change (∆H), free energy change (∆G) and entropy change

(∆S) of adsorption. The sorption mean free energy (E) for each system

was determined from the Dubinin–Radushkevich equation.

R. M. Mohamed and E. S. Aazam [67] have reported the

synthesis of CeO2-SiO2 nanoparticles by a facile microwave-assisted

irradiation process. The effect of microwave irradiation time was

studied. The characterization of the materials was done by N2

adsorption, XRD, UV-visible/DR and TEM. All the solids exhibited

mesoporous textures with high surface areas, relatively small pore size

diameters and large pore volumes. The XRD results indicated that the

nanoparticles exhibited cubic CeO2 without impurities and amorphous

silica. The TEM images revealed that the particle size of CeO2-SiO2

nanoparticles, which were prepared by microwave method for 30 min

irradiation times was around 8 nm. The photocatalytic activities of the

39

nanoparticles were determined by the decomposition of methylene blue

under UV light irradiation. The results indicated that the microwave

produced CeO2-SiO2 nanoparticles had the best crystallinity under a

shorter irradiation time. This is an indication of the fact that the

introduction of the microwave can really save energy and time with

faster kinetics of crystallization. The highest photocatalytic activity was

exhibited by the sample prepared by 30 min microwave irradiation time.

G.R. Bamwenda and H. Arakawa [68] have reported the use of

CeO2 as a potential photocatalyst for the decomposition of water to

produce oxygen in aqueous suspension containing an electron

acceptor. They have investigated the optimum parameters for the

reaction. The O2 yield was strongly dependent on the irradiation time,

CeO2 concentration, concentration of the electron acceptor and the pH

of the suspension. The optimum photo production of O2 was obtained at

pH 3 for a CeO2 concentration of 2-5 gdm-3 when the irradiation time

was 10 hours. The results indicated that the system utilizes CeO2 to

accomplish the initial light absorption, charge separation, and O2

evolution from the interaction of water molecules with the holes

generated in the valence band of CeO2 upon irradiation in the presence

of an electron acceptor. It was concluded that with an appropriate

design, CeO2 can be considered as a promising material to be used as

a photoactive component in photocatalytic reactions.

40

J.F. Lima et al. [69] synthesized ultrafine systems of ZnO and

CeO2 for use as ultraviolet filters by a nonalkoxide sol–gel process at

different temperatures to obtain solid materials (40 and 70°C). The

systems were characterized by X-ray diffraction, scanning electron

microscopy and UV–vis reflectance. The catalytic and photocatalytic

activities of the systems were also studied. The ZnO:CeO2 systems

were found to exhibit higher UV absorption and transparency in the

visible region. The photocatalytic activity of the ZnO:CeO2 systems for

the oxidation of organic materials was much lower than that of TiO2,

CeO2 and ZnO indicating that ZnO:CeO2 systems are promising

candidates for use as optical materials in UV-filters.

A. Qurashi et al. [70] employed a simple and novel chemical

approach to prepare α-Fe2O3 nanoparticles. FESEM analysis revealed

that the nanoparticles exhibited monodispersed nanoellipsoid

morphology. The short and the long axes of the ellipsoids were found to

be in the range of 50-60 nm and 40-50 nm respectively. XRD analysis

supported that the nanoparticles exhibited α-Fe2O3 phase. TEM and

HRTEM analysis showed that the α-Fe2O3 nanoellipsoids consisted of

single crystals. The photocatalytic removal of methylene blue was

studied for different irradiation time. It was observed that there was total

decomposition of the dye when the irradiation time was 220 minutes.

Nanocrystalline CuO was synthesized by using waste printed

circuit boards by Shiue et al. [71]. The nano metal oxide was used as

41

adsorbent for the removal of methyl orange from its aqueous solution by

the batch adsorption technique at temperature of 30 to 60 °C. The

adsorption capacity was found to increase with increase in the

concentration and temperature but decreased with the adsorbent

dosage. The adsorption data was analyzed using Langmuir and

Freundlich adsorption isotherms. The experimental data fitted well with

the Langmuir isotherm. In order to understand the adsorption

mechanism, three kinetic models, viz., the pseudo-first order, the

pseudo-second and the intraparticle diffusion models were used. It was

noticed that the adsorption process followed the pseudo second

kinetics. It was concluded that the adsorption process appeared to be

controlled by more than one step, namely both the external mass

transfer and intraparticle diffusion mechanisms. MO was more efficiently

adsorbed on the surface of CuO. Hence CuO could be used as an

alternative adsorbent material for the removal of anionic dyes in

wastewater treatment.

S. Al-Qaradawi and S.R. Salman [72] used TiO2 as a

photocatalyst for the removal of methyl orange under solar light

irradiation. It was found that there was no degradation of the dye in the

dark in the presence of TiO2. It was also observed that no degradation

was observed when the dye solution was placed in sunlight but without

TiO2. A number of experiments were conducted to optimize the

experimental parameters. In the first set of experiments variable

42

amounts of TiO2 were used with a fixed concentration of MO. Maximum

removal of MO was attained at pH 3 for a catalyst dosage of o.4% when

the dye concentration was 4 × 10−5 M.

The photocatalytic activity of mesostructured TiO2 nanoparticles

to remove methyl orange dye from its aqueous solution under UV light

irradiation was studied by Ke Dai et al. [73]. It was found that 98%

removal of MO can be achieved for a catalyst dosage of 1.0 gL-1 for an

irradiation time of 45 minutes at pH 2. The mechanism of photocatalytic

degradation of methyl orange involved three intermediate processes:

demethylation, methylation and hydroxylation. Among these processes,

demethylation was more favorable than hydroxylation, but hydroxylation

resulted in the largest number of intermediates. The degradation

pathway of MO under the optimum conditions was also proposed.

J.M. Soltaninezhad and A. Aminifar [74] made a comparison of

the photocatalytic activity of nano particles of ZnO was prepared by

different methods by selecting methylene blue as the model compound

under ultraviolet light. They have reported that such semiconductors

can degrade most kinds of persistent organic pollutants, such as

detergents, dyes, pesticides and volatile organic compounds under UV-

irradiation. In some cases, the photocatalytic activity of the coupled

photocatalysts, evaluated using the photodegradation of organic dyes

as a probe reaction showed an increase in photocatalytic activity in

different coupled photocatalysts. It was found that the ZnO

43

nanostructures and nanocrystalline ZnO exhibited different activities for

the degradation of methylene blue. The characterization of the

photocatalyst was done by BET, XRD, TEM, AFM, Raman and FTIR

spectroscopy.

Jianjun Liao et al. [75] successfully prepared a new type of

TiO2/Ti mesh photoelectrode by anodization in ethylene glycol solution.

.The three-dimensional arrays of nanotubes formed on the Ti mesh

exhibited a significant improvement in photocatalytic activity compared

to the nanotube arrays formed on the foil. This was evident by about 22

and 38% enhancement in the efficiency per mass and per area

respectively; when the TiO2/Ti mesh electrode was used for the

photodegradation of methyl orange. The effect of various parameters on

the rate of photodegradation such as different photoelectrode

calcination temperatures, pH and the presence H2O2 was also studied.

It was observed that the photocatalytic activity was highest for the

TiO2/Ti mesh photoelectrode calcined at 550°C, due to the appearance

of mixed phases of anatase and rutile. In strong acidic or alkaline

conditions, such as pH 1 or 13, high degradation efficiency was

achieved. The presence of H2O2 promotes photocatalytic efficiencies.

The experimental results also demonstrated the excellent stability and

reliability of the TiO2/Ti mesh electrode.

F. Meng et al. [76] deposited thin films of nano TiO2 by radio

frequency magnetron sputtering using TiO2 ceramic target. The films

44

were characterized by XRD, AFM and UV-visible spectroscopy. The

films were found to be amorphous with an energy gap of 3.02 eV. The

photocatalytic activity of the films was evaluated by studying the

degradation of methyl orange under UV light irradiation. The films

exhibited efficient photocatalytic activity towards the removal of MO.

The photocatalytic degradation followed first order kinetics.

M. Vinoth et al. [77] investigated the removal of methyl orange

from various aqueous solutions by adsorption on ground yam leaf fibers

with size ranging from 212-350 microns. The effect of various factors

such as pH, dosage of the adsorbent, contact time and initial dye

concentration was also studied. Three adsorption isotherms namely;

Langmuir, Freundlich and Temkin-Pyzhev isotherm models were used

to analyze the adsorption data. The data fitted well for the Freundlich

isotherm model with an adsorption capacity and adsorption intensity of

2.40 and 1.14, respectively.

S. Koner et al. [78] collected silica gel waste (SGW) from solid

waste of a local factory at Kolkata, India. The silica gel waste was

modified with cationic surfactant and then used as an adsorbent for the

removal of methyl orange dye from aqueous solution. In case of batch

adsorption studies, the kinetic study, isotherm study and effect of

temperature and shaking speed were studied. The sorption followed the

pseudo second order reaction kinetics and obeyed Langmuir adsorption

isotherm. Chemisorption was the rate limiting step for adsorption.

45

The preparation of activated carbon from coconut shell fibers has

been reported by K. P. Singh et al. [79]. The activated carbon was used

as adsorbent for the removal of methylene blue and methyl orange dyes

from wastewater. The adsorption studies were carried out at different

temperatures, particle size, pH and adsorbent doses. The adsorption

data was correlated with both Langmuir and Freundlich isotherm

models. It was found that the adsorption data fitted well for the

Freundlich isotherm model compared to the Langmuir isotherm. The

adsorption of both methylene blue and methyl orange dyes followed

first-order kinetics. A study of various kinetic parameters such as the

mass-transfer coefficient, effective diffusion coefficient, activation

energy and entropy of activation was conducted to establish the

mechanisms. It was concluded that the adsorption of methylene blue

occurred through a film diffusion mechanism both at low as well as high

concentrations. On the other hand, the adsorption of methyl orange

occurred through film diffusion at low concentration and particle

diffusion at high concentrations. It was also concluded that the sorption

capacity of the prepared activated carbon was comparable to other

available adsorbents and was also economical.

N. Barka et al. [80] studied the photocatalytic degradation of

methyl orange by nanocrystalline TiO2 under UV light irradiation. The

experimental results revealed that the photocatalytic degradation rate

was greatly affected by the dye concentration and the solution

46

temperature. The photocatalyic degradation was favored by higher dye

concentration as well as high temperature. A simple kinetic model was

proposed to describe the concentration of MO during the photocatalytic

process in an adequate way. There was close agreement between the

calculated results and the experimental data.

X. T. Zhou et al. [81] studied the photocatalytic activity of meso-

tetraphenylporphyrins with different metal centers (Fe, Co, Mn and Cu)

adsorbed onto the surface of TiO2 (Degussa P25) using the azo dye

methyl orange as model compound under visible and UV light

irradiation. The characterization of the photocatalyst was done by XRD,

SEM, DRS-UV-visible and FTIR spectroscopy. In case of both UV and

visible light irradiation, the photocatalyst exhibited a greater efficiency

for the removal of MO. The analysis of natural bond orbital (NBO)

charges indicated that methyl orange ion was adsorbed easily by CuP-

TiO2 photocatalyst due to an increase in the induced interactions.

X. Liu and C. Dong [82] studied the combined COD and nitrogen

removal from domestic wastewater using a micro-aerobic granular

sludge reactor. The effect of oxygen flux, hydraulic retention time,

biomass concentration and sludge loading was also studied. The

reactor exhibited stable and effective COD removal through the

experiment. However, the nitrogen removal was mainly dependent on

the mode of operation. Under the optimum conditions, the total nitrogen

47

(TN) removal efficiency achieved was 82%, and the concentrations of

NH4+ -N and TN in the effluent were 5.5 mg/L and 8.2 mg/L respectively.

Rani Devi and R.P. Dahiya [83] studied the reduction in COD and

BOD of domestic wastewater by discarded material based mixed

adsorbents (mixed adsorbent carbon, MAC and commercial activated

carbon, CAC) in batch mode. It was found that under optimum

conditions, the maximum reduction in COD and BOD achieved using

MAC and CAC was 95.87% and 97.45% respectively for MAC; 99.05%

and 99.54% respectively for CAC. It was concluded that MAC offered

potential benefits for the reduction in COD and BOD from wastewater.

B. Balamurugan et al. [84] studied the reduction in chemical

oxygen demand (COD) and color of the effluent containing reactive

textile dye by microbial method. It was reported that the anaerobic

digestion had the potential to break down complex refractory organic

compounds so that they can be further aerobically degraded or undergo

complete mineralization. Cotton textile effluent containing the synthetic

reactive red 2 dye was subjected to anaerobic digestion technique

aiming the dye degradation. Halomonasvariabilis and Halomonasglaciei

bacteria were used for degradation in the batch-mode static condition.

The incubation temperature was kept constant at 30°C using CO2

incubator. The degradation was found to be maximum within 144 hours

of experimental run. The degradation studies were made by determining

the values of COD and BOD. Statistical analysis indicated that the COD

48

and BOD reduction rates were optimum for a concentration of 1297 mg

L-1when the time duration was about 100 hours.

S. Eker and F. Kargi [85] treated synthetic wastewater

contaminated with 4-chlorophenol (4-CP) using a rotating perforated

tubes biofilm reactor (RTBR). The effects of the feed COD, 4-CP

contents and the A/Q (biofilm surface/flow rate) ratio on percent COD,

4-CP and toxicity removal were determined with the help of Box–Wilson

statistical experiment design and response surface methodology (RSM).

It was found that the increases in A/Q ratio and the feed COD contents

enhanced the COD reduction and the 4-CP removal. It was also noticed

that the high feed 4-CP contents had an adverse effect on the

performance of the system due to toxic effects of 4-CP on the microbes.

The results indicated that more than 95% removal of 4-CP and toxicity

were achieved with an A/Q ratio of 186 m2dm-3 and feed COD of 6000

mgL-1 when the feed 4-CP content was 1000 mgL-1. It was concluded

that the RTBR was more efficient than the RBBR used for the same

purpose used in their previous studies.

F. Gómez-Rivera et al. [86] studied the fate of nanocrystalline

CeO2 during municipal wastewater treatment using a laboratory scale

activated sludge (A/S) system which was fed with primarily-treated

municipal wastewater and nanocrystalline CeO2. It was reported that

nanocrystalline CeO2 was very efficiently removed during A/S treatment

(96.6% total Ce). Extensive removal of CeO2 < 200 nm was also

49

achieved and the concentration escaping the treatment was only 0.11

mg Ce/L. The elimination of CeO2 particles occurred mainly by

aggregation and settling promoted by circum neutral pH values and also

by interactions of the nanoparticles with the organic and/or inorganic

wastewater constituents. Biosorption was also believed to contribute to

CeO2 removal. The experimental results indicated that A/S treatment

was expected to provide extensive removal of nano-CeO2 in municipal

wastewaters.

J.Q. Jiang et al. [87] have reported the comparative performance

of potassium ferrate (VI), ferric sulphate and aluminium sulphate for the

removal of turbidity, color, chemical oxygen demand (COD) and

bacteria in sewage treatment. It was found that; in case of coagulation

and disinfection of sewage, potassium ferrate (VI) was more efficient in

the removal of organic contaminants, COD and bacteria compared to

the other two coagulants. It was also found that potassium ferrate (VI)

produced less sludge volume and removed more contaminants, thus

making the subsequent sludge treatment easier.

Y. Hua et al. [88] have reported the photodegradation of

rhodamine B (RhB) under visible light irradiation by the Keggin- type

Fe(III) substituted phosphotungstic heteropolyanion

[PW11O39Fe(III)(H2O)4−(PW11Fe)] as a photocatalyst in a neutral

aqueous solution. They have proposed a visible photocatalysis

mechanism which is different from that of the dye photosensitization.

50

The effect of various factors such as the initial dye concentration, the

PW11Fe concentration and pH on the rate of photodegradation as well

as the stability of the catalyst was also studied. The interaction between

RhB and PW11Fe was discussed in detail in accordance with the visible

light absorption and fluorescence emission spectra. The results

indicated that 100% of RhB degradation was reached at 80 min under

visible light irradiation in the presence of 25 µmolL−1 of PW11Fe for the

10 µmolL−1 dye solution. About 35% removal of total organic carbon

(TOC) was achieved in 120 minutes. The photodegradation was found

to follow pseudo-first-order kinetics.

CHAPTER 3

SYNTHESIS OF THE NANO METAL

OXIDES

51

3.1 Synthesis of the nano metal oxides

Synthesis of nano metal oxides is one of the major challenges

facing the nanotechnology industry. One of the major draw backs in the

synthesis of nano metal oxides is the poor control of stoichiometry at

the nano level. Though solid state reaction is a simple process, it suffers

from major draw backs such as the weak reactivity of the starting

materials, poor homogeneity of the product and long durations.

Low temperature chemical methods have been developed to

overcome these limitations of the solid state methods. Some of these

methods are co-precipitation, sol-gel, evaporation, decomposition,

hydrothermal, aerosol hydrolysis etc. However, most of these methods

require long processing times and elaborate experimental set up. A

novel method free from these draw backs has been developed by Patil

et al. [89]. This self-propagating solution combustion method is

becoming very popular for the synthesis of nano metal oxides. Some of

the other wet chemical methods are discussed first before a detailed

study of the solution combustion method is presented.

3.1.1 Hydrothermal method

In hydrothermal method, the solution or suspension of metal salts,

oxides or hydroxides in water or organic solvent is heated in an

autoclave at a controlled temperature or pressure. The temperature is

maintained between the boiling point of water and its critical

52

temperature (Tc = 3740C) while the pressure is more than 100 kPa. The

resulting product is purified by washing with distilled water or acetone

and finally dried in air [90-92].

The different types of hydrothermal reaction types include

decomposition, oxidation, crystallization, precipitation, sintering and

leaching. However, the nano metal oxides are usually prepared either

by hydrothermal precipitation or by hydrothermal crystallization. In

hydrothermal precipitation, a clear solution of the metallic salt is used

whereas in hydrothermal crystallization, hydroxyl gels or sols are used.

By hydrothermal method the formation of hard aggregates can be

avoided [93-95].

3.1.2 Sol-gel method

In this method, an aqueous solution formed from the nitrate salts

of inorganic cations is heated at a moderate temperature (150 to 2500C)

to produce a solid polymeric resin. The precursor can either be an

inorganic salt or organic compound known as alkoxide. In case of

alkoxide precursors, the byproducts like alcohol and water can be easily

removed during the drying process [96-98]. The nano metal oxides

obtained by sol-gel method have better purity. The method can be used

for the preparation of special products such as films and fibers [99-101].

3.1.3 Co-precipitation method

The co-precipitation method can be used for the preparation of

more homogeneous powders. The main drawback of this method is that

53

the required stoichiometry is lost during filtration owing to large

differences of solubility among the precipitates. As the number of

components increases, it becomes difficult to find a suitable

precipitating agent. This can be greatly overcome by using aqueous

organic – gel method where inorganic powders are produced by using

polyfunctional hydroxyl acids and metal salts to form soluble complexes

in aqueous solution. The clear solution is dehydrated and the

amorphous precursor so formed is heated at elevated temperatures to

get the desired nano crystalline compound [102-104]. By co-

precipitation technique, one can achieve homogeneous mixing at the

atomic scale and have a good control over stoichiometry. The technique

is suitable for the synthesis of active nano metal oxides from

commercially available chemicals in short intervals of time [105, 106].

3.2 Solution combustion synthesis

Some of the drawbacks of wet chemical methods are long

processing time, expensive chemicals, special experimental set up and

long sintering or annealing processes. Combustion synthesis can be

employed for the synthesis of homogeneous, very fine and crystalline

nano metal oxides in few minutes. This method requires a low

temperature of about 3000C as against 13000C needed for the solid

state method [107-112].

54

Combustion synthesis is also referred as fire synthesis as well as

self-propagating high temperature synthesis (SHS). Fire can be

regarded as an uncontrolled combustion which produces heat, light and

ash. A highly exothermic redox reaction occurs between the fuel and

the oxidizer. The generation of fire requires fuel, oxidizer and right

temperature. These three elements make up a fire triangle as shown in

Figure 3.1.

Figure 3.1 The Fire Triangle

In case of a redox reaction, both oxidation and reduction occur

simultaneously. For a redox reaction to be self-propagating, the heat

liberated during combustion should be more than the heat required for

initiating the combustion process. The term combustion encompasses

flaming (gas-phase), smoldering (solid-gas) as well as explosive

reactions. It can be linear or volume combustion. In case of linear

combustion, the burning surface recedes from top to bottom in layers,

55

whereas volume combustion involves the ignition of the entire reaction

mixture to burn with a flame.

In this method the nano metal oxides are prepared by chemical

combustion reaction that propagates over starting reactive mixture due

to layer by layer heat transfer. The technique requires a high

temperature (more than 10000C) for ignition and can propagate only

through a narrow zone. Minimal amounts of gases are produced

compared to the case of explosives and propellants. The metal

reactants and fuel are made into a rod and then ignited. The chemical

reaction is initiated by an electric spark to propagate the reaction. The

combustion approach can be modified and used for the synthesis of

nano metal oxides. In this case, the thermal decomposition of metal

hydrazine carboxylate precursors such as

(N2H5)M1/3Fe2/3(N2H3COO)3.H2O (where M = Mg, Fe, Mn, Co, Ni, Zn)

takes place. The decomposition is observed to undergo smoldering

(heterogeneous) type of combustion. These precursors can ignite at low

temperatures and decompose autocatalytically using atmospheric

oxygen to yield fine particles of simple and mixed metal oxides. During

the decomposition, large amounts of gases are evolved which dissipate

heat thereby preventing the oxides from sintering. Oxides such as α-

Fe2O3, γ- Fe2O3, CeO2, MFe2O4 (where M = Ni, Mg, Mn, Fe, Co and

Zn), M1-xM1

xFe2O4 (where M = Ni, Mg: M1 = Zn, Mn) and MCo2O4

(where M = Mg, Mn and Zn) have been prepared using the

56

corresponding hydrazine carboxylate precursors. The advantage of

these precursors is that they are isomorphous, which facilitates the

preparation of a wide range of solid solutions. The precursors for other

oxides like chromites and rare earth transition metal oxides, LnBO3

(where B = Al, Cr, Mn, Fe, Co and Ni) cannot be prepared by this

method.

The SHS process is useful for the preparation of a large number

of technologically useful oxide materials such as refractories, magnetic,

semiconductors, dielectrics, catalysts, sensors, phosphors, etc. It is also

useful in the preparation of non-oxide materials such as carbides,

nitrides, borides, silicides etc. The synthesis of these materials involves

solid-state reaction between the corresponding metals and nonmetals.

This process involves high purity precursors, which ignite at

temperatures greater than 10000C. The process is highly exothermic

(Tad ~ 40000C) and is self propagating resulting in the formation of

coarse products. However, being a solid-state reaction, it does not

usually produce homogeneous products and results in coarse powders.

In comparison to SHS, The self propagating low temperature

solution combustion synthesis (SCS) has a number of advantages. The

combustion temperature of SHS is normally above 20000C. The size of

the metal oxide nanopowder produced by SHS is comparatively larger.

In case of SCS, the flame temperature is about 1000 to 16000C and the

reaction gets completed in several minutes.

57

SCS is a versatile method for the synthesis of single phase

composites, solid solutions as well as complex compound oxide phases

in homogeneous form. The method has the advantage of crystallites

without any growth and also has the potential to scale up. Because of

the gas evolution, large particles or agglomerates can be disintegrated

during the process and the products formed are of high purity. The

resulting product is in the form of very fine particulates of friable

agglomerates that can be easily ground to obtain a much finer particle

size [113-115].

3.2.1 Calculation of stoichiometry

In order to understand the highly exothermic nature of the redox

reaction in case of SCS, the concepts used in propellant chemistry have

to be employed. A solid propellant comprises of an oxidizer like

ammonium perchlorate and a fuel like carboxy terminated

polybutadiene together with aluminium powder and some additives. The

specific impulse (Isp) of a propellant is a measure of the energy released

during the combustion. It is given by the ratio of thrust produced per

pound of the propellant and is calculated using Equation 3.1.

..... (3.1)

where k is the Boltzmann constant and Tc is the temperature of the

chamber in the rocket motor. The highest value of Tc can be achieved

when the equivalence ratio (Φc) is unity.

58

The equivalence ratio of an oxidizer and fuel mixture is expressed

in terms of the elemental stoichiometric coefficient. Φc can be calculated

using Equation 3.2.

.....

(3.2)

A mixture is said to be stoichiometric when Φc= 1, fuel lean when

Φc> 1 and fuel rich when Φc< 1. Stoichiometric mixtures usually produce

maximum energy.

The oxidizer/fuel molar ratio (O/F) required for the stoichiometric

mixture (Φc= 1) is determined by summing the total oxidizing and

reducing valencies in the oxidizer compounds and dividing it by the total

oxidizing and reducing valencies in the reducing compounds. In this

case, the only oxidizing element is oxygen. Carbon, hydrogen and metal

cations are reducing elements whereas nitrogen is neutral. The

valencies of oxidizing elements are negative and those of reducing

elements are positive. For nitrogen, the valency is considered as zero.

In case of calculations involving solution combustion synthesis,

the valencies of the oxidizing elements are modified and considered as

negative and those of reducing elements as positive. Accordingly, the

elemental valencies of C, Zn and H are +4, +2 and +1 respectively and

oxidizing valency of oxygen is taken as −2. The valency of nitrogen is

considered as zero since it gets converted to dinitrogen (N2).

59

For example, the oxidizing (O) and reducing (F) valencies of the

metal nitrate, M(NO3)2 and the fuel oxalyldihydrazide (ODH) C2H6N4O2

can be calculated as follows:

M(NO3)2, where M = Zn, Ca, Mg, Be, Ba etc.

1M = 02+

6O = 12

3 N = 00

10 –

Total oxidizing valency of the metal nitrate, M(NO3)2 = 10 –

ODH, C2H6N4O2:

2C = 08 +

6H = 06 +

2O = 04 –

4N = 00

10 +

Total reducing valency of the fuel ODH = 10 + .

Hence, for the complete combustion of M(NO3)2: ODH mixture, the

molar ratio becomes: 10/10 = 1.

The stoichiometric equation for this can be represented by Equation 3.3.

M(NO3)2(aq) + C2H6N4O2(aq) MO(s) + 2CO2(g) + 3H2O(g) +

3N2(g) ..... (3.3)

(MO = metal oxide).

60

When the reaction of the metal nitrate and ODH is carried out in

the molar ratio of 1:1, the energy released is maximum and the

combustion is completed with no carbon residue. This type of

stoichiometric balance of a redox mixture for combustion reaction is

fundamental to the synthesis of nano metal oxides by solution

combustion synthesis.

3.2.2 Characteristics of solution combustion synthesis

Some of the important characteristics of the solution combustion

synthesis are as follows:

(i) The process is simple and requires relatively simple equipment. It

is also economically attractive and easy to scale up.

(ii) Short reaction time.

(iii) The particles are in nano size and the compounds are of high

purity.

(iv) The process is fast, instantaneous and results in highly

crystalline products.

(iv) The high exothermicity of the redox mixture permits

incorporation of the desired quantity of impurity ions or

dopants in the metal oxides which dramatically change the

properties of the host metal oxides.

(v) Uniform distribution of dopants takes place throughout the host

material due to mixing of the reactants in initial solution at

61

atomic levels. Due to evolution of large volumes of gases

produced during the combustion process, nanosized,

porous and foamy product is obtained.

(vi) The temperature instantaneously rises above 1000˚C with the

flame and combustion of the fuel during the combustion

process is completed in a short period of time.

(vii) The oxide samples which are prepared by solution combustion

synthesis are highly crystalline even though they require less

energy than the solid state reaction method. Products of

virtually any size (micron to nano) and shape (spherical to

hexagonal) can be synthesized by this technique.

3.2.3 Role of fuels

Urea is an ideal fuel for the synthesis of high temperature oxides

such as alumina and alkaline earth aluminates. In case of oxides which

are unstable above 10000C, alternate fuels are employed. Hydrazine

based fuels such as carbohydrazide (CH), oxalyldihydrazide (ODH) and

malonicdihydrazide (MDH) which have low ignition temperature serve

as alternate fuels. These alternate fuels are combustible due to the

presence of N-N bond that decomposes exothermically to dinitrogen

(N2).

The fuels serve as the sources of carbon and hydrogen which on

combustion form simple gases such as carbon dioxide and water

liberating heat.

62

(i) The fuels form complexes with the metal ions which facilitate

the homogeneous mixing of cations in the solution. They break

down into the components from which they are formed.

(ii) These components in turn decompose to produce combustible

gases like HCNO, NH3 which ignite giving oxides of nitrogen

such as NO and NO2.

An ideal fuel should satisfy some of the following important criteria:

(i) It should be water soluble.

(ii) It should have low ignition temperature (less than 5000C).

(iii) It should be compatible with metal nitrates. That is the

combustion reaction should be controlled and smooth and

should not lead to explosion.

(iv) It should produce large amounts of gases which have low

molecular mass and harmless during combustion.

(v) It should not yield other residual masses except the oxide in

question.

(vi) It should be readily available or easy to prepare.

A combustion synthesis reaction is influenced by the type of fuel and

the fuel-to-oxidizer ratio. The exothermic temperature of the redox

reaction (Tad) varies from 10000C to 15000C. The nature of combustion

differs from flaming (gas phase) to non-flaming (smoldering and

heterogeneous) type depending upon the fuel used and the type of

metal ion involved. Some of the fuels are specific for particular classes

63

of compounds. For example, urea is specific for alumina and related

oxides, CH is specific for zirconia and related oxides, ODH is specific for

Fe2O3 and ferrites, tetraformaltrisazine (TFTA) for titania and realted

oxides, Glycine for chromium and related oxides etc. This specificity of

the fuels is probably controlled by the formation of the metal-ligand

complex, the thermodynamics of the reaction and also by the thermal

stability of the desired oxide formed.

From theoretical point of view, any redox mixture once ignited

undergoes combustion. All metal nitrates on pyrolysis yield the

corresponding metal oxides. The decomposition temperature of the

metal nitrates can be lowered by the addition of the fuel. The choice of

fuel is an important factor in deciding the exothermicity of the redox

reaction between the metal nitrate and the fuel. Depending upon the

exothermicity of the reaction, combustion can be smoldering, flaming or

explosive nature. It has been reported that the choice of fuel greatly

influences the combustion process. The combustion process which is

violent with a particular fuel can be controlled by using an alternative

fuel with the same metal nitrate [116-119].

3.2.4 General procedure for solution combustion synthesis

Generally, in an SCS process, stoichiometric amounts of metal

nitrates and fuels are taken in minimum quantity of double distilled

water (when both the precursor salts and the fuel are water soluble, a

64

good homogenization can be achieved in the solution) and stirred on a

magnetic stirrer to achieve uniform mixing.

In combustion preparation, hydrated metal nitrates are chosen as

the metal precursors because of the fact that the group makes

them strong oxidizing agents and highly water soluble compounds.

They also have low melting points. In the SCS process, each

atom/molecule is ionized and dissolves in distilled water forming a clear,

transparent solution. The resulting solution is transferred into a

cylindrical petri dish of approximately 300 mL capacity and heated over

a hot plate to boil off the excess water. The petri dish containing the wet

powder is introduced into a muffle furnace maintained at 300 ± 50˚C.

Initially, the wet powder undergoes thermal dehydration followed by

decomposition of the metal nitrate and fuel and then ruptures into a

flame after about 3 to 5 minutes.

The flame temperature can be measured by placing a

thermocouple inside the petri dish without touching the solution. This

temperature has been found to be around 850 ± 50˚C and persists only

for a few seconds. The resulting combustion powder occupies the entire

volume of the reaction vessel. The product is voluminous, weakly

agglomerated and nano sized with a high surface area. It is then cooled

to room temperature and ground well (Plates 3.1 to 3.4).

65

Plate 3.1 Redox mixture stirred on a magnetic stirrer

Plate 3.2 Redox mixture introduced into the muffle furnace

66

Plate 3.3 Ignition of the redox mixture

Plate 3.4 Combustion of the redox mixture

67

3.2.5 Combustion chamber

The combustion process was performed in an electric muffle furnace

(Tempo Instruments and Equipment, Mumbai). It operates on 240 volts,

13.75 ampere current. It has a power rating of 3.3 kW and an operating

volume of 35x15x15 cm3. The heating element is a Kanthal wire (Fe -

67%, Cr - 25%, Al - 5% and Co - 3%) of 18 SWG. The average heating

rate was 10°C per minute. Chromel-Alumel thermocouple (Cr-Al:

1200°C, HIMA) was used to measure the furnace temperature. A

medium sized exhaust fan for ventilating the fumes emanating from the

combustion process was positioned approximately 10 feet above the

furnace in such a way that the convection current does not affect the

combustion process.

3.3 Chemicals and reagents

Ferric nitrate, cerium nitrate, Glycine, citric acid, diethyl oxalate,

hydrazine hydrate and ethanol were obtained from sd Fine Chemicals,

India. All the chemicals were of analytical grade and were used without

further purification. Double distilled water was used throughout the

experiments.

3.4 Synthesis of α-Fe2O3 nanopowder by solution combustion

synthesis using ODH as fuel (NP1)

The starting materials used for the combustion synthesis of α-

Fe2O3 nanopowder were ferric nitrate as oxidizer and oxalyldihydrazide

68

(ODH) as fuel. The fuel ODH was prepared as follows: 146.14g of

diethyl oxalate (1 mole) was added dropwise to 100.12g of hydrazine

hydrate (2 moles) and dissolved in 225 ml of distilled water in a 1000 ml

beaker. The entire addition was carried out in an ice cold bath with

vigorous stirring. A white precipitate was obtained which was allowed to

stand overnight. It was then washed several times with ethanol, filtered

and dried [6].

5g 0f ferric nitrate, Fe(NO3)3.9H2O was taken in a petridish of

approximately 300 mL capacity and dissolved in minimum quantity of

double distilled water. 2.2g of ODH, C2H6N4O2 was added to it and the

mixture was stirred magnetically for about 10 minutes. The excess

water was evaporated by heating over a hot plate until a wet paste was

left behind. The petri dish was then introduced into a muffle furnace

maintained at about 300 to 350˚C. The reaction mixture after

undergoing thermal dehydration ignited with the liberation of gaseous

products such as oxides of nitrogen, water and carbon dioxide. The

combustion process was self propagating and within a few minutes, the

reaction was completed and a red fluffy powder was obtained. It was

cooled to room temperature and ground well. The stoichiometric

reaction between ferric nitrate and ODH can be represented by

equation 3.4.

2Fe (NO3)3(aq) + 3C2H6N4O2(aq) Fe2O3(s) + 6CO2(g) +

9H2O(g) +9N2(g)......(3.4)

69

The nanopowder thus obtained was denoted as NP1.

For the complete combustion of ferric nitrate, the O/F ratio was

maintained at 1. The reaction of ferric nitrate with ODH was carried out

in the molar ratio of 1:1.

3.5 Synthesis of α-Fe2O3 nanopowder by solution combustion

synthesis using Glycine as fuel (NP2)

The starting materials used for the combustion synthesis of α-

Fe2O3 nanopowder were ferric nitrate as oxidizer and Glycine as fuel.

5g of ferric nitrate, Fe(NO3)3.9H2O and 1.5485g of Glycine, C2H5NO2

were taken in a petridish of approximately 300 mL capacity and

dissolved in minimum quantity of double distilled water. The mixture

was stirred magnetically for about 10 minutes. The excess water was

evaporated by heating over a hot plate until a wet paste was left behind.

The petri dish was then introduced into a muffle furnace maintained at

about 300 to 350˚C. The reaction mixture after undergoing thermal

dehydration ignited with the liberation of gaseous products such as

oxides of nitrogen, water and carbon dioxide. The combustion process

was self propagating and within a few minutes, the reaction was

completed and a red fluffy powder was obtained. It was cooled to room

temperature and ground well. The stoichiometric reaction between the

ferric nitrate and Glycine can be represented by Equation 3.5.

70

2Fe (NO3)3(aq) + C2H5NO2(aq) Fe2O3(s) + 4CO2(g) +

5H2O(g) + 4N2(g) ..... (3.5)


For the complete combustion of ferric nitrate, the O/F ratio was

maintained at 1. The reaction of ferric nitrate with Glycine was carried

out in the molar ratio of 1:1.

3.6 Synthesis of CeO2 nanopowder by solution combustion

synthesis using citric acid as fuel (NP3)

The starting materials used for the combustion synthesis of CeO2

nanopowder were cerium nitrate as oxidizer and citric acid as fuel. 5g

of cerium nitrate, Ce(NO3)3·6H2O and 2.02g of citric acid, C6H8O7 were

taken in a petridish of approximately 300 mL capacity and dissolved in

minimum quantity of double distilled water. The mixture was stirred

magnetically for about 10 minutes. The excess water was evaporated

by heating over a hot plate until a wet paste was left behind. The petri

dish was then introduced into a muffle furnace maintained at about 300

to 350˚C. The reaction mixture after undergoing thermal dehydration

ignited with the liberation of gaseous products such as oxides of

nitrogen, water and carbon dioxide. The combustion process was self

propagating and within a few minutes, the reaction was completed and

a white fluffy powder was obtained. The nanopowder was then cooled

to room temperature and ground well. The stoichiometric reaction

71

between cerium nitrate and citric acid can be represented by Equation

3.6.

2Ce(NO3)3 (aq) + C6H8O7 (aq) 2CeO2 + 6CO2 (g) + 2H2O (g)

+ 3 N2 (g) ..... (3.6)


For the complete combustion of cerium nitrate, the O/F ratio was

maintained at 1. The reaction of cerium nitrate with citric acid was

carried out in the molar ratio of 1:1.

3.7 Concluding remarks

The three nanopowders NP1, NP2 and NP3 were successfully

synthesized by solution combustion synthesis. All the three

nanopowders were obtained as fine powders. The combustion process

in all the three cases was found to be complete and exothermic with no

carbon residue.

CHAPTER 4

CHARACTERIZATION OF THE NANO

METAL OXIDES

72

4.1 Characterization techniques

The as-formed nano metal oxides were characterized by

techniques such as Powder X-ray diffraction (PXRD), Fourier transform

infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), UV

– visible spectroscopy, band gap and Brunauer-Emmet-Teller (BET)

surface area measurements.

4.2 X-ray diffraction studies

X-rays are short wavelength electromagnetic radiations produced by

the deceleration of high energy electrons or by electronic transitions

involving electrons in the inner orbitals of atoms. The wavelength of X-

rays ranges from about 10–4 to 10 nm. They have high energy. They

travel in straight line and affect photographic film. X-rays have high

penetrating power. The techniques based on the measurement of

fluorescence, absorption, scattering and diffraction of X-rays are highly

useful in the investigation of the composition and structures of

materials. For analytical purposes, X-rays are obtained in three ways.

(i) By bombardment of a metal target with a beam of high energy

electrons.

(ii) By exposure of a substance to a primary beam of X-rays in order

to generate a secondary X-ray beam by fluorescence.

(iii) By using a radioactive substance whose decay process results

in X-ray emission.

73

In an X-ray tube, electrons produced at a heated cathode are

accelerated towards a metal anode (the target) by a potential as high as

100kV. When these high energy electrons strike the metal target, a part

of their energy is radiated in the form of X-rays.

4.2.1 The Laue method

The Laue method was the first diffraction method to be used. A

beam of white radiation, the continuous spectrum from an X-ray tube, is

allowed to fall on a fixed single crystal. The Bragg’s angle (θ) is

therefore fixed for every set of planes in the crystal and each set picks

out and diffracts that particular wavelength which satisfies the Bragg’s

law for the particular values of d and θ involved. Each diffracted beam

thus has a different wavelength.

4.2.2 The rotating crystal method

In the rotating crystal method, a single crystal is mounted with

one of its axes or some important crystallographic direction, normal to a

monochromatic X-ray beam. A cylindrical film is placed around it and

the crystal is rotated about the chosen direction so that the axis of the

film coincides with the axis of the crystal.

As the crystal rotates, a particular set of lattice planes will make

the correct Bragg’s angle (θ) for reflection of the monochromatic

incident beam and at that instance, a reflected beam will be formed.

The reflected beams are again located on imaginary cones but now the

cone axes coincide with the rotation axis. The result is that the spots on

74

the film, when the film is laid out flat lie on imaginary horizontal lines.

Since the crystal is rotated about only one axis, the Bragg’s angle (θ)

does not take on all possible values between 00 and 900 for every set of

planes. The rotating-crystal method and its variations are used in the

determination of unknown crystal structures.

4.2.3 The Debye-Scherer method

In the Debye-Scherer method, a narrow strip of film is curved into

a short cylinder with the specimen placed on its axis and the incident

beam directed at right angles to this axis. The Debye-Scherer and other

variations of the powder method are very widely used especially in

metallurgy. The powder method is the only method that can be

employed when a single crystal specimen is not available. This is suited

for determining lattice parameters with high precision and for the

identification of phase, whether they occur alone or in mixtures such as

polyphase alloys, corrosion products, refractories and rocks.

4.2.4 The diffractometer method

The diffractometer can be used as a tool in diffraction analysis.

This instrument is known as a diffractometer when it is used with X-rays

of known wavelength to determine the unknown spacing between the

crystal planes and as spectrometer in the reverse case, when crystal

planes of known spacing are used to determine unknown wavelengths.

The diffractometer is always used with monochromatic radiation and

75

measurements may be made on either single crystals or polycrystalline

specimens.

4.2.5 Powder X-ray diffraction method

Three types of radiations are used for crystal diffraction studies,

viz., X-rays, electrons and neutrons. Among these, X-rays are the most

useful and popular. For the investigation of crystal structures by XRD,

Bragg’s law is the most basic and important principle. According to this

approach, the crystal is considered to be made up of layers or planes

such that each layer or plane acts as a semi-transparent mirror. Some

of the X-rays are reflected off a plane with the angle of reflection equal

to the angle of incidence, but the rest are transmitted to be

subsequently reflected by the succeeding planes.

Two X-ray beams, 1 and 2 (Figure 4.1) are reflected from

adjacent planes, A and B, within the crystal and the condition under

which the reflected beams 1' and 2' are in phase has to be known. The

beam 22' has to travel the extra distance xyz as compared to the beam

11'. For the beams 1' and 2' to be in phase, the distance xyz must be

equal to an integral multiple of wavelength. The perpendicular distance

between pairs of adjacent planes, the d spacing and the angle of

incidence or Bragg’s angle (θ) are related to the distance xy by

Equation 4.1.

….. (4.1)

Thus, ….. (4.2)

76

But,

Therefore,

This is the so-called Bragg’s law. When Bragg’s law is satisfied, the

reflected beams are in phase and interfere constructively.

Figure 4.1 Scheme for the derivation of Bragg's law

Powder X-ray diffraction (PXRD) is a versatile non-destructive

technique that reveals detailed information about the chemical

composition and the crystallographic structure of both natural as well as

synthetic materials. The principle of PXRD is shown in Figure 4.2. A

monochromatic beam of X-rays strikes a finely powdered sample that

has crystals randomly arranged in every possible orientation. In such a

powdered sample, the various lattice planes are also present in every

possible orientation. For each set of planes, therefore, at least some

crystals must be oriented at the Bragg’s angle (θ) to the incident beam

77

and hence, diffraction occurs for these crystals and planes. The

diffracted beams may be detected using a Geiger counter or scintillation

counter connected to a computer (diffractometer). The computer then

plots the characteristic XRD pattern of the measured sample upon the

detected X-ray intensities on different positions. This pattern can be

further used to determine the crystal structure and other structural

features of the specimen [120].

Figure 4.2 Schematic diagram of the setup for PXRD

The as-prepared metal oxide nano powders were identified by

PXRD method. The measurements were performed on a Philips X-ray

diffractometer (PW/1050/70/76) using Cu Kα radiation (λ = 1.542A°) at

30 kV and 20 mA with Ni filter. The fine powder of nano metal oxide (<

100 µm) was placed on a glass specimen holder and pressed using a

glass slide. All the samples were scanned between 10° < 2θ < 70° at a

speed of 2° per minute. The peaks thus obtained were identified using

78

the Hanawalt search interpretation method to determine the crystalline

phases present in the sample. The interplanar distances (‘d’ spacings)

were evaluated using Equation 4.4.

222 lkh

ad

++= ….. (4.4)

‘a’ refers to the lattice parameter, and h, k, l are the crystalline face

indices while d is the crystalline face space.

It is known that X-ray diffraction line broadening is influenced by

the crystallite size and the internal strains. The average crystallite size

was determined by applying Scherer’s formula (Equation 4.5) to the full

width at half maximum (FWHM) of the highly intense peak [121].

θβλ

cos

9.0=D ….. (4.5)

where β is FWHM (rad), λ is wavelength of X-rays (nm) and θ is the

diffraction angle (degrees).

Figure 4.3 shows the PXRD pattern of the nanopowder NP1. The

peaks at (012), (104), (110), (113), (024), (116), (018), (214) and (300)

correspond to the rhombohedral phase of α-Fe2O3 (JCPDS file

number:87-1165) with a = 5.035 Å, c = 13.749 Å. The diffracted patterns

are well matching with the literature [122]. No impurity peaks and other

possible phases of iron oxide were observed. Further, the strong and

sharp diffraction peaks indicated higher degree of crystallinity of the

product. The average crystallite size was found to be around 44nm.

79

10 20 30 40 50 60 70

0

500

1000

1500

2000

2500

(300)(214)

(018)

(116)

(024)

(113)

(110)

(104)

Inte

nsity

(a.

u.)

2θ (degrees)

(012)

Figure 4.3 PXRD pattern of the nanopowder NP1


diffraction peaks at (012), (104), (110), (113), (024), (116), (018), (214)

and (300) correspond to the rhombohedral phase of α-Fe2O3 (JCPDS

file number: 87-1165) with a = 5.035 Å, c = 13.749 Å. The diffraction

patterns correspond to the one reported in literature [123]. No impurity

peaks and other possible phases of iron oxide were observed. Further,

the strong and sharp diffraction peaks indicated higher degree of

crystallinity of the product. The average crystallite size was found to be

around 30nm.

80

10 20 30 40 50 60 70

0

500

1000

1500

2000

2500

Inte

nsity

(a.

u.)

2θ (degrees)

(300)

(018)

(214)

(116)

(024)

(113)

(110)

(104)

(012)



diffraction peaks at (111), (200), (220), (311), (222) and

(400)correspond to the face centered cubic phase of CeO2(JCPDS file

number: 81-0792) with a = 5.4090 Å, c = 13.749 Å. The diffraction

patterns correspond to the one reported in literature [124]. No impurity

peaks and other possible phases of CeO2 were observed. Further, the

strong and sharp diffraction peaks indicated higher degree of

crystallinity of the product. The average crystallite size was found to be

around 14nm.

81

10 20 30 40 50 60 70

0

50

100

150

200

250

Inte

nsity

(a.

u.)

2θ (degrees)

(400)

(200)

(220)

(222)

(311)

(111)


The grain size of the nanopowders was estimated from the

powder X-ray diffraction line broadening ( ) using the analysis

described by Williamson and Hall (W–H) method. The W-H relation

(Equation 4.6) can be written as:

….. (4.6)

where β is FWHM (rad) ε is the strain developed, θ is the diffraction

angle, λ is the wavelength of X-rays used and D is the grain size.

(FWHM in radian) is measured for different XRD lines corresponding

to different planes. The Equation 4.6represents a straight line between

4sinθ (X-axis) and βcosθ (Y-axis). The slope of line gives the

inhomogeneous strain (ε) and intercept (λ/D) of this line on the Y-axis

gives grain size (D).

The W-H plots of the three nanopowders NP1, NP2 and NP3 are

shown in Figures 4.6, 4.7 and 4.8 respectively.

82

0.8 1.0 1.2 1.4 1.6 1.80.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

(116)(024)

(110)(104)

β co

s θ

4 sin θ

(hkl) α - Fe2O

3

Linear Fit

(012)

Figure 4.6 W-H plot of the nanopowder NP1

0.8 1.0 1.2 1.4 1.6 1.8 2.00.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

(116)

(024)

(110)

(104)

β co

s θ

4 sin θ

(012)


83

1.0 1.5 2.0 2.5 3.0 3.5 4.00.0095

0.0100

0.0105

0.0110

0.0115

β co

sθ

4 sinθ


The mean crystallite size of the three nanopowders determined

from W–H method is slightly different from those calculated using

Debye-Scherer’s method. The small variation in the values can be

attributed to the fact that in Scherer’s formula, the strain component is

assumed to be zero and observed broadening of the diffraction peak is

considered as a result of reducing grain size only.

In order to estimate the actual cell parameters Rietveld

refinement was performed on the three nanopowders. In the Rietveld

refinement method, the profile intensities obtained from step-scanning

measurements of the powders are used to estimate an approximate

structural model for the real structure. In our work, the Rietveld

refinement was performed through the FULLPROF program [125]. The

pseudo-voigt function was used to fit the several parameters to the data

point: one scale factor, one zero shifting, four back ground, three cell

84

parameters, five shape and width of the peaks, one global thermal

factors and two asymmetric factors.

Figure 4.9 represents the experimental and calculated PXRD

patterns of the nanopowder NP1 obtained by the Rietveld refinement.

The packing diagram of the nanopowder after Rietveld refinement is

shown in Fig. 4.10. The refined parameters such as occupancy and

atomic functional positions of the α-Fe2O3 nanopowder are summarized

in Table 4.1. The fitting parameters (Rp, Rwp and χ2) indicate a good

agreement between the refined and observed PXRD patterns for the α-

Fe2O3 nanopowder.

Figure 4.9 Rietveld analysis of the nanopowder NP1

85

Figure 4.10 Packing diagram of the nanopowder NP1

Table 4.1. Rietveld refined structural parameters for nanopowder NP1 Atoms Oxidation

State

Wyckoff

Notation

Positional parameters Biso Occupancy

x y z

Fe1 +3 12c 0.0000 0.0000 0.3551(2) 0.10 1

O1 -2 18e 0.3113(9) 0.0000 0.2500 0.50 1

Crystal system = Hexagonal, Lattice parameter, a = 5.037(5) Å, c =

13.757(9) Å, Cell Volume = 302.36(4) Å3. Space group = R -3c(167)

RFactor; Rp = 0.824, Rwp = 0.12, RBragg = 0.035, RF = 0.029.

Figure 4.11 represents the experimental and calculated PXRD

patterns of the nanopowder NP2 obtained by using the Rietveld

method. The packing diagram of the nanopowder after Rietveld

refinement is shown in Fig. 4.12. Table 2 gives a summary of the

86

refined parameters such as occupancy and atomic functional positions

of the α-Fe2O3 nanopowder. The fitting parameters (Rp, Rwp and χ2)

indicate a good agreement between the refined and observed PXRD

patterns for the α-Fe2O3 nanopowder.


Figure 4.12 Packing diagram of the nanopowder NP2

87

Table 4.2. Rietveld refined structural parameters for nanopowder NP2

Atoms Oxidation

State

Wyckoff

Notation


x y z

Fe1 +3 12c 0.0000 0.0000 0.3551(2) 0.10 1

O1 -2 18e 0.3113(9) 0.0000 0.2500 0.50 1

Crystal system = Hexagonal, Lattice parameter, a = 5.037(5) Å, c =

13.757(9) Å, Cell Volume = 302.36(4) Å3. Space group = R -3c(167)

RFactor; Rp = 0.824, Rwp = 0.12, RBragg = 0.035, RF = 0.029.

The experimental and calculated PXRD patterns of the

nanopowder NP3 obtained by using the Rietveld method are shown in

Figure 4.13. The packing diagram of the nanopowder after Rietveld

refinement is shown in Fig. 4.14. Table 3 gives a summary of the

refined parameters such as occupancy and atomic functional positions

of the CeO2nanopowder. The fitting parameters (Rp, Rwp and χ2)

indicate a good agreement between the refined and observed PXRD

patterns for the CeO2 nanopowder.


88

Fig. 4.14 Packing diagram of the nanopowder NP3

Table 4.3. Rietveld refined structural parameters for nanopowder NP3

Atoms Oxidation State

Wyckoff Notation


x y z

Ce 1 +4 4a 0.0000 0.0000 0.0000 0.050 1

O 1 -2 8c 0.2500 0.2500 0.2500 0.500 1

Crystal system = Cubic; Lattice parameter, a = 5.406(3) Å,

Space group = Fm-3m (225); R Factors; Rp = 0.129, Rwp = 0.179,

RBragg = 0.052, RF = 0.032.

4.3. Fourier transform infrared spectroscopy

Infrared spectroscopy is an important technique in material

analysis. Fourier transform infrared spectroscopy (FTIR) is the preferred

method of infrared spectroscopy. When infrared radiation is passed

through a sample, some of the infrared radiation is absorbed by the

89

sample and some of it is transmitted. The resulting spectrum represents

the molecular absorption and transmission, creating a molecular

fingerprint of the sample. Like a fingerprint, no two unique molecular

structures produce the same infrared spectrum. This makes infrared

spectroscopy a useful tool for several types of analyses.

FTIR provides the following information:

(i) Identification of unknown materials.

(ii) Determination of the quantity of consistency of the sample.

(iii) Determine the amount of different components in a mixture.

The original infrared instruments were of the dispersive type.

These instruments separated the individual frequencies of the energy

emitted from the infrared source. This was accomplished by the use of a

prism or grating. An infrared prism works exactly in the same way as a

visible prism which separates visible light radiations based on their

frequencies. A grating is a more modern dispersive element which

separates the infrared radiations of different frequencies in a better way.

The detector measures the amount of energy at each frequency which

has passed through the sample. This results in a spectrum which is a

plot of intensity versus frequency.

FTIR was developed in order to overcome the limitations

encountered with dispersive instruments. The main difficulty was the

slow scanning process. A method for measuring all of the infrared

frequencies simultaneously rather than individually was needed. A

90

solution was developed which employed a very simple optical device

called an interferometer. The interferometer produces a unique type of

signal, which has all of the infrared frequencies “encoded” into it. The

signal can be measured very quickly usually in the order of one second

or so. Thus the time element per sample is reduced to a matter of a few

seconds rather than several minutes.

Fourier transform infrared spectroscopy is preferred over

dispersive or filter methods of infrared spectral analysis for several

reasons. Some of these are as follows:

(i) It is a non-destructive technique.

(ii) It provides a precise measurement method which requires no

external calibration.

(iii) It can increase speed, collecting a scan every second.

(iv) It can increase sensitivity – one second scan can be co-added

together to ratio out random noise.

(v) It has greater optical throughput.

(vi) It is mechanically simple with only one moving part.

The FTIR spectra of the as prepared metal oxide nanopowders

were recorded using Nicollet IMPACT 400 D FTIR spectrometer from

4000 to 300 cm–1 using KBr as the reference sample.

Figure 4.15 represents the FTIR spectrum of the nanopowder

NP1. The spectrum showed the two intense absorption bands at around

537 and 450 cm-1. These vibrations could be attributed to the

91

characteristic absorption bands of the Fe-O bond. The weak absorption

band at around 3400 cm-1 was characteristic of H-O-H bending of the

H2O molecules revealing the presence of hydroxyl groups in the as

formed sample [126].

500 1000 1500 2000 2500 3000 3500 4000

20

30

40

50

60

70

(450)

Wavenumber (cm-1)

% T

rans

mitt

ance

(a.

u.)

(3400)

(537)

Fig. 4.15 FTIR spectrum of the nanopowder NP1

The FTIR spectrum of the nanopowder NP2 is shown in Figure

4.16. The absorption bands at around 537 and 450 cm-1 correspond to

the characteristic vibrations of the Fe-O bond. A weak absorption band

at around 3400 cm-1 could be attributed to the characteristic H-O-H

bending vibrations of the H2O molecules revealing the presence of

hydroxyl groups in the as formed sample [127].

92

500 1000 1500 2000 2500 3000 3500 4000

20

30

40

50

60

70

(450)

Wavenumber (cm-1)

% T

rans

mitt

ance

(a.

u.)

(3400)

(537)


Figure 4.17 shows the FTIR spectrum of the nanopowder NP3. A

strong absorption band was observed at around 554 cm−1 which is the

characteristic stretching vibration of the Ce–O bond. Two weak

absorption bands at around 3400 and 1600 cm−1 were observed in the

FTIR spectrum. These absorption bands were attributed to the

characteristic absorption bands of the hydroxyl group of water and CO2

absorbed from the environment on the surface of the nanopowder due

to its high surface-to-volume ratio [128].

0 500 1000 1500 2000 2500 3000 3500 40000

20

40

60

80

100

% T

rans

mitt

ance

(a.

u.)

Wavenumber (cm -1)

(3400)(1600)

(554)


4.4 Scanning electron microscopy

93

Electron microscopy is an extremely versatile technique which

provides structural information over a wide range of resolution ranging

from 10 µ to 2 Å. This technique is especially employed in the range

where the specimen is so small (<1µm) that optical microscopes are not

able to image it anymore.

Electron microscopes operate in either transmission (TEM) or

reflection (SEM) mode. The path of the electron beam within the

scanning electron microscope differs from that in the transmission

electron microscope. This method is depiction of preparations with

conductive surfaces. Scanning electron microscopy is well suited for

very low magnifications.

In a scanning electron microscope, the surface of the object is

scanned with the electron beam point by point whereby secondary

electrons are set free. The number of secondary electrons is dependent

on the angle of inclination between the incident electron beam and the

surface of the object. The secondary electrons are collected by a

detector that is positioned at an angle at the side above the object. The

signal is then enhanced electronically. The magnification can be chosen

smoothly (depending on the model) and the image appears a little later

on a viewing screen. SEM micrographs give information about the

particle size, morphology, size and distribution of grains in the sample.

94

The SEM micrographs of the as-prepared nanopowders were

recorded using JEOL (JSM-840A) scanning electron microscope.

Figure 4.18 shows the SEM micrograph of nanopowder NP1. The

particles were found to be dumbbell in shape. The particles were

voluminous with high degree of agglomeration.

Figure 4.18 SEM micrograph of the nanopowder NP1

The SEM micrograph of nanopowder NP2 (Figure 4.19) indicated

that the particles were found to be dumbbell in shape. The particles

were voluminous and exhibited high degree of agglomeration.

95

Figure 4.19 SEM micrograph of the nanopowder NP2 Figure 4.20 shows the SEM micrograph of nanopowder NP3. The

nanoparticles were found to be agglomerated, fluffy and plate like

clusters in nature.

Figure 4.20 SEM micrograph of the nanopowder NP3

It was found that, in case of all the three nanopowders, the

particles were agglomerated. The SEM micrographs indicated high

degree of porosity. In case of combustion method, it is well known that

96

the morphological features of the prepared nanopowder are strongly

dependent on the heat and gases generated during the complex

decomposition. Large amount of gases are suitable for preparation of

tiny particles while the heat released is an important factor for crystal

growth. The agglomeration of nanoparticles is usually explained as a

common way to minimize their surface free energy. [129, 130].

4.5 UV-visible spectroscopy and band gap measurements

The band gap energy (Eg) is an important feature of

semiconductors which determines their usefulness in optoelectronic

devices. This technique is frequently employed for the characterization

of semiconductor thin films. Due to low scattering in solid films, it is easy

to extract the band gap energy (Eg) values from their absorption spectra

by knowing their thickness. In case of colloidal samples, the scattering

effect is enhanced since more superficial area is exposed to the light

beam. In the case of normal incidence mode, the dispersed light is

counted as absorbed light and hence this technique (optical absorption)

does not distinguish between the two phenomena. On the other hand, it

is common to obtain powdered samples instead of thin films or colloids,

and frequently UV-visible absorption spectroscopy is carried out by

dispersing the sample in a liquid medium such as water, ethanol or

methanol. If the particle size of the sample is not small enough, it

precipitates and the absorption spectrum is even more difficult to

interpret.

97

To reveal the electronic structure and size effect, the UV–visible

absorption measurement of the as-prepared nanopowders were

conducted at room temperature. The UV–visible absorption spectra of

the samples were recorded from 190 to 1100 nm using ELICO SL 159

UV–visible spectrophotometer.

The UV-visible spectrum of nanopowder NP1 is shown in Figure

4.21. The absorption between 250 and 350 nm centered at 300 nm

(region 1) and the broad absorption between 400 and 600 nm with a

peak at 540nm (region 2) were observed in the spectrum. The first

region results mainly from the ligand to metal charge transfer transitions

and partly from the contribution of the Fe3+ ligand field transitions

6A1→4T1 (

4P). In the second region the absorption peaks were mainly

due to the 6A1 + 6A1→4T1 (4G) + 4T1 (4G) excitation of an Fe3+–Fe3+ pair,

which possibly overlapped the contributions of 6A1→4E, 4A1 (4G) ligand

field transition and the charge-transfer band tail [131]. Similar results

have been observed by Xu et al. [132] in α-Fe2O3 nano leaves

synthesized by oxygenating pure iron. Further, Zhang et al. [133]

recorded the absorption spectrum of α-Fe2O3 nanoparticles suspended

in ethanol. The absorption bands at 310 and 414 nm were assigned to

the 6A1→4T1 (

4P) and 6A1→4T2, while the absorption bands in the visible

region near 580 nm and 681 nm were assigned to the 6A1 + 6A1→4T1

(4G) + 4T1(4G) double exciton process (DEP) and 6A1→

4T2 (4G) ligand

field transitions of Fe3+ respectively. Further, with decreasing size, the

98

absorption band for DEP showed blue shift to 580 nm which indicated

that the increase in particle size leads to red shift.

200 400 600 800 1000

0.5

1.0

1.5

2.0

Abs

orba

nce

(a.u

.)

Wavelength (nm)

300540

Lamp change over

Figure 4.21 UV–visible spectrum of the nanopowder NP1

Figure 4.22 shows the UV-visible spectrum of nanopowder NP2.

The UV-visible spectrum exhibited two absorption regions, one between

250 and 350 nm centered at 300 nm (region 1)and the other between

400 and 600 nm with a peak at 540 nm (region 2). The first region

resulted mainly from the ligand to metal charge transfer transitions and

partly from the contribution of the Fe3+ ligand field transitions 6A1→4T1

(4P). The second region exhibited absorption peaks which were mainly

due to the

6A1 + 6A1→4T1 (4G) + 4T1(4G) excitation of an Fe3+–Fe3+ pair, which

possibly overlapped the contributions of 6A1→4E, 4A1(4G) ligand field

transition and the charge-transfer band tail. The absorption bands at

310 and 414 nm could be assigned to the 6A1 → 4T1(4P) and 6A1 → 4T2.

On the other hand, the absorption bands in the visible region near 580

99

nm and 681 nm could be assigned to the 6A1 + 6A1→4T1 (

4G) + 4T1 (4G)

double exciton process (DEP) and 6A1 → 4T2 (4G) ligand field transitions

of Fe3+ respectively. It was also observed that, with decrease in size,

the absorption band for DEP exhibited blue shift to 580 nm which

indicated that the increase in particle size leads to red shift [131-133].

200 300 400 500 600 700 800 900 1000 11000.0

0.5

1.0

1.5

2.0540

Abs

orba

nce

(a.u

.)

Wavelength (nm)

300

Lamp change over


The UV-visible spectrum of nanopowder NP3 is shown in Figure

4.23. The spectrum exhibits a well-defined absorption band at 298 nm

which confirmed that CeO2 nanoparticles were optically and photo-

catalytically active. Usually peak at 298 nm corresponds to the fluorite

cubic structure of CeO2. A strong absorption at around 390 nm was

observed which exhibited 10 nm blue-shift relative to the bulk material

(400 nm). It was concluded that the obvious UV-absorption for ceria

originated from charge-transfer between the O 2p and Ce 4f states in

O2− and Ce4+ [134].

100

200 400 600 800 1000

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

390

Abs

orba

nce

(a.u

)

Wavelength (nm)

298

Lamp change over


4.5.1 Direct band gap

The direct energy band gap (Ed) values of the three nanopowders

were estimated by fitting the absorption data in Equation 4.7 known as

the direct transition equation [135].

….. (4.7)

where ‘α’ is optical absorption co-efficient, ( ) is the photon energy, Ed

is the direct band gap and ‘A’ is constant. is plotted as a function

of photon energy ( ). The linear portion of the curve was extrapolated

to meet the photon energy axis. From the intersection of the

extrapolated linear portion, the direct band gap values of the

nanopowders were estimated.

Figure 4.24 shows the plot for determination of Ed of the

nanopowder NP1. The direct band gap energy value of the nanopowder

101

was found to be 2.79 eV. This value matched well to the one reported in

literature [136].

1 2 3 4 50

1x108

2x108

3x108

4x108

5x108

(αhυ

)2 (eV

cm-1)2

hυ (eV)

Ed=2.79 eV

Figure 4.24 Direct band gap energy of the nanopowder NP1


nanopowder NP2. The direct band gap energy value of the nanopowder

was found to be 2.22 eV which well matched with the one reported in

literature [136].

1 2 3 4 50.0

2.0x1010

4.0x1010

6.0x1010

8.0x1010

1.0x1011

1.2x1011

1.4x1011

1.6x1011

1.8x1011

(αhυ

)2 (eV

cm

-1)2

hυ (eV)

Ed= 2.22 eV


102


nanopowder NP3. The value of the Ed as determined from the plot was

found to be 3.12 eV. This value was found to be closer to the one

reported in literature for CeO2 [137].

1.0 1.5 2.0 2.5 3.0 3.5 4.00.0

5.0x108

1.0x109

1.5x109

2.0x109

2.5x109

3.0x109

3.5x109

4.0x109

( αα ααh

υυ υυ )2 (

cm-1

eV)2

hυ (υ (υ (υ (eV)

Eg= 3.12 eV


4.5.2 Indirect band gap

The indirect band gap (Ei) values of the three nanopowders were

estimated using Equation 4.8.

….. (4.8)

where Ei is the band gap energy for indirect transitions, Ep the phonon

energy, k is the Boltzmann constant, is the photon energy and T the

absolute temperature.

was plotted as a function of . The linear portion of the

graph was extrapolated to meet the x-axis. The energy corresponding to

the point of intersection gives the value of Ei.

103

Figure 4.27 shows the plot for determination of Ei of the

nanopowder NP1. The value of Ei was found to be 2.26 eV.

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0

10

20

30

40

50

60

70

( α)1/

2 (cm

-1)1/

2

hυ (eV)

Ei=2.26 eV

Figure 4.27 Indirect band gap energy of the nanopowder NP1

The plot for the determination of Ei of the nanopowder NP2 is

shown in Figure 4.28. The value of Ei was found to be 2.1 eV.

1 2 3 4 50

50

100

150

200

250

300

(α)1/

2 (cm

-1)1/

2

hυ (eV)

Ei=2.1 eV


Figure 4.29 shows the plot for determination of Ei of the

nanopowder NP3. The value of Ei was found to be 2.82 eV.

104

1 2 3 40

20

40

60

80

100

120

αα αα1/

2 (cm

-1/2)

hυ υ υ υ (eV)

Eg = 2.82 eV


Table 4.4 gives the summary of the band gap energy values of

the three nanopowders.

Table 4.4 Band gap energy values of the three nanopowders.

Sl. No.

Name of the nanopowder

Fuel Designation Band gap energy (eV)

Direct Indirect

1. α-Fe2O3 ODH NP1 2.79 2.26

2. α-Fe2O3 Glycine NP2 2.22 2.10

3. CeO2 Citric acid NP3 3.12 2.82

4.6 BET surface area

The Brunauer-Emmet-Teller (BET) surface areas of the three

nanopowders were determined using the instrument MICROMERITICS

GEMINE 2375. Nitrogen gas was allowed to be adsorbed on the

nanopowder at 77 K. Prior to the analysis, the nanopowders were out

gassed in an evacuation chamber at a temperature of 523 K under a

105

vacuum of 10-6Torr for 12 hours. The specific surface area values of the

three nanopowders were derived from the isotherm using BET method

in the relative pressure range, p/p0 (p is the adsorption pressure and p0

is the saturation vapour pressure), of 0.05 and 0.3 where the monolayer

coverage was assumed to be completed. The total pore volume was

calculated from the amount adsorbed (liquid volume of nitrogen) at a

relative pressure of 0.99 atm. The nitrogen adsorption and desorption

isotherms were used to determine parameters like surface area, pore

volume and pore size [138, 139].

The nitrogen adsorption desorption isotherms for determination of BET

surface area values of the three nanopowders are given in Figures 4.30

to 4.32. Table 4.5 gives the values of the BET surface area of the

nanopowders. From Table 4.5 it can be concluded that the surface area

followed the order:

NP3 > NP2 > NP1

0.0 0.2 0.4 0.6 0.8 1.00

50

100

150

200

Qua

ntity

ads

orbe

d (c

m3 g-1

)

Relative Pressure (P/P0)

Figure 4.30 BET surface area of the nanopowder NP1

106

0.0 0.2 0.4 0.6 0.8 1.0

0

5

10

15

20

25

30

35

Qua

ntity

ads

orbe

d (c

m3 g-1

)

Relative Pressure (P/P0)


s

0.0 0.2 0.4 0.6 0.8 1.00

2

4

6

8

10

12

14

16

Qua

ntity

ads

orbe

d (c

m3 g-1

)

Relative pressure (P/P0)


Table 4.5 BET surface area values of the three nanopowders

Sl. No.

Name of the nanopowder

Fuel Designation BET surface area (m2 g-1)

1. α-Fe2O3 ODH NP 1 40

2. α-Fe2O3 Glycine NP 2 45

3. CeO2 Citric acid NP 3 65

107


The three nanopowders were successfully characterized by

powder X-ray diffraction (PXRD), Fourier transform infrared

spectroscopy (FTIR), Scanning electron microscopy (SEM), UV – visible

spectroscopy, band gap and Brunauer-Emmet-Teller (BET) surface

area measurements. The PXRD pattern of the nanopowders indicated

that the powders exhibited high degree of crystallinity with no impurities

which is one of the advantages of the solution combustion method. The

mean crystallite size of the powders was in nanometer range and

followed the order: NP1 > NP2 > NP3. The band gap measurements

indicated that all the three nanopowders could act as photocatalyst. The

surface area of the nanopowders followed the order:

NP3 > NP2 > NP1.

CHAPTER 5

PHOTOCATALYTIC ACTIVITY

108

5.1 Introduction

The three nanopowders were used as photocatalysts for the

removal of three dyes viz., methyl orange (MO), rhodamine B (RhB) and

methylene blue (MB) from their aqueous solutions.

5.2 Electronic structure of a semiconductor

The linear combination of atomic orbitals results in the formation

of molecular orbitals. The number of molecular orbitals formed is equal

to the number of atomic orbitals that take part in the combination. When

N atoms are used, N molecular orbitals are formed. In case of solids, N

is very large, resulting in a large number of molecular orbitals. The

overlap of a large number of orbitals leads to molecular orbitals that are

closely spaced in energy and hence form a virtually continuous band.

The overlap of the lowest unoccupied molecular orbitals (LUMO) results

in the formation of a conduction band and a valence band is formed

from the overlapping of the highest occupied molecular orbitals

(HOMO). The band separation is known as the band gap (Eg), a region

devoid of energy levels [140, 141].

5.3 Mechanism of photocatalysis

Metal oxide semiconductors have attracted a great deal of

interest in the past decade due to their environmental applications such

as air purification and water remediation [142, 143]. The term

photocatalysis is used to describe the processes that a semiconducting

material TiO2, ZnO, Fe2O3, CeO2, SnO2 etc. undergoes when irradiated

109

by radiation whose energy is greater than its band gap energy. It is a

term that implies photon assisted generation of catalytically active

species. When the semiconductor is photoactivated, an electron-hole

pair is produced that reacts with the adsorbed species to produce

radical species. These radicals are powerful oxidizing agents and

oxidize the organic contaminants to CO2 and H2O.

The photoactivation of a semiconductor excites an electron from

the valence band to the conduction band resulting in the formation of a

positive hole (h+VB) in the valence band (Figure 5.1). The charge carriers

can be trapped in the semiconductor lattice or they can recombine,

dissipating energy [144].

Figure 5.1 Mechanism of photocatalysis

Alternatively, the charge carriers can migrate to the catalyst

surface and initiate redox reactions or the dye degradation reactions

[145]. The positive holes generated by light are trapped by H2O

110

adsorbed on the surface of the photocatalyst. The H2O gets oxidized by

h+VB producing H+ ions and OH• radicals (Equation. 5.1), which are

extremely powerful oxidants.

H2O + h+VB → •OH + H+….. (5.1)

The hydroxyl radicals subsequently oxidize organic species from

the surrounding environment to CO2 and H2O (Equation. 5.2) and in

most cases these are the most important radicals formed in most of the

cases of photocatalysis [146].

•OH + VOC → H2O + CO2 ….. (5.2)

The electrons in the conduction band can be rapidly trapped by

molecular oxygen adsorbed on the surface of the semiconductor

particle. The trapped molecular oxygen will be reduced by the excited

electrons to form superoxide (O2-•) radicals (Equation 5.3) which can

further react with H+ ions (Equation 5.4) to generate the peroxide

radicals (•OOH) and H2O2 (Eqn. 5.5). The superoxide and peroxide

radicals react with the volatile organic compounds (Equations 5.6 and

5.7) to produce CO2 and H2O [147].

O2 + e-CB → O2

-• ….. (5.3)

O2-• + H+

→ •OOH ….. (5.4)

•OOH + •OOH → H2O2 + O2 ….. (5.5)

O2-• + VOC → CO2 + H2O ….. (5.6)

•OOH + VOC → CO2 + H2O ….. (5.7)

(VOC = Volatile organic compounds)

The efficiency of a photocatalyst depends not only on its

electronic properties, but also on the availability of active sites on its

111

surface [148]. A photocatalyst can produce an infinite amount of

oxidizing species to no effect unless the resulting radicals migrate to its

surface where they can initiate the oxidation of the organic species from

the surrounding environment [149]. Apart from this, the properties such

as crystal size and structure, pore size/volume, density of the OH

groups, surface charge, number and nature of trap sites and

adsorption/desorption characteristics also influence the efficiency of the

photocatalyst.

Large surface areas result in an increase in the number of active

degradation sites available for degradation reactions. A delicate balance

between the surface area and recombination has to be achieved in

order to produce an effective photocatalyst. The photocatalytic

efficiency of the semiconductors is also affected by the surface hydroxyl

groups present in the material. These surface hydroxyl groups

participate in the photocatalytic process in a number of ways. They trap

the photoexcited electrons producing OH• radicals. They can also act as

active adsorption sites for pollutants [150-152].

5.4 Photoreactor and cell

The photodegradation experiments were carried out in a reaction

cell of circumference 25.2 cm and 500 mL capacity with an exposure

area of about 50.3 cm2. The light source was a medium pressured 125

Watt mercury vapor lamp with wavelength peaks around 350 to 400

nanometers. The photoflux as determined by ferrioxalate actinometry

112

was found to be 7.75 mW/cm2. The photoreaction experiments were

performed by direct exposure into the reaction mixture. The

experiments were performed at room temperature. The distance

between the photoreactor and the lamp housing was 27 cm.

5.5 General procedure for photocatalytic activity

The photodegradation experiments were carried out under

ultraviolet light [153]. The experiments were carried out as follows. 50

mL of the dye solution was taken in a 500 mL reaction vessel. A known

mass of the nanopowder (photocatalyst) was added to it. The solution

was stirred magnetically under ultraviolet light for a known period of

time. It was then centrifuged at around 3000 rpm for 10 minutes using

REMI C8C centrifuge. The UV-visible spectrum was recorded in the

wavelength range of 190 to 900 nm using ELICO SL 159 UV-visible

spectrophotometer. The percentage dye removal was calculated using

Equation 5.8.

….. (5.8)

where Ai and At refer to the absorbance of the dye solution before and

after photocatalysis.

5.6 Effect of variable factors

The effect of two variable factors viz., dosage of the photocatalyst

and irradiation time on the photocatalytic degradation of the dyes was

studied.

113

5.6.1 Effect of dosage of the photocatalyst

Catalyst dosage is one of the important parameters in

photocatalysis. A higher dosage of the photocatalyst increases the

percentage dye degradation by providing a larger surface area for the

adsorption of dye molecules. However, a very high catalyst dosage is

not recommended. In order to study the effect of dosage of the

photocatalyst, 50 mL of the dye solution was taken in a 500 mL reaction

vessel. A known mass of the nanopowder (photocatalyst) was added to

it. The solution was stirred magnetically under ultraviolet light for about

30 minutes. It was then centrifuged and the UV-visible spectrum was

recorded.

The experiment was conducted by varying the dosage of the

photocatalyst in increments of 10 mg. In each case, the UV-visible

spectrum was recorded from which the percentage dye removal was

calculated. A graph of the percentage dye removal against the dosage

of the photocatalyst was plotted from which the optimum photocatalyst

dosage was determined.

5.6.2 Effect of irradiation time

Once the optimum dosage of the photocatalyst was determined,

the effect of irradiation time was studied. Irradiation time is also an

important parameter in which affects the process of photocatalysis. In

order to study the effect of irradiation time on the rate of photocatalysis,

50 mL of the dye solution was taken in a 500 mL reaction vessel and

114

optimum amount of the photocatalyst was added to it. The solution was

stirred magnetically under ultraviolet light for a known period of time.

After every 5 minutes, a small aliquot of the reaction mixture was taken

out, centrifuged and the UV-visible spectrum was recorded. A graph of

the percentage dye removal against the irradiation time was plotted

from which the optimum irradiation time was determined.

5.7 Photocatalytic removal of methyl orange dye

The structure of methyl orange is shown in Figure 5.2. It is a an

anionic azo dye used in many process industries such as dyeing, paper

and pulp processing and printing textiles. The molecular formula of MO

is C14H14N3NaO3S and molecular mass is 327.33 gmol-1. Chemically,

MO is sodium4-[(4-dimethylamino)phenyldiazenyl] benzenesulfonate.

It is often used in titrations because of its clear and distinct colour

change. MO is a major water pollutant in textile and paper and pulp

industries. It is known to possess mutagenic effects. Figure 5.3 shows

the absorbance spectrum of methyl orange. The dye shows maximum

absorbance at 507 nm.

Figure 5.2 Structure of methyl orange dye

115

200 300 400 500 600 700 800 900

0.00

0.15

0.30

0.45

0.60

Abs

orba

nce

Wavelength (nm)

Figure 5.3 Absorbance spectrum of methyl orange dye

5.7.1 Preparation of the dye solution

The concentration of methyl orange dye used in all the

photocatalytic experiments was 20 ppm. 1 g of the dye stuff was

transferred to a 1000 mL volumetric flask and dissolved in little quantity

of double distilled water. It was then diluted upto the mark with double

distilled water to give a stock solution of concentration 1000 ppm. The

stock solution was appropriately diluted with double distilled water to

give a concentration of 20 ppm.


The removal of MO by NP1 was studied by varying the dosage of

the photocatalyst and the irradiation time.

116

5.8.1 Effect of dosage of the photocatalyst on the removal of

MO by NP1

The effect of dosage was studied by varying the amount of the

photocatalyst from 0.2 to 2.0 g per litre of the dye solution. From Table

5.1 and Figure 5.4 the optimum dosage was found to be 1.8 gL-1. The

dye removal at this optimum dosage was 80.43%. Beyond the optimum

dosage, the dye removal was negligible.

Table 5.1 Effect of dosage of the photocatalyst on the photocatalytic

removal of MO by NP1.

Sl. No.

Dosage of the Photocatalyst (gL-1)

Percentage Dye Removal

1. 0.2 27.39

2. 0.4 39.52

3. 0.6 49.92

4. 0.8 58.86

5. 1 66.92

6. 1.2 72.99

7. 1.4 77.56

8. 1.6 80.21

9. 1.8 80.43

10. 2 80.51

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL-1) Figure 5.4 Effect of dosage photocatalyst on the photocatalytic

117

removal of MO by NP1

5.8.2 Effect of irradiation time on the photocatalytic removal

of MO by NP1

The effect of irradiation time was studied by keeping the amount of

photocatalyst fixed (optimum dosage) and varying the irradiation time

from 5 minutes to 120 minutes as descried earlier (Section 5.6.2). From

Table 5.2 and Figure 5.5 the optimum irradiation time was found to be

50 minutes. The percentage dye removal at the optimum irradiation time

was found to be 83.02. Beyond 50 minutes the dye removal was found

to be negligible.

Table 5.2 Effect of irradiation time on the photocatalytic removal

of MO by NP1

Sl. No.

Irradiation Time (min)


1. 5 21.45

2. 10 36.25

3. 15 50.41

4. 20 63.83

5. 25 72.85

6. 30 80.21

7. 35 81.32

8. 40 82.09

9. 45 82.69

10. 50 83.02

11. 55 83.08

12. 60 83.11

13. 90 83.15

14. 120 83.17

118

0 20 40 60 80 100 120

20

40

60

80

Per

cent

age

dye

rem

oval

Irradiation time (min) Figure 5.5 Effect of irradiation time on the photocatalytic removal of MO by NP1


The photocatalytic removal of the MO by NP2 was carried out by

varying the dosage of the photocatalyst and the irradiation time.


MO by NP2





dosage, the dye removal was almost negligible.



Sl. No.



1. 0.2 30.59

119

2. 0.4 43.56

3. 0.6 54.93

4. 0.8 63.99

5. 1 71.95

6. 1.2 80.02

7. 1.4 85.19

8. 1.6 85.39

9. 1.8 85.46

10. 2 85.50

0.0 0.5 1.0 1.5 2.0

30

40

50

60

70

80

90

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL -1)

Figure 5.6 Effect of dosage of the photocatalyst on the

photocatalytic removal of MO by NP2

5.9.2 Effect of irradiation time on the photocatalytic removal of MO

by NP2

The effect of irradiation time was studied by keeping the amount of

photocatalyst fixed (optimum dosage) and varying the irradiation time

from 5 minutes to 120 minutes as described in Section 5.6.2. From

Table 5.4 and Figure 5.7 the optimum irradiation time was found to be

120

45 minutes for which the percentage dye removal was 87.41. Beyond

45 minutes, the dye removal was almost negligible.


of MO by NP2

Sl. No.



1. 5 28.95

2. 10 41.33

3. 15 55.92

4. 20 68.92

5. 25 79.13

6. 30 85.19

7. 35 85.99

8. 40 86.69

9. 45 87.41

10. 50 87.50

11. 55 87.55

12. 60 87.58

13. 90 87.60

14. 120 87.61

0 20 40 60 80 100 12020

40

60

80

Per

cent

age

dye

rem

oval

Irradaiation time (min)

121

Figure 5.7 Effect of irradiation time on the photocatalytic



The removal of the dye methyl orange by NP3 was also studied by

varying the dosage of the photocatalyst and the irradiation time.

5.10.1 Effect of dosage of the photocatalyst on the photocatalytic


The effect of dosage was studied by varying the amount of

photocatalyst from 0.2 to 2 g per liter of the dye solution. As is evident

from Table 5.5 and Figure 5.8, the maximum dosage was found to be

1.4 gL-1 corresponding to a dye removal of around 90.68%. Beyond this

optimum dosage, negligible removal of the dye occurred.

Table 5.5 Effect of dosage of photocatalyst on the photocatalytic

removal of MO by NP3.

Sl. No.



1. 0.2 35.92

2. 0.4 50.25

3. 0.6 62.19

4. 0.8 74.92

5. 1.0 84.56

6. 1.2 90.37

7. 1.4 90.68

8. 1.6 90.79

9. 1.8 90.81

10. 2.0 90.82

122

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.230

40

50

60

70

80

90

100

Per

cent

age

dye

rem

oval


Figure 5.8 Effect of dosage of photocatalyst on the

photocatalytic removal of MO by NP3


of MO by NP3

In order to study the effect irradiation time, the amount of

photocatalyst was fixed (optimum dosage) and the irradiation time was

varied from 5 minutes to 120 minutes (Section 5.6.2). Table 5.6 and

Figure 5.9 show the results for the same. The optimum irradiation time

was found to be 40 minutes for which the percentage dye removal was

93.92%. Beyond 40 minutes, the removal OF MO was negligible.

123


of MO by NP3

Sl. No.



1. 5 30.92 2. 10 47.53 3. 15 62.25 4. 20 75.39 5. 25 84.9 6. 30 90.37 7. 35 92.45 8. 40 93.92 9. 45 94.10 10. 50 94.17 11. 55 94.22 12. 60 94.25 13. 90 94.27 14. 120 94.28

0 20 40 60 80 100 120

40

60

80

100

Per

cent

age

dye

rem

oval

Irradiation time (min) Figure 5.9 Effect of irradiation time on the photocatalytic


5.11 Photocatalytic removal of rhodamine B dye

Rhodamine B is a chemical compound and a dye. It is usually

used as a tracer dye within water in order to determine the rate and

124

direction of flow and transport. It exhibits fluorescence and hence can

be detected easily and inexpensively with instruments called as

fluorometers. Rhodamine B is extensively used in biotechnology

applications such as flow cytometry, fluorescence

microscopy, fluorescence correlation spectroscopy etc. In biology, it is

used as a staining fluorescent dye.

The structure of rhodamine B is shown in Figure 5.10. It is a

cationic dye with molecular formula C28H31ClN2O3 and molecular mass

479.02 gmol-1. The chemical name of RhB is [9-(2-carboxyphenyl)-6-

diethylamino-3-xanthenylidene]-diethylammonium chloride. Figure 5.11

shows the absorbance spectrum of rhodamine B. The dye shows

maximum absorbance at 556 nm.

Figure 5.10 Structure of rhodamine B dye

125

200 300 400 500 600 700 800 900

0.0

0.5

1.0

1.5

2.0

Abs

orba

nce

W avelength (nm) Figure 5.11 Absorbance spectrum of rhodamine B dye

5.11.1Preparation of the dye solution

The concentration of rhodamine B dye used in all the

photodegradation experiments was 20 ppm. 1 g of the dyestuff was







The removal of RhB by NP1 was studied by varying the dosage

of the photocatalyst and the irradiation time.


RhB by NP1

The effect of dosage was studied by varying the amount of NP1

from 0.2 to 2.2 g per litre of the dye solution. From Table 5.7 and Figure

5.12 the optimum dosage was found to be 1.8 gL-1. The dye removal at

126

this optimum dosage was 77.45%. Beyond the optimum dosage, the

removal of the dye was almost negligible.


removal of RhB by NP1.

Sl. No.



1. 0.2 26.03

2. 0.4 38.45

3. 0.6 48.05

4. 0.8 54.32

5. 1.0 63.23

6. 1.2 69.15

7. 1.4 73.25

8. 1.6 75.56

9. 1.8 77.45

10. 2.0 77.56

11. 2.2 77.6

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

Per

cent

age

dye

rem

oval



photocatalytic removal of RhB by NP1

127


of RhB by NP1






79.93. Beyond 50 minutes, the dye removal was found to be negligible.

Table 5.8 Effect of irradiation time on the photocatalytic removal of RhB

by NP1.

Sl. No.



1. 5 21.09

2. 10 34.12

3. 15 47.13

4. 20 60.15

5. 25 70.80

6. 30 76.45

7. 35 78.35

8. 40 78.93

9. 45 79.45

10. 50 79.93

11. 55 79.99

12. 60 80.05

13. 90 80.07

14. 120 80.09

128

0 20 40 60 80 100 120

20

40

60

80

Per

cent

age

dye

rem

oval

Irradiation time (min)

Figure 5.13 Effect of irradiation time on the photocatalytic removal of RhB dye by NP1

5.13 Photocatalytic removal of Rhodamine B dye by NP2

The removal of RhB by NP2 was studied by varying the dosage of



RhB by NP2





dosage, the degradation was negligible.

129



Sl. No.



1. 0.2 28.49

2. 0.4 40.42

3. 0.6 50.73

4. 0.8 59.92

5. 1.0 68.00

6. 1.2 74.05

7. 1.4 78.02

8. 1.6 81.34

9. 1.8 81.42

10. 2.0 81.45

11. 2.2 81.47

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL -1) Figure 5.14 Effect of dosage of photocatalyst on the


130


of RhB by NP2






83.45. Beyond the optimum irradiation time, the dye removal was

almost negligible.

Table 5.10 Effect of irradiation time on the photocatalytic removal of RhB by NP2

Sl. No.



1. 5 24.83

2. 10 38.15

3. 15 51.89

4. 20 63.85

5. 25 72.85

6. 30 81.34

7. 35 82.54

8. 40 82.99

9. 45 83.45

10. 50 83.50

11. 55 83.54

12. 60 83.58

13. 90 83.6

14. 120 83.61

131

0 20 40 60 80 100 120

20

40

60

80

Per

cent

age

dye

rem

oval



removal of RhB dye by NP2

5.14 Photocatalytic removal of Rhodamine B dye by NP3

The removal of RhB by NP3 was studied by varying the dosage



RhB by NP3




dye removal at this optimum dosage was 84.92%. Beyond this optimum

dosage, the dye removal was almost negligible.

132



Sl. No.



1. 0.2 31.21

2. 0.4 44.92

3. 0.6 55.63

4. 0.8 64.11

5. 1.0 72.15

6. 1.2 79.56

7. 1.4 84.92

8. 1.6 85.01

9. 1.8 85.04

10. 2.0 85.06

11. 2.2 85.07

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

90

Per

cent

age

dye

rem

oval



133


of RhB by NP3






85.67. Beyond 35 minutes, there was negligible removal of the dye.

Table 5.12 Effect of irradiation time on the photocatalytic removal of RhB by NP3

Sl. No.



1. 5 27.82

2. 10 40.50

3. 15 54.26

4. 20 67.51

5. 25 79.63

6. 30 84.92

7. 35 85.67

8. 40 85.71

9. 45 85.75

10. 50 85.78

11. 55 85.80

12. 60 85.82

13. 90 85.83

14. 120 85.84

134

0 20 40 60 80 100 12020

40

60

80

100

Per

cent

age

dye

rem

oval

Irradiation time (min) Figure 5.17 Effect of irradiation time on the photocatalytic removal

of RhB dye by NP3

5.15 Photocatalytic removal of methylene blue dye

Methylene blue is a heterocyclic aromatic dye with the molecular

formula C16H18N3SCl and molecular mass 319.85 gmol-1. It finds

applications in different fields such as biology and chemistry. At room

temperature it appears as a solid, odorless, dark green powder which

gives a blue solution when dissolved in water. It is a potent cationic dye

and is widely used as a redox indicator in analytical chemistry. Solutions

of this substance are blue in an oxidizing environment, but turn

colorless when exposed to a reducing agent.

MB is added to bone cement in orthopaedic operations to provide

easy discrimination between native bone and cement. It accelerates the

hardening of bone cement thus increasing the speed at which bone

cement can be effectively applied. The cardiovascular effects of

methylene blue include hypertension and precordial pain. It also causes

135

dizziness, mental confusion head ache, fever, faecal and urine

discolouration, nausea, vomiting, abdominal pain and anemia.

The structure of methylene blue is shown in Figure 5.19.

Chemically, it is 3,7-bis(dimethylamino)-phenothiazin-5-ium chloride.

Figure 5.20 shows the absorbance spectrum of methyl orange. The dye

shows maximum absorbance at 665 nm.

.

Figure 5.18 Structure of methylene blue dye

200 300 400 500 600 700 800 900

0.0

0.5

1.0

1.5

2.0

Abs

orba

nce

Wavelength (nm)

Figure 5.19 Absorbance spectrum of methylene blue dye

136

5.15.1 Preparation of the dye solution

The concentration of methylene blue dye used in all the

photocatalytic experiments was 20 ppm. 1 g of the dye stuff was







The removal of MB by NP1 was studied by varying the dosage of



MB by NP1





dosage, the dye removal was found to be negligible.

137


removal of MB by NP1.

Sl. No.



1. 0.2 24.39

2. 0.4 36.89

3. 0.6 47.14

4. 0.8 56.83

5. 1.0 63.25

6. 1.2 67.92

7. 1.4 71.83

8. 1.6 73.99

9. 1.8 74.05

10. 2.0 74.08

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.220

30

40

50

60

70

80

Per

cent

age

dye

rem

oval



photocatalytic removal of MB dye by NP1

138


of MB by NP1






78.59. Beyond the optimum irradiation time, there was negligible

removal of MB.


of MB by NP1

Sl. No.



1. 5 18.23

2. 10 32.15

3. 15 43.82

4. 20 55.2

5. 25 65.82

6. 30 77.69

7. 35 78.25

8. 40 78.59

9. 45 78.64

10. 50 78.67

11. 55 78.70

12. 60 78.72

13. 90 78.73

14. 120 78.74

139

0 20 40 60 80 100 120

20

40

60

80

Per

cent

age

dye

rem

oval


Figure 5.21 Effect of irradiation time on the photocatalytic removal of MB by NP1





MB by NP2






140


removal of MB by NP2

Sl. No.



1. 0.2 28.39

2. 0.4 40.52

3. 0.6 50.84

4. 0.8 59.83

5. 1.0 66.30

6. 1.2 73.53

7. 1.4 77.69

8. 1.6 77.83

9. 1.8 77.89

10. 2.0 77.91

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL -1) Figure 5.22 Effect of dosage photocatalyst on the photocatalytic removal of MB by NP2 5.17.2 Effect of irradiation time on the photocatalytic removal

of MB by NP2




141



83.30. Beyond 40 minutes, the removal of MB was almost negligible.

Table 5.16 Effect of irradiation time on the photocatalytic removal of MB

by NP2

Sl. No.



1. 5 20.11

2. 10 35.52

3. 15 48.53

4. 20 60.03

5. 25 70.25

6. 30 81.15

7. 35 82.65

8. 40 83.30

9. 45 83.35

10. 50 83.40

11. 55 83.43

12. 60 83.46

13. 90 83.48

14. 120 83.49

0 20 40 60 80 100 120

20

40

60

80

Per

cent

age

dye

rem

oval



142





MB by NP3





dosage, the removal of MB was negligible.



Sl. No.



1. 0.2 27.95

2. 0.4 40.25

3. 0.6 50.12

4. 0.8 59.33

5. 1.0 67.04

6. 1.2 75.83

7. 1.4 81.15

8. 1.6 81.30

9. 1.8 81.35

10. 2.0 81.38

143

0.0 0.5 1.0 1.5 2.020

30

40

50

60

70

80

90

Per

cent

age

dye

rem

oval


photocatalytic removal of MB by NP3


of MB by NP3



varied from 5 minutes to 120 minutes as described in Section 5.6.2.

Table 5.18 and Figure 5.25 show the results for the same. The optimum

irradiation time was found to be 40 minutes for which the percentage

dye removal was 90.15. Beyond 40 minutes, there was negligible

removal of the dye.

144


of MB by NP3

Sl. No.



1. 5 25.30

2. 10 39.10

3. 15 54.85

4. 20 68.39

5. 25 80.56

6. 30 88.92

7. 35 90.15

8. 40 90.20

9. 45 90.26

10. 50 90.30

11. 55 90.32

12. 60 90.33

13. 90 90.34

14. 120 90.34

0 20 40 60 80 100 12020

40

60

80

100

Per

cent

age

dye

rem

oval




145

5.19 Regeneration of the photocatalysts

The possibility of reusing the three photocatalysts was examined

to determine the cost effectiveness of the method. Successive tests of

the photocatalytic degradation of the three dyes were performed. The

regeneration of all the three photocatalysts was done by soaking the

used photocatalyst in 0.1N NaOH solution.

10 mL of 0.1N NaOH solution was taken in a 250 mL Erlenmeyer

flask and about 100 mg of the used photocatalyst was added to it. The

mixture was then stirred magnetically at around 150 rpm at 250C for

about 1 hour. It was then filtered using the Whatman filter paper. The

residue collected in the filter paper was air-dried and then calcined for

about 2 hours at 450º C. It was then cooled to room temperature in a

desiccator. The regenerated photocatalysts were designated as in

Table 5.19.

Table 5.19 Codes of the photocatalysts before and after regeneration.

Sl. No.

Original Photocatalyst Code

Code after Regeneration

1. NP1 RNP1

2. NP2 RNP2

3. NP3 RNP3

The regenerated nanopowders RNP1, RNP2 and RNP3 were

also used to study the photocatalytic degradation of MO, RhB and MB

as in the case of the original photocatalysts.

146


The removal of MO by RNP1 was studied by varying the dosage



MO by RNP1




dye removal at this optimum dosage was found to be 58.74%. Beyond

the optimum dosage, the degradation of MO was negligible.


removal of MO by RNP1.

Sl. No.



1. 0.2 19.99

2. 0.4 28.84

3. 0.6 36.44

4. 0.8 42.96

5. 1.0 48.85

6. 1.2 53.28

7. 1.4 56.61

8. 1.6 58.55

9. 1.8 58.74

10. 2.0 58.77

147

0.0 0.5 1.0 1.5 2.0

20

30

40

50

60

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL-1)


photocatalytic removal MO by RNP1


of MO by RNP1

The effect of irradiation time was studied by keeping the amount

of photocatalyst fixed (optimum dosage) and varying the irradiation time


Table 5.21 and Figure 5.27 the optimum irradiation time was found to

be 50 minutes. The percentage dye removal at the optimum irradiation

time was found to be 60.60. Beyond 50 minutes, the removal of MO

was almost negligible.

148


of MO by RNP1.

Sl. No.



1. 5 15.65

2. 10 26.46

3. 15 36.79

4. 20 46.59

5. 25 53.17

6. 30 58.74

7. 35 59.35

8. 40 59.92

9. 45 60.35

10. 50 60.60

11. 55 60.64

12. 60 60.66

13. 90 60.69

14. 120 60.70

0 20 40 60 80 100 12010

20

30

40

50

60

Per

cent

age

dye

rem

oval



removal of MO by RNP1

149





MO by RNP2





dosage, there was negligible removal of MO.



Sl. No.



1. 0.2 23.24

2. 0.4 33.10

3. 0.6 41.74

4. 0.8 48.63

5. 1.0 54.68

6. 1.2 60.81

7. 1.4 64.74

8. 1.6 64.89

9. 1.8 64.94

10. 2.0 64.98

150

0.0 0.5 1.0 1.5 2.0

20

30

40

50

60

70

Per

cent

age

dye

rem

oval

Amount of nanopowder (gL-1) Figure 5.28 Effect of dosage of photocatalyst on the

photocatalytic removal of MO by RNP2


of MO by RNP2






time was found to be 66.36. Beyond 45 minutes, the dye removal was

negligible.

151

Table 5.23 Effect of irradiation time on the photocatalytic removal of MO

by RNP2

Sl. No.



1. 5 22.00

2. 10 31.41

3. 15 42.49

4. 20 52.37

5. 25 60.13

6. 30 64.74

7. 35 65.35

8. 40 65.88

9. 45 66.36

10. 50 66.42

11. 55 66.48

12. 60 66.51

13. 90 66.53

14. 120 66.54

0 20 40 60 80 100 120

20

30

40

50

60

70

Per

cent

age

dye

rem

oval



152



of the photocatalyst and the irradiation time


MO by RNP3





dosage, the dye removal was found to be negligible.



Sl. No.



1. 0.2 28.73

2. 0.4 40.20

3. 0.6 49.75

4. 0.8 59.93

5. 1.0 67.64

6. 1.2 72.49

7. 1.4 72.54

8. 1.6 72.63

9. 1.8 72.64

10. 2.0 72.65

153

0.0 0.5 1.0 1.5 2.0

30

40

50

60

70

80

Per

cent

age

dye

rem

oval




of MO by RNP3






time was found to be 75.40. Beyond 45 minutes, the dye removal was

negligible.

154

Table 5.25 Effect of irradiation time on the photocatalytic removal of

MO by RNP3

Sl. No.



1. 5 24.73

2. 10 38.02

3. 15 49.80

4. 20 60.31

5. 25 67.92

6. 30 72.49

7. 35 73.96

8. 40 75.01

9. 45 75.40

10. 50 75.44

11. 55 75.46

12. 60 75.50

13. 90 75.52

14. 120 75.53

0 20 40 60 80 100 12020

30

40

50

60

70

80

Per

cent

age

dye

rem

oval



155


The removal of RhB by RNP1 was studied by varying the dosage



RhB by RNP1


photocatalyst from 0.2 to 2.2g per litre of the dye solution. From Table





removal of RhB by RNP1.

Sl. No.



1. 0.2 19.00

2. 0.4 28.06

3. 0.6 35.07

4. 0.8 39.65

5. 1.0 46.15

6. 1.2 50.47

7. 1.4 53.47

8. 1.6 55.15

9. 1.8 56.53

10. 2.0 56.61

11. 2.2 56.64

156

0.0 0.5 1.0 1.5 2.0 2.5

20

30

40

50

60

Per

cent

age

dye

rem

oval


Figure 5.32 Effect of dosage photocatalyst on the photocatalytic



of RhB by RNP1







157

Table 5.27 Effect of irradiation time on the photocatalytic removal of

RhB by RNP1

Sl. No.



1. 5 15.59

2. 10 25.23

3. 15 34.85

4. 20 44.48

5. 25 52.36

6. 30 56.53

7. 35 57.94

8. 40 58.37

9. 45 58.95

10. 50 59.06

11. 55 59.10

12. 60 59.14

13. 90 59.16

14. 120 59.18

0 20 40 60 80 100 12010

20

30

40

50

60

Per

cent

age

dye

rem

oval




158

5.24 Photocatalytic removal of Rhodamine B dye by RNP2

The removal of RhB by RNP2 was studied by varying the dosage



RhB by RNP2



5.28 and Figure 5.34 the optimum dosage was found to be 1.6 gL-1 for

which the dye removal was 61.81%. Beyond the optimum dosage, the

dye removal was found to be negligible.



Sl. No.



1. 0.2 21.65

2. 0.4 30.71

3. 0.6 38.55

4. 0.8 45.53

5. 1.0 51.68

6. 1.2 56.27

7. 1.4 59.29

8. 1.6 61.81

9. 1.8 61.87

10. 2.0 61.90

11. 2.2 61.91

159

0.0 0.5 1.0 1.5 2.0 2.5

20

30

40

50

60

70

Per

cent

age

dye

rem

oval

Amount of nanopowder(gL-1)


photocatalytic removal of RhB by RNP2


of RhB by RNP2



varied from 5 minutes to 120 minutes as described in Section 5.6.2.

Table 5.29 and Figure 5.35 show the results for the same. The optimum

irradiation time was found to be 45 minutes for which the percentage

dye removal was 63.42. Beyond 45 minutes, the removal of RhB was

found to be negligible.

160


of RhB by RNP2

Sl. No.



1. 5 18.87

2. 10 28.99

3. 15 39.43

4. 20 48.52

5. 25 55.36

6. 30 61.81

7. 35 62.73

8. 40 63.07

9. 45 63.42

10. 50 63.46

11. 55 63.49

12. 60 63.52

13. 90 63.53

14. 120 63.54

0 20 40 60 80 100 120

20

30

40

50

60

70

Per

cent

age

dye

rem

oval


removal of RhB by RNP2

161

5.25 Photocatalytic removal of Rhodamine B dye by RNP3

The removal of RhB by RNP3 was studied by varying the dosage of



RhB by RNP3





dye degradation was negligible.



Sl. No.



1. 0.2 25.59

2. 0.4 36.83

3. 0.6 45.61

4. 0.8 52.57

5. 1.0 59.16

6. 1.2 65.23

7. 1.4 69.63

8. 1.6 69.70

9. 1.8 69.73

10. 2.0 69.74

11. 2.2 69.75

162

0.0 0.5 1.0 1.5 2.0 2.520

30

40

50

60

70

Per

cent

age

dye

rem

oval


removal of RhB by NP3


of RhB by RNP3







163


of RhB by RNP3

Sl. No.



1. 5 22.81

2. 10 33.21

3. 15 44.49

4. 20 55.35

5. 25 65.29

6. 30 69.63

7. 35 70.24

8. 40 70.29

9. 45 70.33

10. 50 70.36

11. 55 70.38

12. 60 70.40

13. 90 70.41

14. 120 70.42

0 20 40 60 80 100 120

20

30

40

50

60

70

Per

cent

age

dye

rem

oval


removal of RhB dye by NP3

164


The removal of MB by RNP1 was studied by varying the dosage



MB by RNP1





dye removal was negligible.


removal of MB by RNP1.

Sl. No.



1. 0.2 20.29

2. 0.4 28.97

3. 0.6 36.35

4. 0.8 42.77

5. 1.0 47.40

6. 1.2 52.57

7. 1.4 55.58

8. 1.6 55.64

9. 1.8 55.69

10. 2.0 55.70

165

0.0 0.5 1.0 1.5 2.0

20

30

40

50

60

Per

cent

age

dye

rem

oval



removal of MB by RNP1


of MB by RNP1







166


of MB by RNP1

Sl. No.



1. 5 12.52

2. 10 22.78

3. 15 31.76

4. 20 39.14

5. 25 46.78

6. 30 52.43

7. 35 53.04

8. 40 53.31

9. 45 53.77

10. 50 53.79

11. 55 53.82

12. 60 53.85

13. 90 53.87

14. 120 53.89

0 20 40 60 80 100 120

10

20

30

40

50

60

Per

cent

age

dye

rem

oval



167





MB by RNP2








Sl. No.



1. 0.2 21.43

2. 0.4 30.59

3. 0.6 38.38

4. 0.8 45.17

5. 1.0 50.05

6. 1.2 55.51

7. 1.4 58.69

8. 1.6 58.76

9. 1.8 58.80

10. 2.0 58.82

168

0.0 0.5 1.0 1.5 2.0

20

30

40

50

60

Per

cent

age

dye

rem

oval




of MB by RNP2







169


of MB by RNP2.

Sl. No.



1. 5 14.53

2. 10 25.67

3. 15 35.07

4. 20 43.38

5. 25 50.77

6. 30 58.65

7. 35 59.73

8. 40 60.20

9. 45 60.24

10. 50 60.28

11. 55 60.30

12. 60 60.32

13. 90 60.33

14. 120 60.34

0 20 40 60 80 100 12010

20

30

40

50

60

Per

cent

age

dye

rem

oval



170





MB by RNP3








Sl. No.



1. 0.2 22.08

2. 0.4 31.79

3. 0.6 39.59

4. 0.8 46.87

5. 1.0 52.96

6. 1.2 59.90

7. 1.4 64.10

8. 1.6 64.22

9. 1.8 64.26

10. 2.0 64.29

171

0.0 0.5 1.0 1.5 2.0

20

30

40

50

60

70

Per

cent

age

dye

rem

oval





of MB by RNP3







172


of MB by RNP3

Sl. No.



1. 5 21.27

2. 10 33.78

3. 15 47.72

4. 20 59.57

5. 25 70.50

6. 30 74.91

7. 35 77.02

8. 40 77.10

9. 45 77.16

10. 50 77.20

11. 55 77.24

12. 60 77.26

13. 90 77.28

14. 120 77.30

0 20 40 60 80 100 120

20

30

40

50

60

70

80

Per

cent

age

dye

rem

oval



173


The three nanopowders NP1, NP2 and NP3 were used for the

photocatalytic removal of three dyes; methyl orange, rhodamine B and

methylene blue under UV light irradiation. It was found that the

photocatalytic efficiency of the nanopowders in case of all the three

nanopowders followed the order:

NP3 > NP2 > NP1.

From a detailed study of the results obtained, it was concluded

that the nanopowders NP3 and NP2 exhibit better photocatalytic

efficiency than NP1 which might be attributed to the smaller crystallite

size and large BET surface area of NP3 and NP2 than those of NP1.

The effect of regeneration on the photocatalytic efficiency of the

three nanopowders was also studied. The efficiency of the regenerated

nanopowders followed the order:

RNP3 > RNP2 > RNP1.

The photocatalytic efficiency of the regenerated nanopowders

was found to be less than that of the original nanopowders. This is

because some of the active sites on the surface of the nanopowders are

blocked by the adsorption of the some of the organic compounds

formed during the photocatalytic degradation of the dye.

CHAPTER 6

REDUCTION IN COD OF AN INDUSTRIAL

EFFLUENT

174

6.1 Chemical oxygen demand

The chemical oxygen demand (COD) is a measure of the oxygen

equivalent of organic matter content of a sample that is susceptible to

oxidation by a strong chemical oxidant such as potassium dichromate.

For samples from a particular source, the COD can be related

empirically to biochemical oxygen demand, organic carbon or organic

matter. The wastewater generated from various types of industries is

highly polluting because it contains high biochemical oxygen demand

(BOD), chemical oxygen demand (COD), toxic substances, recalcitrant

organic compounds and colouring matter such as dyes and pigments

[154- 156]. The effluents originating from the Kraft process contain

lignin, carboxylic acids, phenolic compounds, sulfur compounds,

terpenes, resins and many more [157, 158]. The wood extractives from

the cooking operations have poor solubility and high toxicity and are

therefore not easily amenable to biological treatment. To make the

treatment cost effective as well as efficient in the removal of toxic

organic compounds and color, coagulation/flocculation can be used as

an effective primary treatment method. In this method, a maximum of

colloids and dissolved solids present in the wastewater can be removed

by hydrolyzing metal salts using different coagulants. The precipitation

of dissolved lignin and other matters using different coagulants such as

alum, ferric chloride, poly aluminium chloride (PAC) and lime have been

reported by several researchers [159, 160]. The industry generally uses

175

primary physicochemical treatment followed by secondary treatment

such as wet air oxidation, incineration or biological treatment [161, 162].

6.2 Study area – The Vrishbhavathi River

The Vrishabhavathi River is a minor river that flows through the

south of the Indian city of Bangalore, India. It is a tributary of

the Cauvery River. It was once a serene river flowing across many

localities of Bangalore. Bangalore south has more of an undulating

terrain with hills and valleys. The Vrishabhavathi River takes birth in one

of the small hills in this area. The river runs parallel to Mysore road for

several kilometers [163, 164]. It flows through areas like Guddadahalli,

Bapujinagar and Rajarajeshwari Nagar.

Till the 1970s, the VrishbhavathiRiver was a source of livelihood

for hundreds of people of Bangalore and was also a place for river

water swimming and lazing around. Later, due to the establishment of

several industries and business establishments on its banks, the river

lost its glory and pristine quality and turned into a drain. The

Vrishbhavathi River became a sewage river, tanks dried up; other water

bodies were breached and tank bunds and catchments areas were

encroached upon and construction activities were allowed. Naturally,

the water bodies became septic and the Vrishabhavathi River became

nothing more than a huge cesspool. Today, it is highly polluted due to

the pollutants from various industrial, agricultural and domestic sources.

The Vrishbhavathi River is a potential carrier of epidemics and villagers

176

downstream have complained of diseases and health hazards arising

out of acute pollution and filthy water. The residents of Byramangala,

Chowkalli and Gopalli areas have complained of several health related

diseases and studies by several scientific and academic institutions

have pinpointed the polluted Vrishbhavathi River as the reason.

The water of the wells and borewells around the course of the

river is also highly polluted. Studies conducted by several research

institutions have identified water from the lake as well as open and bore

wells in the area as non-potable, with high levels of fecal coliforms

making it unfit not only for human consumption, but also for use by

animals or for agriculture. The water of the polluted Vrishbhavathi River

is extensively used for irrigating farm lands across its both sides from

Kengeri to Byramangala tank which accounts for about forty five

kilometres away from the origin of the river.

Bangalore is located at a latitude of 12o.58’N, longitude of

77o.35’E and an altitude of 921 m above the mean sea level [165]. It

has three drainage watersheds viz., the Vrishbhavathi, Bellandur and

Nagavara watershed among which the Vrishbhavathi watershed is the

largest [166]. It carries polluted effluents from two major industrial areas

of Bangalore, viz., Peenya and Rajajinagar. The domestic sewage

effluents of both treated and untreated water are directly discharged in

to it from a large part of thecity. It also carries industrial effluents along

the Bangalore-Mysore state highway factories and the Bidadi Industrial

177

area. The Vrishbhavathi River drains an aerial extent of 545 sq. km

before it joins the Suvarnamukhi River at Bhadragundadoddi of

Kanakapura Taluk, Bangalore District. Plates 6.1 to 6.4 give an idea

about the present status of the Vrishbhavathi River.

Plate 6.1 The Vrishbhavathi River (Photo 1)

178




179

In this chapter, the reduction in the COD of the effluent water

collected from the Kengeri area of Bangalore using the three

nanopowders has been reported.

6.2.1 Sampling and analysis

The geological pattern and chemistry of water are highly affected

by the input of materials containing minerals, their solubility and the

chemical equilibrium prevailing in the aqueous solution. The major ions,

which are naturally available in surface and ground water, are variable

due to the local geological, climatic and geographical conditions [167,

168]. The minerals dissolved in water mainly include the carbonates,

sulfates and chlorides of calcium, magnesium and sodium along with

calcium bicarbonate and magnesium sulfate. These natural salts exist

in large quantities found in the water depending on the composition of

the ground over which the water flows.

In order to understand the quality of the river water, the sampling

of the river water was done in order to pursue the quality of the water

and for making forecasts and to determine the extent of damage due to

pollution [167]. For developing a sampling design, due attention was

paid to the sampling unit, source and size of the sample, parameters of

importance and sampling procedures.

The wastewater samples used in the present study were the final

treated effluent released from several industries into the Vrishbhavathi

180

River. The water samples were collected during January 2011 from the

Kengeri area of Bangalore, India through which the Vrishbhavathi River

flows. The samples were collected in five liter dry polythenebottles

which were earlier washed with double distilled water and dried. Later,

500 mL of the collected water samples were acidified with analytical

grade nitric acid to prevent the precipitation of metals. At the time of the

study, the effluent was filtered through Whatman filter paper No. 45 in

order to remove any suspended particulate matter.

6.2.2 Sample preservation

The effluent samples were 24 h composite samples, collected in

polythene bottles. All the samples were taken after the final treatment.

The samples were refrigerated at 4° C and prior to the study, they were

brought to room temperature (24 to 27° C).

6. 3 Open reflux method for the determination of COD

In the open reflux method, the sample is refluxed in strongly

acidic solution with a known excess of potassium dichromate [264].

After digestion, the remaining unreduced K2Cr2O7 is titrated with

standard ferrous ammonium sulphate solution to determine the amount

of K2Cr2O7 consumed and the oxidizable organic matter is calculated in

terms of oxygen equivalent. Ag2SO4is added as a catalyst to promote

oxidation of certain compounds such as straight chain aliphatic

compounds and acetic acid. The interference of halide ions, particularly

181

chloride is eliminated by the addition of HgSO4. The COD digester is

shown in Plate 6.5. It has the reflex apparatus consisting of 500 mL

capacity COD tubes with air condensers and a heating block which can

maintain temperature around 1800C.

Plate 6.5 The COD digester

6.3.1 Chemicals and reagents

All the chemicals were of analytical grade and were used without

further purification. Double distilled water was used throughout the

experiments.

6.3.2 Preparation of the reagents

1. Mercuric sulphate, HgSO4

2. Silver sulphate, Ag2SO4

3. Concentrated sulphuric acid

4. Standard potassium dichromate (0.25N)

182

K2Cr2O7 crystals were taken in a watch glass and dried in an oven

at 103oC for about 2 hours. 12.259g of the crystals were transferred

to a 1000 mL volumetric flask, dissolved in small quantity of double

distilled and then diluted upto the mark.

5. Standard ferrous ammonium sulfate solution (0.05N)

19.5 g of ferrous ammonium sulphate crystals were transferred to a

1000 mL volumetric flask, 10 mL of concentrated sulphuric acid was

added. After dissolving the crystals, the solution was diluted upto

the mark with double distilled water.

6. Ferroin indicator

1.485 g of analytical grade1, 10 phenanthroline monohydrate and

0.695 g of ferrous sulphate were dissolved in double distilled water

and the solution was diluted to 100 mL.

The FAS solution was standardized as follows. 5 mL of standard

K2Cr2O7 solution was pipetted out in a 250 mL conical flask and 15 mL

of concentrated sulphuric acid was added to it. The solution was

heated for 30 minutes and cooled to room temperature. 50 mL of

double distilled water was added to it and the reaction mixture was

then titrated against the standard FAS solution using 2 drops of ferroin

indicator till the blue green colour changed to reddish brown.

6.3.3 Determination of COD of the effluent sample without the

nanopowder

First the back titration was performed as follows.

183

1. The effluent sample was shaken well, so that the contents were

mixed thoroughly. It was then diluted 10 times with double

distilled water.

2. 10 mL of the diluted sample was transferred to the reflux tube.

Mercuric sulphate was added according to the chloride

concentration and mixed well to dissolve HgSO4.

3. A pinch of Ag2SO4 was added followed by the addition of 15 mL

of concentrated H2SO4 along the sides and cooled.

4. 5 mL of the standard K2Cr2O7 solution was then added and

mixed well.

5. The reflux tube was then placed in the COD digester and the

air condenser was attached to it. The open end of the

condenser was covered with a small beaker to prevent the

foreign material from entering the refluxing mixture. The mixture

was then refluxed at around 1800C for 2 hours.

6. After refluxing for 2 hours, the reflux tube was cooled to room

temperature. 40mL of double distilled water was added to it.

7. The reaction mixture was then titrated against the FAS solution

using 2 drops of ferroin indicator till the blue green colour

changed to reddish brown.

The blank titration was performed in the same manner except that

10 mL of double distilled water was used instead of the diluted sample.

184

The COD value was calculated from Equation 6.1 and expressed in

units of mg of oxygen per litre of the effluent sample.

….. (6.1)

where, A = Volume (mL) of FAS solution consumed in case of blank

titration,

B = Volume (mL) of FAS solution consumed in case of back titration,

N = Normality of FAS solution, and

V = Volume (mL) of the diluted effluent sample.

The value of COD of the effluent sample without the nanopowder was

considered as P.

6.3.4 Determination of COD of the effluent sample with the

nanopowder

First the back titration was performed as follows.

1. The effluent sample was shaken well, so that the contents

were mixed thoroughly. It was then diluted 10 times with

double distilled water.

2. 10 mL of the diluted sample was transferred to the reflux tube.

A known mass of the nanopowder was added to it. Mercuric

sulphate was added according to the chloride concentration

and mixed well to dissolve HgSO4.

3. A pinch of Ag2SO4 was added followed by the addition of 15 mL

of concentrated H2SO4 along the sides and cooled.

4. 5 mL of the standard K2Cr2O7 solution was then added and

185

mixed well.

5. The reflux tube was then placed in the COD digester and the

air condenser was attached to it. The open end of the

condenser was covered with a small beaker to prevent the

foreign material from entering the refluxing mixture. The mixture

was then refluxed at around 1800C for 2 hours.

6. After refluxing for 2 hours, the reflux tube was cooled to room

temperature. 40mL of double distilled water was added to it.

7. The reaction mixture was then titrated against the FAS solution

using 2 drops of ferroin indicator till the blue green colour

changed to reddish brown.

The blank titration was performed in the same manner except that

10 mL of double distilled water was used instead of the diluted sample.

The Blank Titration was performed in the same manner except that 10

ml of double distilled water was used instead of the diluted sample. The

COD value was calculated from Equation 6.1.

The value of COD of the effluent sample without the nanopowder

was considered as Q. The experiments were conducted using the batch

adsorption technique by varying the amount of the nanopowder. For

each dosage of the nanopowder the percentage COD reduction was

calculated using Equation 6.2.

….. (6.2)

where, P = COD of the effluent sample without the nanopowder and

186

Q = COD of the effluent sample with the nanopowder.

The optimum dosage of the nanopowder was thus determined.

The effect of contact time on the reduction in COD was

determined by using optimum dosage of the nanopowder. The batch

experiments for the removal of COD were conducted at different values

of the contact time. The contact time was varied from 5 minutes to 60

minutes with increments of 5 minutes. The reduction in COD for contact

time of 90 and 120 minutes was also calculated. In each case the

reduction in COD was calculated using Equation 6.2 and the optimum

contact time was determined.

The COD reduction experiments were performed using all the

three nanopowders individually and a comparison of the efficiency of

the three nanopowders in reducing the COD of the industrial effluent

was made.


The reduction in COD of the industrial effluent by NP1 was

studied by varying the dosage of the nanopowder and the contact time.

6.4.1 Effect of dosage of the nanopowder on the reduction in

COD of the industrial effluent by NP1


nanopowder from 0.1 to 1.4 g per litre of the industrial effluent. From

Table 6.1 and Figure 6.1 the optimum dosage was found to be 1.1 gL-1.

The reduction in COD at this optimum dosage was 74.78%. Beyond the

187

optimum dosage, the reduction in COD of the industrial effluent was


Table 6.1 Effect of dosage of the nanopowder on the reduction in COD

of the industrial effluent by NP1.

Sl. No.

Dosage of the Nanopowder (gL-1)

Percentage COD Reduction

1. 0.1 11.23

2. 0.2 25.25

3. 0.3 31.93

4. 0.4 43.85

5. 0.5 54.98

6. 0.6 66.65

7. 0.7 68.92

8. 0.8 70.25

9. 0.9 72.56

10. 1.0 73.93

11. 1.1 74.78

12. 1.2 74.85

13. 1.3 74.90

14. 1.4 74.92

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

20

40

60

80

Per

cent

age

CO

D r

educ

tion


Figure 6.1 Effect of dosage of the nanopowder on the reduction in


188

6.4.2 Effect of contact time on the reduction in COD of the

industrial effluent by NP1

In order to study the effect of contact time, the amount of

nanopowder was fixed (optimum dosage) and the contact time was

varied from 5 minutes to 60 minutes in increments of 5 minutes. The

effect of contact time for 90 and 120 minutes was also studied. Table

6.2 and Figure 6.2 show the results for the same. The optimum contact

time was found to be 50 minutes for which the percentage COD

reduction was found to be 82.75. Beyond the optimum contact time, the

reduction in the COD of the industrial effluent was found to be

negligible.

Table 6.2 Effect of contact time on the reduction in COD of the

industrial effluent by NP1.

Sl. No.

Contact Time (min)


1. 5 16.09

2. 10 28.72

3. 15 40.96

4. 20 52.84

5. 25 62.32

6. 30 74.78

7. 35 77.83

8. 40 80.89

9. 45 82.03

10. 50 82.75

11. 55 82.82

12. 60 82.90

13. 90 82.94

14. 120 82.96

189

0 20 40 60 80 100 12010

20

30

40

50

60

70

80

90

Per

cent

age

CO

D r

educ

tion

Contact time (min)

Figure 6.2 Effect of contact time on the reduction in COD of the










The reduction in COD at the optimum dosage was found to be 78.83%.

Beyond the optimum dosage, the reduction in COD of the industrial

effluent was found to be negligible.

190

Table 6.3 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP2.

Sl. No.



1. 0.1 12.83

2. 0.2 27.00

3. 0.3 38.90

4. 0.4 49.15

5. 0.5 57.85

6. 0.6 64.72

7. 0.7 70.83

8. 0.8 75.25

9. 0.9 78.83

10. 1.0 78.88

11. 1.1 78.91

12. 1.2 78.92

0.0 0.2 0.4 0.6 0.8 1.0 1.2

10

20

30

40

50

60

70

80

Per

cent

age

CO

D r

educ

tion


Figure 6.3 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP2

191










reduction in the COD of the industrial effluent was almost negligible.

Table 6.4 Effect of contact time on the reduction in COD of the industrial

effluent by NP2.

Sl. No.

Contact Time (min)


1. 5 17.39

2. 10 29.50

3. 15 41.99

4. 20 53.83

5. 25 64.92

6. 30 78.83

7. 35 80.56

8. 40 82.23

9. 45 83.81

10. 50 83.90

11. 55 83.96

12. 60 83.99

13. 90 84.02

14. 120 84.04

192

0 20 40 60 80 100 12010

20

30

40

50

60

70

80

90

Per

cent

age

CO

D r

educ

tion

Contact time (min)














193

Table 6.5 Effect of dosage of the nanopowder on the reduction in COD of the industrial effluent by NP3.

Sl. No.



1. 0.1 15.02

2. 0.2 29.05

3. 0.3 42.83

4. 0.4 54.15

5. 0.5 64.92

6. 0.6 73.63

7. 0.7 79.92

8. 0.8 84.15

9. 0.9 84.22

10. 1.0 84.26

11. 1.1 84.29

12. 1.2 84.31

0.0 0.2 0.4 0.6 0.8 1.0 1.2

10

20

30

40

50

60

70

80

90

Per

cent

age

CO

D r

educ

tion








194






reduction in the COD of the industrial effluent was found to be

negligible.


industrial effluent by NP3.

Sl. No.

Contact Time (min)


1. 5 23.65

2. 10 41.93

3. 15 58.59

4. 20 70.03

5. 25 79.25

6. 30 84.15

7. 35 85.78

8. 40 85.80

9. 45 85.84

10. 50 85.87

11. 55 85.87

12. 60 85.88

13. 90 85.88

14. 120 85.88

195

0 20 40 60 80 100 120

20

30

40

50

60

70

80

90

Per

cent

age

CO

D r

educ

tion

Contact time (min)



6.7 Regeneration of the nanopowders

The removal of organic substances and other species adsorbed

onto the used nanopowders was done by soaking the nanopowder in

0.1N NaOH solution. 10 mL of 0.1N NaOH solution was taken in a 250

mL Erlenmeyer flask and about 100mg of the used nanopowder was

added to it. The mixture was then stirred magnetically at around 150

rpm at 250C for about 1 hour. The mixture was then filtered using the

Whatman filter paper. The residue collected in the filter paper was air-

dried and then calcined for about 2 hours at 450ºC. The regenerated

nanopowders were also used for the reduction in COD of the effluent

sample.

The codes used for the regenerated nanopowdersare shown in Table

6.7.

196

Table 6.7 Codes of the nanopowders before and after regeneration.

Sl. No.

Original Nanopowder Code

Code after Regeneration

1. NP1 RNP1

2. NP2 RNP2

3. NP3 RNP3

The regenerated nanopowders NP1, NP2 and NP3 were also

used to study the reduction in COD of the same industrial effluent

collected from the Vrishbhavathi River.

6.8 Reduction in COD of the industrial effluent by RNP1 The reduction in COD of the industrial effluent by RNP1 was



COD of the industrial effluent by RNP1







197


of the industrial effluent by RNP1.

Sl. No.



1. 0.1 7.91 2. 0.2 17.80 3. 0.3 22.51 4. 0.4 30.91 5. 0.5 38.76 6. 0.6 46.98 7. 0.7 48.58 8. 0.8 49.52 9. 0.9 51.15 10. 1.0 52.12 11. 1.1 52.71 12. 1.2 52.76 13. 1.3 52.80 14. 1.4 52.81

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.60

10

20

30

40

50

60

Per

cent

age

CO

D r

educ

tion





industrial effluent by RNP1



198






reduction in the COD was found to be negligible.


industrial effluent by RNP1.

Sl. No.

Contact Time (min)


1. 5 11.32

2. 10 20.21

3. 15 28.83

4. 20 37.19

5. 25 43.87

6. 30 52.71

7. 35 54.79

8. 40 56.94

9. 45 57.74

10. 50 58.39

11. 55 58.43

12. 60 58.46

13. 90 58.48

14. 120 58.50

199

0 20 40 60 80 100 120

10

20

30

40

50

60

Per

cent

age

CO

D r

educ

tion

Contact Time (min)

Figure 6.8 Effect of contact time on reduction in COD of the








Table 6.10 and Figure 6.9 the optimum dosage was found to be 0.9 gL-

1. The reduction in COD at the optimum dosage was found to be

56.75%. Beyond the optimum dosage, the reduction in COD of the

industrial effluent was found to be negligible.

200



Sl. No.



1. 0.1 9.23

2. 0.2 19.44

3. 0.3 28.00

4. 0.4 35.38

5. 0.5 41.65

6. 0.6 46.59

7. 0.7 50.99

8. 0.8 54.18

9. 0.9 56.75

10. 1.0 56.79

11. 1.1 56.81

12. 1.2 56.82

0.0 0.2 0.4 0.6 0.8 1.0 1.2

10

20

30

40

50

60

Per

cent

age

CO

D r

educ

tion




201






effect of contact time for 90 and 120 minutes was also studied (Section

6.3.3). Table 6.11 and Figure 6.10 show the results for the same. The

optimum contact time was found to be 45 minutes for which the

percentage COD reduction was found to be 59.54. Beyond the optimum

contact time, the reduction in the COD of the industrial effluent was




Sl. No.

Contact Time (min)


1. 5 12.52

2. 10 21.24

3. 15 30.23

4. 20 38.75

5. 25 46.74

6. 30 56.75

7. 35 58.00

8. 40 58.98

9. 45 59.54

10. 50 59.58

11. 55 59.60

12. 60 59.62

13. 90 59.63

14. 120 59.64

202

0 20 40 60 80 100 120

10

20

30

40

50

60

Per

cent

age

CO

D r

educ

tion

Contact time (min)

Figure 6.10 Effect of contact time on reduction in COD of the








Table 6.12 and Figure 6.11 the optimum dosage was found to be 0.8

gL-1. The reduction in COD at the optimum dosage was found to be

60.86%. Beyond the optimum dosage, the reduction in COD of the

industrial effluent was found to be negligible.

203



Sl. No.



1. 0.1 11.26 2. 0.2 21.78 3. 0.3 32.12 4. 0.4 40.61 5. 0.5 48.69 6. 0.6 54.62 7. 0.7 58.44 8. 0.8 60.86 9. 0.9 60.90 10. 1.0 60.92 11. 1.1 60.93 12. 1.2 60.93

0.0 0.2 0.4 0.6 0.8 1.0 1.2

10

20

30

40

50

60

Per

cent

age

CO

D r

educ

tion




204







6.13 and Figure 6.12 show the results for the same. The optimum

contact time was found to be 45 minutes for which the percentage COD

reduction was found to be 62.92. Beyond 45 minutes, the reduction in

the COD was almost negligible.



Sl. No.

Contact Time (min)


1. 5 15.48

2. 10 26.94

3. 15 36.44

4. 20 45.02

5. 25 52.68

6. 30 60.86

7. 35 62.08

8. 40 61.76

9. 45 62.92

10. 50 62.96

11. 55 62.99

12. 60 63.01

13. 90 63.03

14. 120 63.03

205

0 20 40 60 80 100 12010

20

30

40

50

60

70

Per

cent

age

CO

D r

educ

tion

Contact time (min)




The three nanopowders NP1, NP2 and NP3 were used for the

reduction in COD of the industrial effluent collected from the

Vrishbhavathi River of Bangalore, India. It was found that the efficiency

of the nanopowders in the reduction in COD of the industrial effluent

followed the order: NP3 > NP2 > NP1.

From the results obtained, it was concluded that the efficiency of

nanopowders NP3 and NP2 in the reduction in COD was better than

that of NP1. This can also be attributed to the smaller values of mean

crystallite size and large BET surface area of NP3 and NP2 than those

of NP1.

The effect of regeneration on the reduction in COD was also

studied. The efficiency of the regenerated nanopowders followed the

order: RNP3 > RNP2 > RNP1.

206

The efficiency of the regenerated nanopowders in the reduction in

COD was found to be less than that of the original nanopowders. This is

because some of the active sites on the surface of the nanopowders are

blocked by the adsorption of the some of the organic compounds

present in the industrial effluent.

CHAPTER 7

CONCLUSIONS

207

CONCLUSIONS

Three nanopowders NP1, NP2 and NP3 were successfully

synthesized by solution combustion method. The nanopowders were

characterized by PXRD, FTIR, SEM, UV-Visible Spectroscopy, Band

gap measurements and BET surface area measurements.

The three nanopowders were used as photocatalysts for the

degradation of three dyes methyl orange, rhodamine B and methylene

blue from their aqueous solutions.

The nanopowders were also used in the reduction in COD of the

industrial effluent from the Vrushbhavathi River of Bangalore, India.

The following conclusions can be drawn from the work:

1. The three metal oxide nanopowders NP1, NP2 and NP3 can be

easily synthesized by solution combustion method in a short period

of time.

2. The metal oxides synthesized by this method possess high

degree of purity as indicated by the PXRD patterns.

3. The three nanopowders exhibit photocatalytic activity in the order:

NP3 > NP2 > NP1 This can be attributed to their size and BET

surface area. The mean crystallite size followed the order: NP1 >

NP2 > NP3. The BET surface area followed the order: NP3 > NP2 >

NP1 The smaller value of mean crystallite size and high BET surface

area make NP3 a better photocatalyst than NP2 and NP1. NP1

208

exhibited least photocatalytic activity due to comparatively larger

value of mean crystallite size and lower BET surface area.

4. NP3 and NP2 can thus be efficiently used in the removal of dyes

from textile and paper mills.

5. The efficiency of the three metal oxides in the reduction of COD of

the industrial effluent from the Vrishbhavathi River of Bangalore

followed the order: NP3 > NP2 > NP1

Thus, apart from dye removal, the metal oxides can also be used

in the reduction in COD of industrial effluents.

6. The comparison of efficiencies of NP2 and NP1 in both dye

removal and reduction in COD of the industrial effluent,

indicates that α-Fe2O3synthesized using Glycine as fuel (NP2) is

a better hotocatalyst than α-Fe2O3 synthesized using ODH as fuel

(NP1). Thus Glycine is a better fuel than ODH in the

preparation of α-Fe2O3.

CHAPTER 8

REFERENCES

209

REFERENCES

1. M.N. Rao, A.K. Datta, Waste water treatment, Second Edition,

Oxford and IBH Publishing Co. Pvt. Ltd. (1978).

2. M. Ratner, D. Ratner, Nanotechnology: A Gentle Introduction to the

next big idea, Pearson Education, Inc., (2003).

3. A. Eychmuller, Structure and photophysics of semiconductor

nanocrystals, J. Phys. Chem. B, 104 (2000) 6514-6528.

4. C. N. R. Rao, A. Mueller, A. K. Cheetham, The Chemistry of

nano-materials: Synthesis, Properties and Applications, Vol. 1

Wiley-VCH,Weinheim (2004).

5. K.C. Patil, M.S. Hegde, Tanu Rattan, S.T. Aruna, Chemistry of

nanocrystalline oxide materials: Combustion synthesis, properties

and applications, World Scientific Publishing Co. Pvt. Ltd.(2008)

6. http://www.scitopics.com/Nano_Catalysis.html.

7. Saeedeh Hashemian, MnFe2O4/bentonite nano composite as a

novel magnetic material for adsorption of acid red 138, J. Biotech.,

9 (50) (2010) 8667 – 8671.

8. V.K. Garg, Removal of a basic dye from aqueous solution by

adsorption using timber industry waste, Biochem. Eng., 19 (1)

(2005) 75-80.

9. O. P. Panwar, Anil Kumar, Rameshwar Ameta, Suresh C. Ameta,

Use of zirconium phosphate system as a photocatalyst:

210

photobleaching of tolonium chloride, Macedonian Journal of

Chemistry and Chemical Engineering, 27 (2) (2008) 133–139.

10. Ashish Bansal, Deependar Sharma, Rakshit Ameta, Hari S.

Sharma, Photodegradation of rhodamine 6G in presence of

semiconducting ammonium phosphomolybdate, Int. J. Chem. Sci.,

8(4), 2010, 2747-2755.

11. S. Chinwetkitvanich, M. Tuntoolvest, T. Panswad, Anaerobic

decolorization of reactive dye bath effluents by two stage UASB

system with Tapioca as a co-substrate, Water Res., 34 (2000)

2223–2232.

12. C.L. Hsueh, Y.H. Huang, C.C.Wang, C.Y. Chen, Degradation of

azo dyes using low Fe concentration of Fenton and Fenton like

system, Chemosphere, 58 (2005) 1409-1414.

13. Z. Barhon, N. Saffaj, A. Albizane, M. Azzi, R. Mamouni, M. El

Haddad, Effect of modification of zirconium phosphate by silver on

photodegradation of methylene blue, J. Mater. Environ. Sci., 3 (5)

(2012) 879-884.

14. N. Saffaj, M. Persin, S.A. Younssi, A. Albizane, M. Bouhria, H.

Loukili, H. Dach, A. Larbot, Separation and Purification

Technology, 47 (2005) 36-42.

15. F. Harrelkas, A. Azizi, A. Yaacoubi, A. Benhammou, M. N. Pons,

Treatment of textile dye effluents using coagulation- flocculation

211

coupled with membrane processes or adsorption on powdered

activated carbon, Desalination, 235 (2009) 330-339.

16. S. Devipriya, S. Yesodharan, Photocatalytic degradation of

pesticide contaminants in water, Sol. Energy Mater. Sol. Cells, 86

(2005) 309-348.

17. A. Mills, J. Wang, M. McGrady, Method of rapid assessment of

photocatalytic activities of self-cleaning films, J. Phys. Chem.B,110

(2006) 18324-18331.

18. H. Schmidt, M. Naumann, T.S. Müller, M. Akarsu, Application of

spray techniques for new photocatalytic gradient films on plastics,

Thin Solid Films, 502(2006) 132-137.

19. M. Kroell, M. Pridoehl, G. Zimmermann, L. Pop, S. Odenbach, A.

Hartwig, Magnetic and rheological characterization of novel

ferrofluids, J. Magn. Magn. Mater., 289 (2005) 21-24.

20. M. Yan, T. Mori, J. Zou , J. Drennan , Effect of grain growth on

densification and conductivity of ca-doped CeO2 electrolyte, J. Am.

Ceram. Soc., 92 (2009) 2745-2750.

21. J. Ameta, A. Kumar, R. Ameta, V.K. Sharma, S.C. Ameta,

Synthesis and characterization of CeFeO3 photocatalyst used in

photocatalytic bleaching of gentian violet, J. Iran. Chem. Soc., 6 (2)

(2009) 293-299.

22. K. Nagaveni, M. S. Hegde, N. Ravishankar, G. N. Subbanna, G.

Madras, Synthesis and structure of nanocrystalline TiO2 with lower

212

band gap showing high photocatalytic activity, Langmuir, 20

(2004) 2900-2907.

23. Fatiha Tedjani, Ali Khouider, Hafida Ghoualem, Anaerobic

treatment of a food-processing effluent, Procedia Engineering, 33

(2012) 215–219.

24. O. Bourdjiba, F. Bekkouche, A. Hassaine, R. Djenidi, Impact de la

pollution par les hydrocarburessur la qualité des eauxuséesdans

la region de Skikda, Eur. J. Sci. Res., 26 (2009) 80-90.

25. B. Balamurugan, M. Thirumarimurugan, T. Kannadasan, Anaerobic

degradation of textile dye bath effluent using Halomonas sp.,

Bioresource Technology, 102 (2011) 6365–6369.

26. Anil Kumar, Purnima Dhall, Rita Kumar, Redefining BOD:COD ratio

of pulp mill industrial wastewaters in BOD analysis by formulating a

specific microbial seed, International iodeterioration and

Biodegradation, 64 (2010) 197-202.

27. M. J. Pawar, A. D. Khajone, A. B. Ingale, M. D. Gaonar, Sol-gel

synthesis of nanosized α-Fe2O3 and photodegradation of acid red

114 dye, IJASRT, 3 (2) (2012), 600 – 605.

28. PiaoXu, Guang Ming Zeng, Dan Lian Huang, Chong Ling Feng,

Shuang Hu, Mei Hua Zhao, Cui Lai, Zhen Wei, Chao Huang, Geng

Xin Xie, Zhi Feng Liu, Science of the Total Environment, 424

(2012) 1–10.

213

29. S. Ekambaram, K. C. Patil, M. Maaza, Synthesis of lamp

phosphors: Facile combustion approach, J. Alloys Compd. 393

(2005) 81-92.

30. J. Lee, J.P. Ahn, S.W. Kim, Growth of nanostructured

polycrystalline cerium oxide through a solvothermal precipitation

using near supercritical fluids, J. Nanosci. Nanotechnol., 10 (2010)

130-134.

31. ZHANG Qiu-li, YANG Zhi-mao, DING Bing-jun, LAN Xin-zhe, GUO

Ying-juan, Preparation of copper nanoparticles by chemical

reduction method using potassium borohydride, Trans.Nonferrous

Met. Soc. China, 20(2010) 240−244.

32. GENG Xin-ling, SU Zheng-tao, Research on preparation of

nanocopper powder by liquid-phase method, J. Applied Chemical

Industry, 34(10) (2005) 615−617.

33. Mao-Sung Wu, Pin-Chi J. Chiang, Jyh-Tsung Lee, Jung-Cheng Lin,

Synthesis of manganese oxide electrodes with interconnected

nanowire structure as an anode material for rechargeable lithium

ion batteries, J. Phys. Chem. B, 109 (2005) 23279.

34. L. Carbone, S. Kudera, E. Carlino, W. J. Parak, C. Giannini, R.

Cingolani, L. Manna, Multiple wurtzite twinning in CdTe

nanocrystals induced by methylphosphonic acid, J. Am. Chem.

Soc., 128 (3) (2006) 748-755.

214

35. Kh. Ghanbari, M. F. Mousavi, M. Shamsipur, Preparation of

polyaniline nanofibers and their use as a cathode of aqueous

rechargeable batteries, Electrochim. Acta, 52 (4) (2006) 1514-

1522.

36. R. Gegova, Y. Dimitriev, A. Bachvarova-Nedelcheva, R. Iordanova,

A. Loukanov, Tz. Iliev, Combustion gel method for synthesis of

nanosized ZnO/TiO2 powders, Journal of Chemical Technology and

Metallurgy, 48 (2) (2013) 147-153.

37. Sina Saremi-Yarahmadi, Asif Ali Tahir, B. Vaidhyanathan, K.G.U.

Wijayantha, Fabrication of nanostructured α-Fe2O3 electrodes

using ferrocene for solar hydrogen generation, Materials Letters 63

(2009) 523–526.

38. Gu Jianmin, Li Siheng, Wang Enbo, Li Qiuyu, Sun Guoying,

Xu Rui, Zhang Hong, Single-crystalline α-Fe2O3 with hierarchical

structures: Controllable synthesis, formation mechanism and

photocatalytic properties, J. Solid State Chem. 182 (5) (2009) 265-

1272.

39. L. Gomathi Devi, S. Girish Kumar, K. Mohan Reddy, C.

Munikrishnappa, Photodegradation of methyl orange, an azo dye

by Advanced Fenton Process using zero valent metallic iron:

influence of various reaction parameters and its degradation

mechanism, J. Haz. Mater.164 (2009) 459–467.

215

40. H.M.H. Gad, A.A. El-Sayed, Activated carbon from agriculture by-

products for the removal of rhodamine-B from aqueous solution, J.

Haz. Mater.168 (2-3) (2009) 1070-1081.

41. Dengsong Zhang, Tingting Yan, Chengsi Pan, Liyi Shi, Jianping

Zhang, Carbon nanotube-assisted synthesis and high catalytic

activity of CeO2 hollow nanobeads, Materials Chemistry and

Physics 113 (2009) 527–530.

42. Jiao Hua, Yang Heqing, Thermal decomposition synthesis of 3D

urchin-like α-Fe2O3 superstructures, Mater. Sci. Engg. B 156

(2009) 68–72.

43. Wei Zheng, Zhenyu Li, Hongnan Zhang, Wei Wang, Yu Wang, Ce

Wang, Electrospinning route for α-Fe2O3 ceramic nanofibers and

their gas sensing properties, Materials Research Bulletin 44 (6)

(2009) 1432-1436.

44. Rajesh Kumar, S. Gautam, In-Chul Hwang, Jae Rhung Lee, K.H.

Chaec, Nagesh Thakur, Preparation and characterization of α-

Fe2O3 polyhedral nanocrystals via annealing technique, Materials

Letters 63 (2009) 1047–1050.

45. Xiaoli Xie, Heqing Yang, Fenghua Zhang, Li Li, Junhu Ma, Hua

Jiao, Jianying Zhang, Synthesis of hollow microspheres

constructed with α-Fe2O3 nanorods and their photocatalytic and

magnetic properties, J. Alloys Comp. 477 (2009) 90–99.

216

46. York R. Smith, K. Joseph Antony Raj, Vaidyanathan (Ravi)

Subramanian, B. Viswanathan, Sulfated Fe2O3–TiO2 synthesized

from ilmenite ore: A visible light active photocatalyst, Colloids and

Surfaces A: Physicochem. Eng. Aspects 367 (2010) 140–147.

47. Xiangxin Yang, Chundi Cao, Larry Erickson, Keith Hohn, Ronaldo

Maghirang, Kenneth Klabunde, Photo-catalytic degradation of

rhodamine B on C-, S-, N-, and Fe-doped TiO2 under visible-light

irradiation, Applied Catalysis B: Environmental, 91 (2009) 657–

662.

48. Jiarui Huang, Min Yang, Cuiping Gu, Muheng Zhai, Yufeng Sun,

Jinhuai Liu, Hematite solid and hollow spindles: Selective

synthesis and application in gas sensor and photocatalysis,

Materials Research Bulletin, 46 (2011) 1211–1218.

49. Tanmay K. Ghorai, Soumya K. Biswas, Panchanan Pramanik,

Photooxidation of different organic dyes (RB, MO, TB, and BG)

using Fe(III)-doped TiO2 nanophotocatalyst prepared by novel

chemical method, Applied Surface Science, 254 (2008) 7498–

7504.

50. Slavica Zec, Snezˇana Bosˇkovic´, Branka Kaluperovic´, Z ˇarko

Bogdanov, Nada Popovic, Chemical reduction of nanocrystalline

CeO2 Ceramics International, 35 (2009) 195–198.

217

51. Tianshu Zhang, Peter Hing, Haitao Huang, J. Kilner, Sintering

study on commercial CeO2 powder with small amount of MnO2

doping, Materials Letters, 57 (2002) 507–512.

52. Hongfeng Li, Guanzhong Lu, Qiguang Dai, Yanqin Wang, Yun

Guo, Yanglong Guo, Efficient low-temperature catalytic combustion

of trichloroethylene over flower-like mesoporous Mn-doped CeO2

microspheres, Applied Catalysis B:Environmental, 102 (2011) 475–

483.

53. B.Z. Matović, D.M. Buˇcevac, M. Rosić, B.M. Babić, Z.D.

Dohcević- Mitrović, M.B. Radović, Z.V. Popović, Synthesis and

characterization of Cu-doped ceria nanopowders, Ceramics

International, 37 (8) (2011) 3161-3165.

54. Xiaodong Wu, Shuang Liu, Duan Weng, Fan Lin, Textural–

structural properties and soot oxidation activity of MnOx-CeO2

mixed oxides, Catalysis Communications, 12 (2011) 345–348.

55. R. Dziembaj, M. Molenda, L. Chmielarz, M.M. Zaitz, Z.

Piwowarska, A. Rafalska-Łasocha, Optimization of Cu doped ceria

nanoparticles as catalysts for low-temperature methanol and

ethylene total oxidation, Catalysis Today, 169 (2010) 112-117.

56. Kingkaew Chayakul, Tipaporn Srithanratana, Sunantha

Hengrasmee, Effect of Re addition on the activities of Co/CeO2

catalysts for water gas shift reaction, Journal of Molecular

Catalysis A: Chemical, 340 (2011) 39–47.

218

57. Yang Tian, DiWu, Xiao Jia, Binbin Yu, Sihui Zhan, Core-shell

nanostructure of α-Fe2O3/Fe3O4: synthesis and photocatalysis for

methyl orange, Journal of Nanomaterials, 2011 (2011) 1-5.

58. Y. Wang, C.S. Liu, F.B. Li, C.P. Liu, J.B. Liang, Photodegradation

of polycyclic aromatic hydrocarbon pyrene by iron oxide in solid

phase, J. Hazard. Mater., 162 (2009) 716–723.

59. Gajendra Kumar Pradhan, K. M. Parida, Fabrication of iron-

cerium mixed oxide: an efficient photocatalyst for dye degradation,

IJEST, 2 (9) (2010) 53-65.

60. S. K. Kansal, M. Singh, D, Sud, Studies on photodegradation of

two commercial dyes in aqueous phase using different

photocatalysts, J. Hazard. Mater., 141 (3) (2007) 581-590.

61. AniIdris, Nursia Hassan, Nur Suriani Mohammed Ismail, Effaliza

Misran, Noordin Mohammed Yusof, Audrey-Flore Ngomsik, Agnes

Bee, Photocatalytic magnetic separable beads for chromium(VI)

reduction, Water Research, 44 (2010) 1638-1688.

62. B. David, O. Schneeweiss, E. Santavá, O. Jaek, Magnetic

properties of γ-Fe2O3 nanopowder synthesized by atmospheric

microwave torch discharge, Acta Physica Polonica A, 122 (1)

(2012) 9-11.

63. Hamid Reza Pouretedal, Mina Ahmadi, Synthesis,

characterization, and photocatalytic activity of MCM-41 and MCM-

219

48 impregnated with CeO2 nanoparticles, Int. Nano Lett., 2 (10)

(2012) 1-8.

64. Weiping Wang, Shuijin Yang, Photocatalytic degradation of

organic dye methyl orange with phosphotungstic acid, J. Water

Resource and Protection, 2 (2010) 979-983.

65. Wen Ku Chang, K. Koteswara Rao, Hua Cing Kuo, Jen Fong Cai,

Ming Show Wong, A novel core–shell like composite

In2O3@CaIn2O4 for efficient degradation of methylene blue by

visible light, Applied Catalysis A: General, 321 (2007) 1–6.

66. Hajira Tahir, Fahim Uddin, Development of methods for the

removal of dye using metal-doped alumina catalysts, The Arabian

Journal for Science and Engineering, 32( 2007)149-161.

67. R. M. Mohamed, E. S. Aazam, Synthesis and characterization of

CeO2-SiO2 nanoparticles by microwave-assisted irradiation method

for photocatalytic oxidation of methylene blue dye, International

Journal of Photoenergy, 2012 (2012) 1-9.

68. Gratian R. Bamwenda, Hironori Arakawa, Cerium dioxide as a

photocatalyst for water decomposition to O2 in the presence of

Ce4+aq and Fe3+

aq, Journal of Molecular Catalysis A: Chemical, 161

(2000) 105–113.

69. Juliana Fonseca de Lima, Renata Figueredo Martins, Claúdio

Roberto Neri, Osvaldo Antonio Serra, ZnO:CeO2-based

220

nanopowders with low catalytic activity as UV absorbers, App. Sur.

Sci., 255 (2009) 9006–9009.

70. Ahsanulhaq Qurashi, Zhonghai Zhong, Mir Wakas Alam,

Synthesis and photocatalytic properties of α-Fe2O3 nanoellipsoids,

Solid State Sciences, 12 (2010) 1516-1519.

71. Angus Shiue, Chih-Ming Ma, Ri-Tian Ruan, Chang-Tang Chang,

Adsorption kinetics and isotherms for the removal methyl orange

from wastewaters using copper oxide catalyst prepared by the

waste printed circuit boards, Sustain. Environ. Res., 22 (4) (2012)

209-215.

72. Siham Al-Qaradawi, Salman R. Salman, Photocatalytic degradation

of methyl orange as a model compound, J. Photochem. Photobio.

A: Chemistry, 148 (2002) 161–168.

73. Ke Dai, Hao Chen, Tianyou Peng, Dingning Ke, Huabing Yi,

Photocatalytic degradation of methyl orange in aqueous

suspension of mesoporous titania nanoparticles, Chemosphere,

69 (2007) 1361-1367.

74. M. Soltaninezhad, A. Aminifar, Study on nanostructures of

semiconductor zinc oxide (ZnO) as a photocatalyst for the

degradation of organic pollutants, Int. J. Nano Dim., 2 (2) (2011)

137-145.

75. Jianjun Liao, Shiwei Lin, Li Zhang, Neng Qian Pan, Xiankun Cao,

Jianbao Li, Photocatalytic degradation of methyl orange using a

221

TiO2/Ti mesh electrode with 3D nanotube arrays, ACS Appl. Mater.

Interfaces, 4 (2012) 171−177.

76. Fanming Meng, Ling Cao, Xueping Song, Zhaoqi Sun,

Photocatalytic degradation of methyl orange by nano-TiO2thin

films prepared by RF magnetron sputtering, Chinese Optics

Letters, 7 (10) (2009) 956-959.

77. M. Vinoth, H. Y. Lim, R. Xavier, K. Marimuthu, S. Sreeramanan,

M.H. Mas Rosemal, S. Kathiresan, Removal of methyl orange

from solutions using yam leaf fibers, Int. J. Chem. Tech. Res., 2

(2010) (4) 1892-1900.

78. Suman Koner, Biswajit Kumar Saha, Rahul Kumar, Asok Adak,

Adsorption kinetics and mechanism of methyl orange dye on

modified silica gel factory waste, Int. J. Cur. Res., 33 (6) (2011)

128-133.

79. Kunwar P. Singh, Dinesh Mohan, Sarita Sinha,G. S. Tondon,

Devlina Gosh, Color removal from wastewater using low-cost

activated carbon derived from agricultural waste material, Ind.Eng.

Chem. Res., 42 (2003) 1965-1976.

80. N. Barka, S. Qourzal, A. Assabbane and Y. Ait-Ichou, Kinetic

modeling of the photocatalytic degradation of methyl orange by

supported TiO2, J. Environ. Sci. Engg., 4 (5) (2010) 1-5.

222

81. Xian-Tai Zhou, Hong-Bing Ji, Xing-Jiao Huang, Photocatalytic

degradation of methyl orange over metalloporphyrins supported on

TiO2 Degussa P25, Molecules, 17 (2012) 1149-1158.

82. Xiao Liu, Chunjuan Dong, Simultaneous COD and nitrogen

removal in a micro-aerobic granular sludge reactor for domestic

wastewater treatment, Systems Engineering Procedia, 1 (2011)

99–105.

83. Rani Devi, R.P. Dahiya, COD and BOD removal from domestic

wastewater generated in decentralised sectors, Bioresource

Technology, 99 (2008) 344–349.

84. B. Balamurugan, M. Thirumarimurugan, T. Kannadasan,

Anaerobic degradation of textile dye bath effluent using

Halomonas sp., Bioresource Technology 102 (2011) 6365–6369.

85. Serkan Eker, Fikret Kargi, COD, para-chlorophenol and toxicity

removal from synthetic wastewater using rotating tubes biofilm

reactor (RTBR), Bioresource Technology, 101 (2010) 9020–9024.

86. Francisco Gómez-Rivera, James A. Field, Dustin Brown, Reyes

Sierra-Alvarez, Fate of cerium dioxide (CeO2) nanoparticles in

municipal wastewater during activated sludge treatment,

Bioresource Technology, 108 (2012) 300–304.

87. Jia-Qian Jiang, Alex Panagoulopoulos, Mike Bauer, Pete Pearce,

The application of potassium ferrate for sewage treatment, J.

Environ. Manag., 79 (2006) 215–220.

223

88. Yingjie Hua, Chongtai Wang, Jinyuan Liu, Bin Wang, Xilong Liu,

Chunyan Wu, Xiaoyang Liu, Visible light photocatalytic

degradation of rhodamine B using Fe(III)-substituted

phosphotungstic heteropolyanion, Journal of Molecular Catalysis

A: Chemical, 365 (2012) 8– 14.

89. G.A. Ozin, A.C. Arsenault, Nanochemistry: A chemical approach

to nanomaterials, Royal Society of Chemistry, London, 2005.

90. Mingya Zhong, Guiye Shan, Yajun Li, Guorui Wang, Yichun Liu,

Synthesis and luminescence properties of Eu3+ - doped nO

nanocrystals by a hydrothermal process, Mater. Chem. Phys., 106

(2007) 305-309.

91. Dan Li, Zheng Tong Liu, Yu Hang Leung, Aleksandra B. Djurisic,

Mao Hai Xie, Wai Kin Chan, Transition metal-doped ZnO

nanorods synthesized by chemical methods, J. Phys. Chem.

Solids, 69 (2008) 616-619.

92. Amir Kajbafvala, Mohammad Reza Shayegh, Mahyar Mazloumi,

Saeid Zanganeh, aidin Lak, Matin Sadat Mohajerani, S.K.

Sadrnezhaad, Nanostructured sword-like ZnO wires: rapid

synthesis and characterization through a microwave-assisted

route, J. Alloys Comp., 469 (2009) 293- 297.

93. X. Gao, X. Li, W. Yu, Flowerlike ZnO nanostructures via

hexamethylenetetramine assisted thermolysis of zinc-

224

ethylenediamine complex, J. Phys. Chem. B, 109 (2005) 1155-

1161.

94. J. Cheng, X. Zhang, Z. Luo, Aligned ZnO nanorod arrays fabricated

on Si substrate by solution deposition, Physica E:Low-dimensional

systems and Nanostructures, 31 (2006) 235-239.

95. C.H. Cho, M.H. Han, D.H. Kim, D.K. Kim, Morphology evolution of

anatase TiO2 nanocrystals under a hydrothermal condition

(pH = 9.5) and their ultra-high photo-catalytic activity, Mater.

Chem. Phys., 92 (2005) 104–111.

96. H.M. Cheng, K.F. Lin, H-C. Hsu, C.J. Lin, L.J. Lin, W-F. Hsieh,

Enhanced resonant Raman scattering and electron−phonon

coupling from self-assembled secondary ZnO nanoparticles, J.

Phys. Chem. B, 109 (2005) 18385-18390.

97. A. Zaleska, J.W. Sobczak, E. Grabowska Hupka, Preparation

and photocatalytic activity of boron-modified TiO2under UV and

visible light, J. Appl. Catal. B, 78 (1-2) (2008) 92–100.

98. C.K. Jung, I.S. Bae, Y.H. Song, J. H. Boo, Plasma surface

modification of TiO2 photocatalysts for improvement of catalytic

efficiency, Surf. Coat. Technol., 200 (5-6) (2005) 1320–1324.

99. Chung Ro Lee, Hong Woo Lee, Jae Sung Song, Whong Whoe

Kim, Sun Park, Synthesis and Ag recovery of nanosized ZnO

powder by solution combustion process for photocatalytic

applications, J. Mater. Synth. Pro., 95 (2001) 281-286.

225

100. K. Vanheusden, C.H. Seager, W.L. Warren, D.R. Tallant, J.

Caruso, M.J. Hampdan Smith, T.T. Kodas, Green

photoluminescence efficiency and free-carrier density in ZnO

phosphor powders prepared by spray pyrolysis, J. Lumin., 75

(1997) 11-16.

101. M. A. Barkat, H. Schaeffer, G. Hayes, S. Ismat Shah,

Photocatalytic degradation of 2-chlorophenol by Co-doped TiO2

nanoparticles, App. Catal. B: Environmental, 57 (2004) 23-30.

102. LI Song, Structural design, characterization property investigation

of iron oxide nanoparticles with visible light photoactivity, 2009,

Ph.D. Thesis, pp 36.

103. Y. Wang, W. Du, Y. Xu, Effect of sintering temperature on the

photocatalytic activities and stabilities of hematite and silica-

dispersed hematite particles for organic degradation in aqueous

suspensions, Langmuir, 25 (5) (2009) 2895–2899.

104. M. Hermanek, R. Zboril, I. Medrik, J. Pechousek, C. Gregor,

Catalytic efficiency of iron(III) oxides in decomposition of

hydrogen peroxide: competition between the surface area and

crystallinity of nanoparticles, J. Am. Chem. Soc., 129 (2007)

10929–10936.

105. S.D. Shenoy, P.A. Joy, M.R. Anantharaman, Effect of mechanical

milling on the structural, magnetic and dielectric properties of co-

226

precipitated ultrafine zinc ferrite, J. Magn. Mag. Mater., 269

(2003) 217-226.

106. J.L. Martın, D. Vidales, D.A. Lopez, E. Vila, F.A. Lopez, The effect

of the starting solution on the physico-chemical properties of zinc

ferrite synthesized at low temperature, J. Alloys Compd., 287

(1999) 276-283.

107. K.C. Patil, S.T. Aruna, S. Ekambaram, Combustion Synthesis,

Curr. Opin. Solid State Mater. Sci., 2 (1997) 158-165.

108. K.C. Patil, S.T. Aruna, T. Mimani, Combustion Synthesis: an

update, Curr. Opin. Solid State Mater. Sci., 6 (2002) 507-512.

109. S. Ekambaram, K.C. Patil, M. Maaza, Synthesis of lamp

phosphors: Facile combustion approach, J. Alloys Comp., 393

(2005) 81-92.

110. B.M. Nagabhushana, R.P.S. Chakradhar, K.P. Ramesh, C.

Shivakumara, G.T. Chandrappa, Low temperature synthesis,

structural characterization and zero-field resistivity of

nanocrystalline La1-xSrxMnO3+δ (0≤x≤0.3) manganites, Mater.

Res. Bull., 41 (2006) 1735-1746.

111. B.M. Nagabhushana, G.T. Chandrappa, R.P.S. Chakradhar, K.P.

Ramesh, C. Shivakumara, Synthesis, structural and transport

properties of nanocrystalline La1-xSrxMnO3 (0≤x≤0.3) powders,

Solid State Commun., 136 (2005) 427-432.

227

112. B.M. Nagabhushana, R.P.S. Chakradhar, K.P. Ramesh, C.

Shivakumara, G.T. Chandrappa, Combustion synthesis,

characterization and metal-insulator transition studies of

nanocrystalline La1-xSrxMnO3 (0≤x≤0.3), Mater. Chem. Phys., 102

(2007) 47-52.

113. R. Nagaraja, C.R.Girija, B.M.Nagabhushana, N. Donappa, K.M.

Sastry, Solution combustion synthesis, characterization and

photocatalytic activity of nanosized ZnO catalyst for textile

industrial dye effluent degradation, Asian J. Chem. 23 (11) (2011)

5040-5044.

114. A.A. Jahagirdar, M.N. Zulfiqar Ahmed, N. Donappa, H.

Nagabhushana, B.M. Nagabhushana, Solution combustion

synthesis and photocatalytic activity of α-Fe2O3 nanopowder,

Trans. Ind. Cer. Soc., 70 (3) (2011) 159-162.

115. J.H. Bai, J.C. Liu, Solution combustion synthesis and sintering

behavior of porous MgAl2O4 powders, Science of Sintering, 42

(2010) 133-141.

116. Sheetal, S.P. Khatkar, Rajni Arora, V.B. Taxak, Mandeep, Solution

combustion synthesis and structural properties of YSrAl3O7: Tb

nanoparticles, Int. J. Biotech. Bioengg. Res., 4 (4) (2013) 291-

298.

117. A. CuÈneyt Tas, Combustion synthesis of calcium phosphate

bioceramic powders, J. Eur. Cer. Soc., 20 (2000) 2389-2394.

228

118. S.T. Aruna, A.S. Mukasyan, Combustion synthesis and

nanomaterials, Curr. Opi. Solid State Mater. Sci., 12 (2008) 44–50.

119. K. Christine Stella, A. Samson Nesaraj, Effect of fuels on the

combustion synthesis of NiAl2O4 spinel particles, Iran. J. Mater.Sci.

Engg., 7 (2) (2010) 36-44.

120. Klaus-Dieter Liss, Arno Bartels, Andreas Schreyer, Helmut

Clemens, High-energy X-rays: A tool for advanced bulk

investigations in materials science and physics, Textures and

Microstructures, 35 (2003) 219–252.

121. P. Klug, L.E Alexander, X-ray Diffraction Procedure, Wiley, New

York, 1954.

122. J. Hua, J. Gengsheng, Hydrothermal synthesis and

characterization of monodisperse α-Fe2O3 nanoparticles,

Materials Letters, 63 (2009) 2725-2777.

123. G. Wang, Q. Mu, T. Chen, Y. Wang, Synthesis, characterization

and photoluminescence of CeO2 nanoparticles by a facile method

at room temperature, J. Alloys. Compd., 493 (2010) 202-207.

124. G. K. William, W. H. Hall, X-ray line broadening from filed

aluminium and wolfram, Acta Metall., 1 (1953) 22–31.

125. R.W.G. Wyckoff, Crystal Structures, vol. 2, Interscience, New York,

1964. pp. 4–5.

126. A.A. Jahagirdar, N. Dhananjaya, D.L. Monika, C.R. Kesavulau,

H. Nagabhushana, S.C. Sharma, B.M. Nagabhushana, C.

229

Shivakumara, J.L. Rao, R.P.S. Chakradhar, Structural, EPR,

optical and magnetic properties of α-Fe2O3 nanoparticles,

Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, 104 (2013) 512-518.

127. 0. Laurianne Truffault, Minh-Tri Ta, Thierry Devers, Konstantin

Konstantinov, Vale´rie Harel, Cyriaque Simmonard, Caroline

Andreazza, Ivan P. Nevirkovets, Alain Pineau, Olivier Veron, Jean-

Philippe Blondeau, Application of nanostructured Ca doped CeO2

for ultraviolet filtration, Materials Research Bulletin, 45 (2010)

527–535.

128. A. Jagannatha Reddy, M.K. Kokila, H. Nagabhushana, J.L. Rao,

C.Shivakumara, B.M. Nagabhushana, R.P.S. Chakradhar,

Combustion synthesis, Characterization and Raman Studies of

ZnO nanopowders, Spectrochimica Acta Part A: Molecular and

Biomolecular Spectroscopy, 81 (1) (2011) 53-58.

129. A.A.Jahagirdar, M.N.Zulfiqar Ahmed, N. Donappa,

H.Nagabhushana, B.M. Nagabhushana, Synthesis,

characterization and dye degradation activity of α-Fe2O3, IJETA-

ETS, 4 (2) (2011) 144-147.

130. B.S. Zou, W. Huang, M.Y. Han, S.F.Y. Li, X.C. Wu, Y. Zhang, J.

Zhang, J.S. Zhang, P.F. Wu, R.Y. Wang, Anomalous optical

properties and electron-phonon coupling enhancement in Fe2O3

230

nanoparticles coated with a layer of stearates, J. Phys. Chem.

Solids, 58 (1997) 1315–1320.

131. Y.Y. Xu, D. Zhao, X.J. Zhang, W.T. Jin, P. Kashkarov, H. Zhang,

Synthesis and characterization of single-crystalline α-Fe2O3

nanoleaves, Physica E, 41(2009) 806–811.

132. G. Zhang, Y. Xu, D. Gao, Y. Sun, α-Fe2O3 nanoplates: PEG-600

assisted hydrothermal synthesis and formation mechanism J.

Alloys Compd., 509 (2011) 885–890.

133. C. Ho, J.C. Yu, T. Kwong, A.C. Mak, S. Lai, Morphology-

Controllable Synthesis of Mesoporous CeO2 Nano- and

Microstructures Chem. Mater., 17 (2005) 4514-4522.

134. H. Nagabhushana, B.M. Nagabhushana, M. Kumar, H.B. Prem

Kumar, C. Shivakumara, R.P.S. Chakradhar, Synthesis,

characterization and photoluminescence properties of CaSiO3:

Dy3+ nanophosphors, Phil. Mag., (90) 26 (2010) 3567–3579.

135. S. Tsunekawa, T. Fukuda, A. Kasuya, Blue shift in ultraviolet

absorption spectra of monodisperse CeO2-x nanoparticles, J. Appl.

Phys., 87 (2000) 1318–1321.

136. Haosheng Fei, Xicheng Ai, Mingyuan Gao, Yanqiang Yang, tieqiao

Zhang, Jiancong Shen, Luminescence of coated α-Fe2O3

anoparticles, J. Lumin., 66 (1996) 345-348.

231

137. X. Lu, X. Li, F. Chen, C. Ni, Z. Chen, Hydrothermal synthesis of

prism-like mesocrystal CeO2, J. Alloys Compd., 476 (2009) 958–

962.

138. S.J. Gregg, K.S.W. Sing, Adsorption, surface area and porosity,

Academic, London, 1997, p. 111.

139. S. Brunauer, L. Deming, W.E. Deming, On a theory of the Vander

Waals adsorption of gases, J. Am. Chem. Soc., 62 (1940) 1723-

1732.

140. G.L. Miessler, D.a. Tarr, Inorganic Chemistry; Prentice-Hall Inc.,

New Jersey, 1999.

141. D.F. Shriver, P.W Atkins, Inorganic Chemistry; Oxford University

Press, Oxford, 1999.

142. Y. Hu, H.L. Tsai, C.L. Huangk, Effect of brookite phase on the

anatase–rutile transition in titania nanoparticles, Eur. Ceram. Soc.,

23 (5) (2003) 691-696.

143. Y. Shao, D. Tang, J. Sun, Y. Lee, W. Xiong, Lattice deformation

and phase transformation from nano-scale anatase to nano-scale

rutile TiO2 prepared by a sol-gel technique, China Particuology, 2

(3) 2004, 119-123.

144. A. Testino, I.R. Bellobono, V. Buscaglia, C. Canevali, M. D'Arienzo,

S. Polizzi, R. Scotti, F. Morazzoni, Optimizing the photocatalytic

properties of hydrothermal TiO2 by the control of phase

232

composition and particle morphology: a systematic approach, J.

Am. Chem. Soc., 129 (12) (2007) 3564–3575.

145. T. Tachikawa, M. Fujitsuka, T. Majima, Mechanistic Insight into the

TiO2 photocatalytic reactions:� design of new photocatalysts, J.

Phys. Chem. C, 111 (14) (2007) 5259-5275.

146. P.D. Cozzoli, R. Comparelli, E. Fanizza, M.L. Curri, A. Agostiano,

Photocatalytic activity of organic-capped anatase TiO2 nanocrystals

in homogeneous organic solutions, Mat. Sci. Engg. C, 23 (6-8)

(2003) 707-713.

147. R. Daghrira, P. Droguia, D. Robert, Photoelectrocatalytic

chnologies for environmental applications, J. Photochem. Photobio.

A: Chemistry, 238 (2012) 41– 52.

148. O. Carp, C.L. Huisman, A. Reller, Photoinduced reactivity of

titanium dioxide, Progress in Solid State Chem., 32 (1-2) (2004) 33-

177.

149. T. Hirakawa, P.V. Kamat, Charge separation and catalytic activity

of Ag/TiO2 core shell composite clusters under UV-irradiation, J.

Amer. Chem. Soc., 127 (2005) 3928-3934.

150. N. Serpone, Relative photonic efficiencies and quantum yields in

heterogeneous photocatalysis, J. Photochem. Photobiol. A:

Chemistry, 104 (1-3) (1997) 1-12.

151. N. Serpone, D. Lawless, R. Khairutdinov, Size effects on the

photophysical properties of colloidal anatase TiO2 particles: size

233

quantization versus direct transitions in this indirect semiconductor

?, J. Phys. Chem., 99 (45) (1999) 16646-16654.

152. Rajeev Jain, Shalini Sikarwar, Photodestruction and COD removal

of toxic dye erioglaucine by TiO2-UV process: influence of

operational parameters, Int. J. Phy. Sci., 3 (12) (2008) 299-305.

153. M.N. Rashed, A.A. El-Amin, Photocatalytic degradation of ethyl

orange in aqueous TiO2 under different solar irradiation sources,

Int. J. Phy. Sci., 2 (3) (2007) 73-81.

154. V.C. Srivastava, I.D. Mall, I.M. Mishra, Treatment of pulp and

paper mill wastewaters with poly aluminium chloride and bagasse

fly ash, Colloids and Surfaces A: Physico Chem. Engg. Aspects,

260 (1-3) (2005) 17-28.

155. R D. Pokhrel, T. Viraraghavan , Treatment of pulp and paper mill

wastewater: a review, Science of the Total Environment, 333 (1-3)

(2004) 37-58.

156. Alexandra M.E. Viana da Silva, Ricardo J.N. Bettencourt da Silva,

M. Filomena, G.F.C. Camoes, Optimization of the determination of

chemical oxygen demand in wastewaters, Analytica Chimica Acta,

699 (2011) 161–169.

157. M.C. Diez, M.L. Mora, S. Videla, Adsorption of phenolic

compounds and color from bleached Kraft mill effluent using

allophanic compounds, Wat. Res., 33 (1) (1999) 125-130.

234

158. V. S. Mishra, V. V. Mahajani, J. B. Joshi, Wet Air Oxidation, Ind.

Eng. Chem. Res., 34 (1995) 2-48.

159. A. Garg, I. Mishra, S. Chand, Thermochemical Precipitation as a

pretreatment step for the chemical oxygen demand and color

removal from pulp and paper mill effluent, Ind. Eng. Chem. Res.,

44 (7) (2005) 2016-2026.

160. K.R. Munkittrick, M.R. Servos, J.H. Carey, G.J. Van Der Kraak,

Environmental impacts of pulp and paper wastewater: evidence for

a reduction in environmental e€ects at North American pulp mills

since 1992, Water Sci. Technol., 35 (1997) 329-338.

161. Zhimin Fu, Yugao Zhang, Xiaojun Wang, Textiles wastewater

treatment using anoxic filter bed and biological wriggle bed-ozone

biological aerated filter, Bioresource Technology, 102 (2011)

3748–3753.

162. Sayeda M. Ali, Shawky Z. Sabae, Mohammed Fayez, Mohammed

Monib, Nabil A. Hegazi, The influence of agro-industrial effluents

on River Nile pollution, Journal of Advanced Research, 2 (2011)

85–95.

163. B.S. Shankar, N. Balasubramanya, M.T. Maruthesa Reddy,

Hydrochemical assessment of the pollutants in ground waters of

Vrishbhavathi Valley Basin in Bangalore (India), J. Environ. Sci.

Engg., 50 (2) (2008) 97-102.

235

164. M.V. Ahipathy, E.T. Puttaiah, Toxicity of Vrishabhavathy river

water and sediment to the growth of phaseolus vulgharis (french

beans), J. Appl. Sci. Environ. Manag., (11 (7) (2007) 17–26.

165. S. L. Clesceri, A. E. Greenberg, A. D. Eaton, Standard Methods for

the Examination of Water and Waste Water, 20th Edition, APHA,

AWWA, WEF, Washington DC Sample collection and preservation

pp.1.27-1.34, pH COD pp.4-81, sulphates pp.4-178, alkalinity

pp.2-24-28, (1998).

166. R. Madhukar, S. Srikantaswamy, Impact of industrial effluent on

the water quality of Vrishbhavathi River and Byramangala Lake in

Bidadi Industrial Area, Karnataka, India, International Journal of

Geology, Earth & Environmental Sciences, 3 (2) (2013) 132-141.

167. I.B. Singh, M. Prasad, Study on the fluoride removal characteristics

of mineral (fluorapatite), Indian J. Chem. Technol., 11 (2004) 185-

189.

168. The Environmental (Protection) Rules, 1986, CPCB (Govt. of

India) Pollution Control Series: PCL/2/1992, Volume I .298 (1995).

List of Publications 1. A.A. Jahagirdar, M.N. Zulfiqar Ahmed, N.Donappa , H.

Nagabhushana , B.M. Nagabhushana “Solution Combustion Synthesis and Photocatalytic Activity of α-Fe2O3” National Journal of Indian Ceramic Society, (2011),vol. 703, 159-162.

2. A.A.Jahagirdar, M.N. Zulfiqar Ahmed, N.Donappa, H. Nagabhushana , B.M. Nagabhushana. “Synthesis, Characterization and Dye Degradation Activity Of α-Fe2O3” International Journal of Emerging Technology and Applications in Engineering, Technology and Sciences WASSN: 0974-3588 (2011)Vol. 4, Wassue 2 144-148

3. A.A.Jahagirdar, M.N. Zulfiqar Ahmed, N.Donappa, H. Nagabhushana, B.M. Nagabhushana .“COD Removal of Industrial Effluent using Nano Crystalline Ceria Synthesised by Solution combustion method”, IOSR Journal of applied Chemwastry,WASSN:2278-5736,(2012),Vol.1(2), 14-17,

4. A. A. Jahagirdar, N. Dhananjaya, H.Nagabhushana , B.M. Nagabhushana, R. P. S. Chakradhar. “Structural EPR, Optical and Magnetic properties of α-Fe2O3 nano particles”, Spectrochemica Acta Part A Molecular and Bio molecular Spectroscopy, ELSEVIER Vol.104,( 2013), 512-518.

5 Durga Prasad, A. A. Jahagirdar, C. R. Girija, B. M. Nabhushana “Cytotoxicity of CeO2 Nanoparticles for Gram Negative, Gram Positive Bacteria: Antibacterial Effect” Nano Trends: A Journal of Nanotechnology and Its Application Vol.15(1), WASSN: 0973-418X, 7-13

List of papers presented in Conferences

1 “Characterization of nano crystalline LaMnO3powder and its applications in removal of COD” research paper was presented at International conference on active/smart materials, by Department of Physics, Thiagarajar College Of Engineering, Madhurai, Tamilnadu, during Jan 7-9 2009.

2. “Combustion synthesis and luminescent properties of CeO2: Eu phosphor” National conference on luminescence and its applications Central Glass and Ceramics research Institute, Kolkatta,Feb.19-21, 2009.

3. “Combustion synthesis of nano CeO2& its potential application in photo catalysis & COD removal” presented at National conference on Advances in nano materials, Devices & Technology by Dept. of Physics, S V Degree College. Kadapa, Andhra Pradesh July 11-12, 2009. “Received first Best Paper Award”

4. “Studies on Al 2O3:Cr3+ phosphor obtained by combustion process” was presented at National Seminar on Display Phosphor & its applications by Dept.of Physics,Vivekananda Degree College, Bangalore-55. During Oct 22-23, 2009.

5. “Synthesis, Characterization, EPR & Magnetic properties of α-Fe2O3 Nano tripods” was presented at International conference on current trends in Chemistry & Biochemistry by Dept. of Chemistry & Biochemistry, Bangalore University, Bangalore. During Dec 18-19, 2009.

6. “Synthesis, of Nano α-Fe2O3 & its ability to Degrade Dye from waste water, International conference on Water, Plumbing, Sanitation & Health issues & challenges-A trance disciplinary approach, AT Dept. of Civil Engg. Zoology, Bangalore University, Bangalore.Oct 04-05 2010 page 112-115

7. “Synthesis EPR studies of nanocrystalline α-Fe2O3 prepared by low temperature solution combustion techniques” presented at National Conference on recent advances in chemical and environmental sciences at Dept. of basic Sciences – Jain University, Ramanagara, Karnataka, India and Prof. C. N. R. Rao centre for advance materials research, Tumkur University, Karnataka, India.

8. “Photocatalytic Degradation of Rhodamine - B using α-Fe2O3”

presented at Recent advances in Functionalized Materials.by Dept. of Chemistry, M S R I T, Bangalore. During 24-25 Jan 2012.

9. “COD removal of an Industrial effluent using CeO2 nanopowder” was presented at Recent advances in Functionalized Materials.by Dept. of Chemistry, M S R I T, Bangalore. During 24-25 Jan 2012.



1. A number of less expensive metal oxides such as ZnO, SnO2,

CuO etc. can be synthesized by solution combustion synthesis using

the respective metal nitrate and different fuels.

2. The efficiency of the metal oxides as photocatalysts in the removal of

dyes and other organic pollutants from waste waters can be studied.

3. The feasibility of the metal oxides in the removal of dyes by adsorption

can also be studied.

4. The feasibility of the metal oxides as adsorbents in the removal of

heavy metal ions such as Cr, Hg, Cd etc. from industrial wastewaters

can also be studied.

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