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SYNTHESIS AND CHARACTERIZATION OF SOME NEW AND NOVEL ION
EXCHANGE MATERIALS
DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF THE DEGREE OF
iWaiBiter of ^ijilosoptjp er IN
Applied Chemistry t I %,M
^ . \ \' - V
BY
ARUN AGRAWAL
DEPARTMENT OF APPLIED CHEMISTRY FACULTY OF ENGINEERING & TECHNOLOGY
ALIGARH MUSLIM UNIVERSITY ALIGARH ONDIA)
2004
r DS-M-ZC]
^ > ••'^..1 I
5 APR 2035
DS3426
Qt ((X. : 0571-700920-23 Ext. 456 r IRes.: 0571-701881 Emai. chairmanacd@bhara(mail.cofn
D E P A R T M E N T OF APPLIED CHEMISTRY
Samiullah Khan M.Sc, Ph D.
Professor d Chairman
FACULTY OF ENGINEERING & TECHNOLOGY ALI6ARH MUSLIM UNIVERSITY
ALIGARH - 202002 (INDIA)
M"- X^-o'].oii
CERTIFICATE
This is to certify that the work presented in this dissertation entit led
"Synthesis and Characterization of some New and Novel Ion-Exchange
Materials" has been carried out by Mr. Arun Agrawal. It is an original
contribution of the candidate and is suitable for submission for the award of
M. Phil degree in Applied Chemistry.
Prof. S.U. KharT^ (Supervisor & Chairman)
Prof. (Dr.) K. G. Varshney Ph.D.,D.Sc
'Emeritus TeOxrw (AICI^)
JippRedCfieTnistTy (Department
AGgarh Muslim Vniversity
JiGgarfi-202002
reC : (0571) 2700920'Ext.:3001
cDaud.....g^...j.<:^..JMk
CERTIFICATE
This is to certify that the work presented in this dissertation entitled
"Synthesis and Characterization of some New and Novel Ion-Exchange
Materials" has been carried out by Mr. Arun Agrawal under my guidance. It is
an original contribution of the candidate and is suitable for submission for the
award of M. Phil degree in Applied Chemistry.
Prof. K.G. Varshney Emeritus Fellow (AiCTE)
^si. :S:KA9eri SA^A^, 18/158, (Pa^Sarai, A^id<^rh-202001
^eC. : 0571-2411931 MoSiCe : 9412172929
e-maiC: roma [email protected]
ACKNOWLEDGEMENT
All praises to the God, the most merciful and beneficent whose
benedictions made me capable to face all obstacles and accomplish this task
inspite of all constraints.
I take this opportunity to record my deep gratitude to my supervisor
Prof. K.G. Varsheny, Ph.D., D.Sc, Emeritus Professor, for offering me to work
in this prime area of research "Fibrous Ion-Exchangers" and provided invaluable
guidance, constant encouragement, extensive suggestions and freedom in a i
aspects during the entire tenure of this work. I am grateful to him for his
personal interest, the attention and care shown towards me in shaping nty
career.
I wish to express my heartfelt thanks to Prof. S.U. Khan, Chairman,
Department of Applied Chemistry, Aligarh Muslim University, Aligarh, for his
wholehearted interest and encouragement throughout my research career. His
suggestions, fruitful discussions and constructive criticism, have helped in
building up this work.
I owe a word of thanks to Prof. A.K. Singh, Department of Chemistry,
l.l.T, New Delhi, for providing necessary research facilities. I record my special
thanks to Dr. M. Drabik, Institute of Inorganic Chemistry, Slovak Academy of
Sciences, Bratislava, Slovakia for their help in TGA/DTA studies on the materials
under investigation. Thanks are also due, to the Institute Instrumentation Centre,
l.l.T, Roorkee for providing Thermogravimetric and X-ray diffraction spectra,
to All India Institute of Medical Sciences, New Delhi for scanning electron
microscopic study and to Regional sophisticated Instrumentation Centre, Central
Drug Research Institute, Lucknow for providing C, H, N analysis data.
Finally, the sustained interest, unfailing and even enduring affection shown
towards me by my parents deserve a special mention without which it would
not be possible for me to complete this endeavour.
XhLuyy - ^ p - ^ (Arun /(^ra)w a l ) ' '
CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF PUBLICATIONS
LIST OF PAPERS PRESENTED IN CONFERENCE/CONVENTION
CHAPTER 1
General Introduction
References
Page Number
ii
i i i
iv
1-40
41-50
CHAPTER 2 Synthesis, Characterization and Thermal behaviour of 51 -73 Pectin based Cerium (IV) and Thorium (IV) Phosphates as Novel Hybrid Fibrous ion-Exchangers
Introduction 51
Experimental 52
Results and Discussion 69
References 73
LIST OF TABLES
Table Number
Description
Table 1.1 Analytical techniques and principal applications.
Table 1.2 A classification of the principal chromatographic
techniques.
Table 1.3 Stages of development of ion exchangers and
sorbents.
Table 1.4 Principal classes of inorganic ion exchangers.
Table 2.1 Synthesis of various samples of pectin based
cerium (IV) phosphate.
Table 2.2 Synthesis of various samples of pectin based
thorium (IV) phosphate.
Table 2.3 Ion exchange capacity of pectin based cerium (IV)
and thorium (IV) phosphates for various metal
solutions.
Table 2.4 Concentration behaviour of pectin based cerium
(IV) and thorium (IV) phosphates.
Table 2.5 Values of ion exchange capacity of pectin based
cerium (IV) and thorium (IV) phosphates on
recycling.
Table 2.6 Thermal stability of pectin based cerium (IV) and
thorium (IV) phosphates after heating to various
temperatures for 1 h.
Page Number
4
5
10
18
54
55
56
58
60
63
(i)
LIST OF FIGURES
Figure Number Fig.1.1
Fig.1.2
Fig.2.1
Fig.2.2
Fig.2.3
Fig.2.4
Fig.2.5
Fig.2.6
Fig.2.7
Fig.2.8
Fig.2.9
Fig.2.10
Fig.2.11
Fig.2.12
Description
Variants of application of ion-exchange fibres
(lEF) in liquid and gaseous processes.
A technological scheme for preparation of Fiban
ion-exchangers.
Histogram showing the elution behaviour of
pectin based cerium (IV) phosphate.
Histogram showing the elution behaviour of
pectin based thorium (IV) phosphate.
Equilibrium pH titration curves of pectin based
cerium (IV) phosphate.
Equilibrium pH titration curves of pectin based
thorium (IV) phosphate.
Thermogravimetric analysis curve of pectin based
cerium (IV) phosphate.
Thermogravimetric analysis curve of pectin based
thorium (IV) phosphate.
Electron micrograph of pectin based cerium (IV)
phosphate at lOOOx magnification.
Electron micrograph of pectin based thorium (IV)
phosphate at 2000x magnification.
Infrared spectrum of pectin based cerium (IV)
phosphate.
Infrared spectrum of pectin based thorium (IV)
phosphate.
X-ray diffraction pattern of pectin based cerium
(IV) phosphate.
X-ray diffraction pattern of pectin based thorium
(IV) phosphate.
Page Number
23
26
59
59
62
62
64
64
66
66
" 6 7
67
68
68
(ii)
LIST OF PUBLICATIONS
1. Synthetic and Ion-Exchange Studies on a Lead Selective
Acrylamide Thoriunn (IV) Phosphate Hybrid Fibrous Ion-
Exchanger.
K.G. Varshney, Puja Gupta & Arun Agrawal
(Proceedings of National Symposium on Biochemical
Sciences: Health and Environmental Aspects, Allied
Publishers, New Delhi, pp.254-257, 2003).
2. Synthesis, Ion-Exchange and Physico-Chemical Studies on a
Polystyrene Cerium (IV) Phosphate Hybrid Fibrous Ion
Exchanger.
K.G. Varshney, N. Tayal, P. Gupta, Arun Agrawal & M. Drabik
Indian Journal of Chemistry (New Delhi)
(Accepted)
3. Synthesis, Characterization and Thermal behaviour of Pectin
based Cerium (IV) and Thorium (IV) Phosphates as Novel
Hybrid Fibrous Ion Exchangers.
K.G. Varshney, Arun Agrawal & S. Mojumdar
Journal of Thermal Analysis and Calorimetry (Hungary)
(Communicated)
(iii)
LIST OF PAPERS PRESENTED IN CONFERENCE/CONVENTION
1. "Pectin based Thorium (IV) Phosphate as a new and novel
ion-exchange material: Synthesis and Characterization", IT'^
Annual Conference of Indian Council of Chemists, Oct 17-19,
2003, Indian Institute of Technology, Roorkee, India.
2. "Synthesis, Characterization and Ion-Exchange behaviour of
Styrene based Cerium (IV) Phosphate as a new fibrous cation
exchanger", 40^ Annual Convention of Chemists, Dec 23-27,
2003, Bundelkhand University, Jhansi, India.
* The above paper has been selected for Upadhyayula Annapurna
and Satyanarayana Memorial Award in Analytical and
Environmental Chemistry Section.
3. "Synthetic and Ion-Exchange Studies on a Lead selective
Acrylamide Thorium (IV) Phosphate Hybrid Fibrous Ion-
Exchanger", National Symposium on Biochemical Sciences:
Health and Environmental Aspects (BSHEA-2003), Oct 2-4, 2003,
Dayalbagh Educational Institute, Dayalbagh, Agra, India.
(iv)
fk ~ - ^
CHAPTER 1
GENERAL INTRODUCTION
^
Analytical chemistry involves the application of a range of techniques
and methodologies to obtain and assess qualitative, quantitative and structural
information on the nature of matter.
• Qualitative analysis is the identification of elements, species and / or
compounds present in a sample.
• Quantitative analysis is the determination of the absolute or relative
amounts of elements, species or compounds present in a sample.
• Structure analysis is the determination of the spatial arrangement of
atoms in an element or molecule or the identification of characteristic
groups of atoms (functional groups).
The gathering and interpretation of qualitative, quantitative and
structural information is essential to many aspects of human endeavor, both
terrestrial and extra-terrestrial. The maintenance of, and improvement in, the
quality of life throughout the world, and the management of resources rely
heavily on the information provided by chemical analysis. Manufacturing
industries use analytical data to monitor the quality of raw materials,
intermediates and finished products. Progress and research in many areas is
dependent on establishing the chemical composition of man made or natural
materials, and the monitoring of toxic substances in the environment is of ever
increasing importance. Studies of biological and other complex systems are
supported by the collection of large amounts of analytical data.
Important areas of application include the following:
• Quality control: In many manufacturing industries, the chemical
composition of raw materials, intermediates and finished products needs
to be monitored to ensure satisfactory quality and consistency.
• Monitoring and control of pollutants: The presence of toxic heavy
metals (e.g. lead, cadmium and mercury), organic chemicals (e.g.
polychlorinated biphenyls and detergents) and vehicle exhaust gases
(oxides of carbon, nitrogen and sulphur, and hydrocarbons) in the
environment are health hazards that need to be monitored by sensitive
and accurate methods of analysis, and remedial action taken.
• Clinical and biological studies: The levels of important nutrients,
including trace metals (e.g. sodium, potassium, calcium and zinc),
naturally produced chemicals, such as cholesterol, sugars and urea, and
administered drugs in the body fluids of patients undergoing hospital
treatment require monitoring.
• Fundamental and applied research: The chemical composition and
structure of materials used in or developed during research programs in
numerous disciplines can be of significance. Where new drugs or
materials with potential commercial value arc synthesi/cd, a complete
chemical characterization may be required involving considerable
analytical work.
There are numerous chemical or physico-chemical processes that can be
used to provide analytical information. The processes are related to a wide
range of atomic and molecular properties and phenomena thai enable elements
and compounds to be detected and / or quantitatively measured under
controlled conditions. Table 1.1 shows major analytical techniques and
applications.
It is of primary concern of an analytical chemist to separate different
constituents of a sample prior to chemical analysis. Besides the classical
separation methods such as fractional distillation, extraction, filtration,
selective precipitation, osmosis, reverse osmosis, crystallization, dialysis,
diffusion etc., which involves long and complicated operation.
Chromatography especially ion exchange chromatography have been emerged
as a most useful and versatile analytical technique. They have played a
significant role in identification, separation and quantitative determination of
ionic and non-ionic species and purification of chemical compounds.
Chromatographic techniques can be classified according to whether the
separation takes place on a planar surface or in column. They can be further
subdivided into gas and liquid chromatography, and by the physical form, solid
or liquids, of the stationar>' phase and the nature of interactions of solutes with
it, known as sorption mechanisms. Table 1.2 lists ihc most important forms of
chromatography, each based on different combinations of stationary and
mobile phases.
Table 1.1: Analytical techniques and principal applications.
s. No.
1.
2.
3.
4.
5.
6.
7.
8.
Technique
Gravimetry
Titrimetry
Atomic and
molecular
spectrometry
Mass
spectrometry
Chromatography
and
electrophoresis
Thermal analysis
lilectro-chemical
analysis
Radiochemical
analysis
Property measured
Weight of pure analyte or
compound of known stoichiometry
Volume of standard reagent
solution reacting with the analyte
Wavelength and intensity of
electromagnetic radiation emitted
or absorbed by the analyte
Mass of analyte or fragments of it
Various physico-chemical
properties of separated analytes
Chemical/physical changes in the
analyte when heated or cooled
Electrical properties of the analyte
in solution
Characteristic ionizing nuclear
radiation emitted by the analyte
Principal areas of
application
Quantitative for major or
minor components
Quantitative for major or
minor components
Qualitative, Quantative
or structural for major
down to trace level
components.
Qualitative or structural
for major down to trace
level components isotope
ratio
Qualitative and
quantitative separations
of mixtures at major to
trace levels
Characterization of single
or mixed major/minor
components
Qualitative and
quantitative for major to
trace level components
Qualitative and
quantitative at major to
trace levels
Table 1.2: A classification of the principal chromatographic techniques.
S.No.
1.
2.
Technique
Paper chromatography (PC)
Thin layer chromatography (TLC)
Stationary phase Paper (Cellulose)
Silica, cellulose, ion exchange resin, controlled porosity solid
Mobile phase Liquid
Liquid
Format
Planar
Planar
Principal sorption mechanism Partition (adsorption, ion-exchange, exclusion). Adsorption (partition, ion-exchange, exclusion)
Gas Chromatography (GC)
3.
4.
Gas-liquid chromatography (GLC) Gas-solid chromatography (GSC)
Liquid
Solid
Gas
Gas
Column
Column
Partition
Adsorption
Liquid Chromatography (LC)
5.
6.
7.
8.
9.
High performance liquid chromatography (HPLC) Size-exclusion chromatography (SEC) Ion-exchange chromatography (lEC) Ion chromatography (IC) Chiral chromatography (CC)
Solid or bonded phase
Controlled porosity solid
Ion exchange resin or bonded-phase Ion exchange resin or bonded-phase Solid chiral selector
Liquid
Liquid
Liquid
Liquid
Liquid
Column
Column
Column
Column
Column
Modified partition (adsorption)
Exclusion
Ion-exchange
Ion-exchange
Selective adsorption
"Corpora non agunt nisifluida sive solutd" - i.e. substances do not react unless
in a liquid or dissolved state. This ancient empirical rule is not universal. One
of the noteworthy exceptions is ion exchange. Here a solid reacts with a
solution. Ions can be exchanged and electrolytes and even precipitates can be
removed by treating the solution with a solid ion exchanger.
Ion exchange is one of the most important analytical techniques used for
the separation of ionic species. In a true ion exchange process the exchange of
ions takes place stoichiometrically between the stationary and mobile phases as
follows:
R-A + B (aq)^ ' R-B + A (aq)
Where 'A' and 'B' are the replaceable ions, 'R' is the structural unit (matrix) of
the ion exchanger and 'aq' stands for the aqueous phase. The ion exchange
process is reversible i.e. it can be reversed by suitably changing the
concentration of the ions in the solution. The process is thus in many respects
analogous to the adsorption process but is not exactly the same. The
characteristic difference between the two processes is that, the ion exchange
takes place stoichiometrically, really by the effective exchange of ions, while in
adsorption the adsorbent takes up the dissolved substances from the solution
without releasing anything into the solution. However the two processes may
occur simultaneously in practice, particularly in inorganic ion exchangers.
Ion exchange has an interesting historical background. Many million
years ago this phenomenon was noticed in various sections of the globe. The
earliest of the reference [1] were found in the Holy bible establishing Moses
6
priority that succeeded in preparing drinking water from brackish water by an
ion exchange technique. About thousands year later, Aristotle stated the
seawater loses part of its salt content when percolating through certain sands
[2]. Subsequent to this time, only scare references are found until in 1980.
Thomson [3] and Way [4], two English Chemists, rediscovered "base
exchange" (cation exchange) in soils. The materials that are responsible for
these phenomena were identified chiefly by Lemberg [5] and later by Wiegner
[6] as clays, glauconites, zeolites, and humic acids. These discoveries led to
attempts to use such materials in plant operations for water softening and other
purposes and to synthesize products with similar properties. The first synthetic
industrial ion exchangers were prepared in 1903 by Harms and Rumplcr [7],
two German Chemists, while Follin and Bell [8] first applied a synthetic zeolite
for the collection and separation of ammonia from urine in 1917. Another
German Chemists Gans [9] had far reaching applications in mind even at thai
time, for example the recovery of gold from seawater. Perhaps he was the first
person in Germany who used the ion exchanger (processed natural /.eoliic) to
an industrial scale based on scientific understanding and technological
maturity. Therieafter a lot of scientific work was done on natural, processed and
synthetic inorganic materials for their ion exchange properties.
A spectacular evolution began in 1935 with the discovery by two
English Chemists, Adams and Holmes [10], that crushed phonograph records
exhibit ion exchange properties. Adams and Holmes synthesized organic ion
exchangers, called ion exchange resins. No sciendsts could then neglect ion
exchange phenomenon. These new resins were developed and improved by the
former I.G. Farbenindustrie in Germany and after World War II chiefly by
companies in the United States and England. However it took nearly 85 years
for the ion exchange phenomenon to be fiilly recognized in chemistry since its
scientific finding and understanding by Thomson and Way. The water
purification business was started in Japan in 1915 when a prominent
industrialist M. Masunari imported the patents of Cans and his group. Later on
the use of copolymer type ion exchangers such as Amberlite resins was started
in U.S.A. Although, at first the ion exchangers were mostly used for water
softening but soon they were widely employed in many other fields such as
analysis and preparative works. Their use gave analysts new materials that not
only met the requirements of modem laboratories but also led to the solution of
previously insolvable problems. Thus, ion exchange process has been
established as an analytical tool in laboratories and industries. An interest in
ion exchange operations in industries is increasing day-by-day as their field of
applications is expanding and is extremely valuable supplement to other
procedures such as filtration, distillation and adsorption. All over the world,
numerous plants are in operation, accomplishing tasks that range from the
recovery of metals from industrial wastes to the separation of rare earths, and
from catalysis of organic reactions to decontamination of water in cooling
systems of nuclear reactors.
The constant increase in the number of publications may be taken as the
best evidence for the spreading interest in ion exchange and for the hopes and
expectations that accompany its future development.
Just as applications of the organic resins are limited by breakdown in
aqueous systems at high temperatures and in the presence of high ionizing
radiation doses; for these reasons there had been a resurgence of interest in
inorganic ion exchanger in the 1950s. One of the possible ways of solving these
problems involved replacing the organic skeleton of the ion exchanger by the
inorganic skeleton. Pioneering work was carried out in this field by the
research team at the Oak Ridge National University by Kraus, and by the
English team lead by Amphlett. Potentially suitable ion exchange sorbents that
were studied included not only the oxides, hydrated oxides and insoluble salts
of polyvalent elements, but also the salts of heteropolyacids, hexacyanoferrates,
aluminosilicates and zeolite.
Further extensive research and study of inorganic ion-exchange sorbents
were carried out in the 1960s and 1980s. Research led from the original
amorphous type of ion-exchange sorbents to the study of crystalline ion-
exchange materials. Clearfield and co-workers made great contributions in this
area. In the last two decades, intensive research has continued on the synthesis
of a number of new organo-inorganic materials that have excellent properties.
Interest in the industrial use of inorganic and especially these organo-inorganic
ion exchange sorbents has also increased.
From a contemporary point of view, the development of ion-exchangers
and sorbents can be divided into several periods. Table 1.3 summarizes the
various stages of the development of ion-exchangers and sorbents.
Table 1.3: Stages of development of ion exchangers and sorbents.
Period
Up to 1850
1850-1905
1905-1935
1935-1940
1940-todate
Recently
Development
First experimental observations and information. The principle of
ion exchange had not yet been discovered.
Discovery of the principles of ion exchange and the first
experiments in the technical utilization of ion exchangers.
Use of inorganic ion exchange sorbents and modified natural
organic materials.
Rapid development of organic materials. Inorganic ion-exchange
sorbents were almost completely eliminated from all applications.
Continued rapid development of artificial organic ion exchangers
and by a renaissance in inorganic ion exchange sorbents and their
practical application.
The latest development in this discipline has been carried out with
the conversion of inorganic ion exchange materials into hybrid
(organo-inorganic) ion exchangers by incorporating organic
polymers.
Many natural and synthetic substances are capable of ion exchange. For
technical purpose, however only those substances that have adequate
mechanical and chemical properties are suitable. These materials may be
broadly classified as 'organic ion exchangers' and 'inorganic ion exchangers'
depending on the nature of matrix of which it is made up. These materials are
usually insoluble solid substances (large molecular polyelectrolytes) having
porous structure, which can take up ions of positive or negative charge from an
electrolyte solution and release other ions of like charge into the solution in an
equivalent amount. According to the charge of the exchangeable ions the
materials may either be a 'cation exchanger' (consist of a matrix carrying a
negative charge) or an 'anion exchanger' (consists of matrix carrying a positive
charge). The ions opposite to the charge of the matrix are called counter ions. A
material capable of exchanging both the cations and anions are termed as
'amphoteric ion exchanger'. Some liquid ion exchangers are also known.
The real utility of an ion-exchanger depends largely on its ion-exchange
characteristics. Ion exchange capacity, concentration and elution behaviour, pH
titration and distribution behaviour are some of the properties that constitute
the ion-exchange characteristics of a material. The ion exchange capacity
depends on two factors: [1] hydrated ionic radii and [2] selectivity. As the
hydrated ionic radius increases the ion-exchange capacity decreases because
the exchange now becomes more difficult. The selectivity of an ion exchanger
is affected by the nature of its functional group and but the degree of its cross-
linking. Ion exchangers containing groups that are capable of complex
11
formation with some particular ion will adsorb these ions more strongly. Iflhc
degree of cross-linking increases the exchanger becomes more selective in its
behaviour towards ions of different sizes. An increase in cross-linking also
decreases the swelling of the exchanger. The elution of H" ions from a column
depends on the concentration of the eluant. An optimum concentration of the
eluant necessary for a maximum elution of H^ ions depends upon the nature of
the ionogenic groups present in the exchanger, which in turn, depends upon the
pKa values of the acids used in it preparation. The efficiency of an ion
exchanger depends on the following fundamental properties of the materials.
• Equivalence of exchange.
• Donan exclusion-the ability of the resin to exclude ions but not the
undissociated substances, in general.
• Selectivity or affinity preferences of the exchanger for one ion relative
to another, including cases in which the differing affinities the ions are
modified by the use of complexing or chelating agents.
• Screening effect - the inability of very large ions or polymers to be
adsorbed to an appreciable extent.
• Differences in migration rate of adsorbent substances down a column
primarily a reflection of differences in affinity.
• Ionic mobility restricted to the exchangeable ions and counter ions only.
• Miscellaneous - swelling, surface area and other mechanical properties.
12
The stability of the ion exchanger is affected by their synthesis. The ion
exchange stability becomes especially evident in change of volume exchange
capacit}', the loss in ionogenic groups, swelling changes, in the formation of
new groups (especially weakly acidic) or in the destruction of the resin
skeleton] to various degrees. Chemical stability of synthetic ion exchangers
plays an important role in their analytical applications. Organic ion-exchangers
are usually stable in a wide pH range, while inorganic materials different
widely in this respect. The insoluble salts of polyvalent metals are highly stable
even in very concentrated acids. The thermal stability of ion exchangers
depends on the type of resin skeleton, its degree of cross-linking, and the type
of ionogenic group and their counter ions, fhe polymer materials of organic
resins breakdown at elevated temperature, with a concomitant decrease in their
exchange capacity. In contrast, inorganic sorbents are very stable at elevated
temperatures. Due to the swelling ability of the ion exchangers there is no
substantial difference between the degradation of dr) or swollen sorbent. It is
generally believed that inorganic ion exchangers are resistant to radiation.
Organic resins are very sensitive to exposure to high radiation doses, which
cause significant changes in their capacity and selectivity. Organic ion
exchangers are highly mechanically stable and can be prepared with defined
grain size, are resistant to abrasion, and are thus useful for use in packed
columns. In contrast, inorganic ion exchange sorbents exhibit poor
hydrodynamic properties and are difficult to prepare in the form of particles
with an acceptable particle size distribution.
13
ORGANIC ION EXCHANGERS
Organic ion-exchangers, commonly known as ion-exchange resins', are
know for their uniformity, chemical stability and high mechanical strength.
Organic ion-exchange resins consist of an elastic three-dimensional network of
hydrocarbon chains, which carry fixed ionic groups. The charge of the groups
is balanced by mobile counter ions. The resins are cross-linked
polyelectrolytes. They are insoluble, but can swell to a limited degree.
The ion-exchange behaviour of the resins depends chiefly on the nature
of the fixed ionic groups. Organic ion-exchangers may be natural or synthetic.
Sulphonated coal is an example of natural organic ion-exchanger. Synthetic
organic ion-exchange resins are superior to other materials because of their
high chemical stability, high mechanical stability, high ion-exchange rates,
high ion-exchange capacity and versatility. The most important synthetic
organic resins are copolymer product of styrene and divinyl benzene.
Organic ion-exchanger may be cation exchanger and anion-exchange.
Cation exchangers are further divided into strong acid cation exchanger and
weak acid cation exchanger; and anion exchangers are fiirther divided into
strong base anion-exchange resins and weak base anion exchange resins.
Although organic resins have wide application in analytical chemistry
because of their high stability in wide range of pH, reproducibility in results,
the main drawback has been their unstability under conditions of high radiation
at elevated temperature. This was the reason why an interest in the synthesis
14
and ion-exchange properties of inorganic ion-exchange materials was
developed.
INORGANIC ION-EXCHANGERS
The term 'inorganic ion-exchangers' is used in the title of monograph by
Amphlett, which describes the rapid development of these materials and their
applications in the 1950s and 1960s. The advent of nuclear technology initialed
a search for ion exchange materials that would remain stable above 150°C and
in high radiation fields. Inorganic ion exchangers possess these properties
retaining their i.e.c. and selectivities. They exhibit higher selectivities and
separation factors than their organic counterparts and hence have good
applications in the treatment of industrial and radioactive wastes, and
processing of radioisotopes in nuclear technology. Further researches have
shown that they have applications in the detection and separation of metal ions
under ordinary conditions also. They have been found useful in the preparation
of ion selective electrodes and as packing materials in ion chromatography.
Analysis of rocks, minerals, alloys and pharmaceuticals products have also
been made using these materials. Zirconium phosphate has been reported to be
useftil as adsorbent in the portable artificial kidney devices.
As the literature show that inorganic ion exchangers have become an
established class of materials of great analytical importance. At present we
have enormous literature available to the ion exchanger practitioner on the use
of inorganic ion-exchangers. These exchangers excluding, zeolite, which are
already heavily used, will find more use in the twenty first century. Since last
15
decades have been a great upsurge in the researches of inorganic ion exchange
materials, the main emphasis being given on the synthesis and characterization
of chemically stable materials and reproducible in ion-exchange behaviour.
Almost half a century of research on inorganic ion-exchange materials and
their great development in 1960s and 1970s is naturally reflected in the number
of monographs and reviews dealing with this subject. Books and monograph
necessarily provide a long-term picture of the given field, while reviews give
new information on the state of the art in a much shorter time interval.
Important advances in this field have been reviewed by a number of workers at
various stages of its development like Amphlett [11,12], Fuller [13|. Vcscly
and Pekarek [14, 15], Clearfild et al. [16, 17], Abe et al. [18, 19], Alberli ct al.
[20], Qureshi et al. [21, 22], Marinsky [23], Varshney et al. [24, 25], Ivanov ct
al. [26] and Terres-Rojas et al. [27]. Dyer has dealt with the theories involved
in zeolite molecular sieves [28-30], which have a direct relevance to llic
principle underlying the inorganic ion exchangers.
Pekarek, [14, 15] classified the inorganic ion exchangers into six broad
categories according to their chemical nature and structure. They are as
follows:
1. Insoluble acid slats of polyvalent metals.
2. Hydrous oxides of polyvalent metals.
3. Salts of heteropolyacids.
4. Insoluble hexacyanoferrates (II)
16
5. Synthetic aluminosilicates.
6. Miscellaneous inorganic exchangers e.g. mercarbide salts and potassium
polyphophates.
Clearfield [17], however, gave an expanded form of classification of
these compounds, indicating their 14 types show in Table 1.4.
Most of these materials possess the following qualities to be practically
useful.
1. They are virtually insoluble with in a reasonably wide range of pH.
2. They have appreciably good ion exchange capacity.
3. They show rapid sorption and elution behaviour.
4. They show resistance to attrition.
5. It is always easy to prepare them so that the minor changes in the
method or material used for their preparation do not cause major
changes in their performance.
6. They have high selectivity for certain metal ions.
Insoluble polybasic acid salts of polyvalent metals have shown a great
promise in preparative reproducibility, ion exchange behaviour, and both
chemical and physical behaviour. Many metals such as aluminum, antimon).
bismuth, cerium, cobalt, iron, lead, niobium, tin, tantalum, titanium, thorium,
tungsten, uranium and zirconium have been used for the preparation of ion
17
Table 1.4: Principal classes of inorganic ion-exchangers.
S.No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Type
Smectic clays
Zeolites
Substituted
aluminium
phosphates
Hydrous
oxides
Group IV
phosphates
Other
phosphates
Condensed
phosphates
Heteropoly
acid salts
Ferrocyanides
Titanates
Apatites
Anion
exchangers
Miscellaneous
types
Fast ion
conductors
Example
Montmorillonites M"*x/„ [AI4.X Mgx] (Sig)02o(OH)4
Na,(A102)x(Si02)y.zH20
Silico aluminophosphates, Metal-substituted
aluminophosphates
(M"\Al,.x02)(P02)(OH)2x/„
(a) Si02.xH20, Zr02.xH20
(b) [H30]2 Sb206, Polyantimonic acid
Zr(HP04)2. H2O, Sn(HP04)2.H20
Uranium phosphates, vanadium phosphates, antimony
phosphates
NaPOj
MnxY,2O40.H2O
[M=H\ Na"NH4"; X = P, As, Si, B; Y=Mo, W]
M4/„"^Fe[CN]6
[M=Ag^, Zn^\ Cu " , Zn"**, n=ion charge]
Na2Ti„02„., (n=2-10]
Ca,o., H« (P04)6 (0H)2.,
Hydrolalcitc
Mg6Al2lOH]„C03.4H20
Alkalinc-carth sulphates polyvanadates, sulphides
P-alumina. Na,., AInOi7-x/2
NASICOM. Nai.^Zr.SixP,., 0,2
Exchange
capacity [meq/ gj
0.5-1.5
3-7
Depend upon
value of x
1-2
1-5
4-8
-
8
-
1.1-6.1
2-9
Cation and anion
exchange
An ion-exchange
2-4
-
1.5-3
2-7
exchange materials. Also a large number of anionic species such as phosphate,
tungstate, molybdate, arsenate, antimonate, silicate, telluride, ferrocyanide,
vanadate, arsenophosphate, arsenotungstate, arsenomolybdate, arsenosilicate,
arsenovanadate, phosphomolybdate, phsophosilicate, phosphovanadate,
molybdosilicate and vanadosilicate etc. have been used to prepare inorganic ion
exchangers. The majority of work carried out on zirconium, titanium, tin,
niobium and tantalum.
COMPOSITE MATERIALS
Two or more materials are combined together to produce a new
materials that may posses much better properties than any one of the
constituent materials. The new materials are called as composite material. For
example wool is a natural composite, which consists of long cellulose fibers
held together by amorphous lignin. Some artificial or synthetic composite
materials are cement, inorganic fillers in plastics, or organic coatings on the
surface of metals etc. There are three types of composite materials:
(a) Agglomerated materials: In this process the particles arc condensed
together to form an integral mass and are known as agglomerated
composite materials (e.g. cement concrete).
(b) Laminated materials or laminates: The materials which arc produced by
bonding two or more layers of different materials completely to each
other are known as laminated materials or laminates (tufnol).
(c) Reinforced materials: The materials that are produced by combining
suitable material to provide additional strength, which does not exist in a
single material are known as reinforced materials (e.g. nylon reinforced
rubbers, fiber reinforced plastics etc.).
The word 'composite' is used in the technical sense to describe a
product that arises from the incorporation of some basic structural material into
a second substance the matrix which is incorporated either in form of particles,
whiskers, fibers or a mesh. The main characteristics sought in an additive that
in turn gets conferred on the composite, are elastic rigidity, tensile and fatigue
strength, hardness and appropriate electrical and magnetic properties. Thus a
polymer composite may be defined as a combination of a polymer with one or
more other materials to produce a new material to avail advantages of desirable
properties of each component. Hence, in composite materials, the interface
between two different materials is very important feature of their durability or
mechanical properties. In other words, the concept of these composite materials
is 'paste together' to form a material with improved properties.
Composite materials formed by the combination of inorganic materials
and organic polymers are attractive for the purpose of creating high
performance or high functional polymeric materials. Of particular interest is the
molecular level combination of two different components that may lead to new
composite materials that are expected to provide many possibilities, termed as
"Organic-inorganic hybrid materials". These hybrid materials usually show
properties intermediate between those of plastics and glasses (ceramics).
20
Accordingly, hybrids can be used to modify organic polymer material or to
modify inorganic glassy materials. In addition to these characteristics the
hybrid materials can be considered as new composite materials that exhibit
very different properties from their original components (organic polymers and
inorganic materials). In other words, hybrid materials should be considered as
next generation composite materials that will encompass a wide variety of
applications.
ORGANIC - INORGANIC HYBRID ION-EXCHANGERS
The conversion of inorganic ion exchange materials into hybrid ion
exchangers is the latest development in this discipline. The preparation of
hybrid ion exchangers is carried out with the binding of organic polymer i.e.
polyaniline, polyacrylonitrile, polyacrylic acid, polymethylmethacrylate,
polystyrene, pectin etc. These polymer based hybrid ion-exchange materials
show an improvement in a number of its properties. One of them is its
granulometric properties that makes it more suitable for the application in
column operations. The binding of organic polymer also introduces better
mechanical properties in the end product i.e. hybrid ion exchange materials.
Hybrid ion exchangers can be prepared as three-dimensional porous materials
in which layers are cross linked or as layered compounds containing sulphonic
acid, carboxylic acid or amino groups. Some hybrid ion-exchangers prepared
so far are pyridinium-tungstoarsenate [31], zirconium (IV)
sulphosalicyclophosphate [32, 33], styrene supported zirconium phosphate
[34], polyaniline tin (IV) phosphate [35].
FIBROUS ION-EXCHANGERS
Fibrous ion-exchangers have been of recent origin and these materials
have drawn the attention of researchers and experimentalist as they exhibii a
high efficiency in the process of sorption from gaseous and liquid media.
Fibrous ion-exchange materials have great advantage of having capability lor
obtaining in different forms such as conveyer belts, non-woven materials,
staples, nets and cloths etc. This may open new and novel possibilities of using
these materials in environmental analysis as shown in Fig. 1.1.
Fibrous ion-exchangers consist of monofilaments of uniform si/c
ranging in diameter between 5-50|im. This predetermines short diffusion path
of sorbates in a sorbent and high rate of sorption, which can be about hundred
times higher than that of granular resins, which have particle ranging in
diameter 0.25-Ifim, normally used in such processes. Thus, they arc more
useful in large-scale processes. These ion exchangers have extremely high
osmotic stability, which allow them to be used in conditions of multiple
wetting and drying occurring at cyclic sorption process or regeneration process
in air purification. Fibrous ion-exchanger, open new alternatives in ion-
exchange processes. The literature study shows that most of the researches on
ion-exchange fibre have been done at USSR and Japan, thus these arc Ihc main
centres of origin.
Number of monographs [36-38] review papers [39-40] and patents arc
described which deal with the preparation methods, technologies properties and
(c)
Kegeneratlor ba£h
lEF
. . r * - ^
Fig.1.1 Variants of application of ion-exchange fibres (lEF) in liquid and gaseous processes.
(a) Ion-exchange columns with different filling (i) Staple pulp (ii) Parallel threads (iii) Layers of fibrous material
(b) Coveyer belt made of ion-exchange fibres (Process with continuous regeneration).
(c) Mats made of lEF in the river or sea stream. (d) Dragging nets made of lEF. (c) Chemical air filters with IFF. (0 Gas mask or respirator filled with lEF material.
23
possible areas of applications of fibrous ion-exchangers. Ihe tentative
production of different fibrous ion-exchangers (VION®) has been organized in
the USSR.
Similar products are also produced in Japan [40,41]. Recently, research
has been carried out to develop preparation methods for fibrous ion-exchangers
of different types and identification of different fields such as air purification
from acidic and alkaline impurities [36,42], water purification, preparative
chromatography etc. at the Institute of Byelorussian Academy of Sciences
Minsk, USSR. Japanese and Western authors [43-45] have done a lot of work
related to water purification, extraction of uranium, gold and other useful
substances fi'om water. Here, various applications of fibrous ion-exchangers
make it possible to employ other conventional column methods.
Fibrous ion-exchangers have the registered trademark "Fiban®" [46].
Fiban [47] is a strong acid cation exchanger. It is prepared by sulphonalion of
styrene divinylbenzene copolymer grafted on to polypropylene fibre. Fiban A-1
[48] is a strong base fibre, is a product of chloromethylation and subsequent
amination of the same grafted copolymer with trimethylamine. Fiban K-1 and
A-1 ionexchangers are analogues of common granular ion-exchange resins and
can be used for the same purpose. The Fiban AK-22, is a weak base polyacrylic
fibre, is a complex forming polyampholyte containing imidazoline and
carboxyl groups [49].
Two families of Fiban fibres are developed. One of them is prepared by
grafting of polystyrene onto polypropylene fibres. It was carried out al room
24
temperature by use of styrene solutions in organic solvents by means ol
generation of radicals in the polypropylene matrix initiated by lOOrad/s
radiation. In other cases, about 2% vinyl benzene was added to styrene. I'ig. 1.2
shows the scheme for the preparation of the family of fibrous Fiban ion-
exchangers. The exchange capacity of these ion-exchangers can be varied
changing the quantity of polystyrene grafted onto polypropylene fibres and
degree of polymer analogous transformations. Under several condition.s
grafting degree can be raised to 600% (6 weight parts of polystyrene per one
weight part of polypropylene), the sulphation degree to 1, amination degree to
1.2, (ftinctional groups per benzene nucleus). The exchange capacity of ihcsc
ion-exchangers can reach up to 4.5meq/g. The exchange capacity of anion
exchangers with imidazoline groups can be up to 11 meg/g. The problem in
synthesis of ion exchanger fibres is compromisingly high exchange capacit\
and their mechanical properties (tensile strength and elasticity). An increase in
ion-exchange capacity leads to decrease in mechanical and textile
characteristics. The swelling of fibres should be maintained within acceptable
limits. The swelling properties of fibrous ion-exchangers can be varied b\
changing the polystyrene grafting degree, the divinylbenzene content, the
number of ftinctional groups, the grafting conditions and treatment of fibres
Swelling of fibrous ion-exchangers qualitatively depends on the ionic form and
the way of swelling resembles with conventional granular ion-exchangers. The
preparation of ion-exchangers of maximum capacity serves no practical
25
HjC—CH
CHo
H2C=CH H2C=CH
c o •c .2 •5 (d
fc 51
Polypropylene - graft [Styrene-DVB Copolymer]
HjS04.AT
'
1. CHjOCHjCl; SnCU; ZnCli, AT
2. (CH3)3N.AT
r .
FIB AN K-1
'
FIB AN A-1
1. CHsOCHjCI; SnCU; ZnCli, AT
2. NaOH. AT 3. HNO3, AT
' FIBAN K-J.
R coou o o 0-0
S03H CH2-N"*"(CH3)3Cr COOH COOH
Fig.1.2 A technological scheme for preparation of Fiban ion exchangers.
26
purpose due lo unfavourable mechanical, osmotic properties, as well as
swelling ratio.
Ion-exchange fibres open new technological possibilities for metal ions
recovery, purification of water and treatment of water in natural reservoirs. Ion
exchange fibres when used for purification of water and gases may undergo
osmotic shocks or may be exposed to aggressive media. Fibrous ion-
exchangers can be used to make fabrics under some mechanical characteristics.
Fibrous ion exchangers are uniform in diameter as compared to commercial
granular ion-exchange resins. For weaving fabrics, the strength of ion-
exchange fibres is kept high. They can withstand multiple bends without
destruction. The ion-exchange capacity is not affected when they undergo
various osmotic shocks induced by frequent changes in swelling. The structure
of fibres depends on the method of preparation of starting graft copolymer. It
may be more or less porous in nature and yield ion-exchanger of greater or
lesser mechanical and osmotic strength. Ion exchange fibres are produced by
introducing, through radiation initiated by graft polymerization, ion-exchange
groups into the sheath of each composite fibre the core and the sheath of which
is composed of different kinds of high polymer components. Exposing fibres
with a core/sheath structure to an ionizing radiation and then grafting a
polymerizable monomer to the fibres produce separation functional fibres. The
separation ftinctional fibres and ion-exchange fibres arc useful in purification
of pure water in electric power, nuclear, electronic and pharmaceutical
industries and demineralization of high- salt content solutions in production of
27
food and chemicals. The fibers are also useful in removing harmful gases as
well as odorous components such as ammonia [50].
The preparation of acrylic grafted polypropylene fibres improves
indyeability of polypropylene fibre through high-energy radiation grafting
technique [51]. It evaluates the role, actual and potential of high-energy
electron beam irradiation of polypropylene fibres for grafting with aqueous
solutions of two acrylic monomers in the presence of peroxide catalyst. The
most effective combination depends on a particular molar ratio of each
monomer, which give a synergetic influence on graft yield.
Fiban K-1 and Fiban A-1 fibres have a chemically inert matrix,
polypropylene. The chemical stability of Fiban K-1 and Fiban A-1 fibres
towards acids, bases, oxidants and majority of solvents under ordinary
conditions is similar to that of common styrene-divinylbenzene ion-exchangers.
The thermal stability of ion exchange fibres is determined by properties of
polypropylene-polystyrene binding nodes. Besides, various effects of anion
exchangers, it has been found fibrous ion-exchangers [52] that at 160°C an
endothermal peak appears in DTA curve which provide an evidence for the
melting of polypropylene matrix crystallites. In addition, at I85-I96°C a sharp
increase in heat release is observed. The studies of ion-exchange capacity and
infra-red spectra showed that above affects can also be explained by the
overlapping of an endothermal process and decomposition of functional groups
of anion exchange fibres upon exothermal oxidative polypropylene destruction.
Thus, Fiban A-1 Fiban K-1 can be applied under similar conditions to granular
28
styrene divinylbenzene ion-exchangers. The osmotic stability of fibrous ion-
exchangers based on polypropylene fibres appeared to be very high. Ihcy
undergo thousands of swelling-contraction cycles upon alternate treatment with
acids and base, as well as drying and wetting while the fibrous ion-exchangers
with polyethylene fibres [53] shows a more homogenous composition of
functional groups and a higher elasticity.
Fibrous ion-exchangers [54, 55] obtained in the form of sheet have high
permeability to air and water. Watanabe [56] described a method for
manufacturing partially heat-bonding ion-exchange fibres and fibre containing
components (A) having melting point lower than the ion-exchange fibres and
or components having melting point higher than the A. Thus, a piece of paper
(basis wt.lOO/gm) prepared from 50:50 mixture of multicore ion-exchange
fibre (diameter 40\im, length 0.5mm) and cellulose fibre was pressed at 5
kg/cm^ dried at 90°, laminated with a web (basis wt., 30g/m^) of component
hot-melt adhesive fibre (B), sandwiched between steel nets, and heated at
175°C for 3 min to form a sheet showing tensile strength 4.1 kg/15 mm
(longitudinal) and 4.2 kg/ 15 mm (transverse) tear strength (3.8 kg /cm^) and air
permeation 4.9cm /cm -S. The Ion-exchange fibre sheet in the form of tobacco
smoke filter material [57, 58] prepared by sulphonating polymer fibres,
selectively remove carcinogenic and mutagenic substances from cigarette
smoke, without affecting flavour and aroma. Thus, a compound containing
polyst}Tene (9003-53-6) 40 and polypropylene (9003-07-0) 10 parts enclosing
polypropylene 50 parts were spun at 270°C to yield fibre (42 denier, 42
29
filament). The fibres were cut into 1 mm segments. The cut fibres were soaked
in a solution containing H2SO4 22, nitrobenzene 104 and paraformaldehyde 0.3
parts. The fibres were allowed to with stand at room temperature for 6 hours,
washed with water and then ethyl alcohol and dried. The dried fibres were
soaked in H2SO4 at 90°C for 24 hours washed and dried. The fibres were H-
type, sulphonic acid-containing strongly acidic cation exchangers, (ion-
exchange capacity 3.0p.gNa/g, water content 12.3%). The fibres were fibrilized
in a. blender, mixed with an equal amount of polyethylene pulp, and made into
sheet. The sheet and poly (ethylene terephthalate) were layered and made into
cigarette filter tips. The cigarette filter tips give more tars than a conventional
one, and gave high organoleptic test scores. Ion-exchange fibres and their
fabrics have been introduced and their main properties such as microsmic
surface appearance, physical properties, absorption capacity, regeneration and
dust holding properties have been studied comprehensively. Using non-woven
fabrics as purifying material, a new type harmfial gas purifier has been
developed.
Fibrous ion-exchangers can be used for many hydro metallurgical
processes and are accompanied by air pollution with volatile acid anhydrides
and aerosols. The various properties of ion-exchangers give an idea for their
use in air purification. Various publications [59-67] describe the sorption of
SO2, CO2, NH3, HCl by ion-exchange resin The high sorptive capacity with
positive effect of humidity is responsible for the development of new air
purification technologies. These technologies are related or deal with large
30
volume of purified air. Even smallest scale processes require treatment of
thousands of cubic meter of air per hour. It means that flow rates in them must
be high which need high sorption rates.
Fibrous ion-exchange materials in the form of cloth or non-woven belt
can be used for removal of impurities from gas flows. They contain filament
with thickness below 50 microns. It has been shovm that rate of sorption is one
or two orders of magnitude higher than that of industrially produced resins of
similar chemical structure [68]. The materials are elastic in nature to some
degree and have outstanding osmotic stability [69]. The number of studies
proves thy advantages of various applications of fibrous ion-exchangers in
gaseous processes [70, 71].
Fiban A-1 and Fiban AK-22 were tested for removal of acidic impurities
such as CO2, H2S, SO2 and vapour and aerosols of inorganic and some
carboxylic acids from air. Fiban K-I was tested for removal of ammonia from
air [72, 73]. Strong base ion-exchange fibre. (Fiban A-1) can be used for
sorption of any acidic impurities but it is most rational to apply them only to
sorption of weak acids or substances forming acids in humid media since
regeneration in this case is easier than that for strong acids. Practically,
important cases are HjS. CO2, HCN, CI2. Alkaline solutions are used for
regeneration of anion exchanger. Weak acidic ion exchange fibres (lEF) like
Fiban AK-22 can be used for sorbing strong acids. Alkaline impurities can be
efficiently sorbed by carboxylic (Fiban K-4) or sulphonic (Fiban K-1) type of
lEF.
31
Fibrous ion-exchangers are used to prepare deodorizing cloth by
weaving ion-exchanger grafted fibres with either natural or artificial fibres
[74]. The cloth is used for manufacturing bedding and clothing. Polyester fibres
were irradiated with 20Mrad. electron in nitrogen and soaked in a solution
containing hydroxystyrene monomer and isoprene to give grafted polymers,
which were aminoquatemized to form anionic fibres. Polyester fibers were
irradiated with 20Mrad. electrons in nitrogen soaked in acrylate solution to give
grafted polymers, which were treated with NaOH solution to give cationic
fibres. Cloths were prepared using these fibres.
Fibrous ion-exchangers are useftil in metallurgical applications. They
are used for recovery of gold in the presence of cyanide solutions from aqueous
solutions by hydrogen reduction in thiosulfate solution. Kotze [75,76]
synthesized fibrous ion-exchangers using propylene staple as cheap, stable and
robust base. Styrene was copolymerized onto propylene fibres. Various anionic
groups were fixed on this material to find the most effective ion-exchanger for
the selective recovery of gold in the presence of other metal cyanide. Belfer
[77] described the gold cyanide absorption by new fibrous ion-exchanger
prepared by tiie amination of sulfochlorinated polyethylene. Deventer [78]
deals with the competitive adsorption of organic compounds and gold cyanide
onto ion-exchange fibre and membrane. Loadings of organic compounds were
measured on gold equilibrated adsorbents and compared to loadings on virigin
adsorbents. Fibrous ion-exchangers were used for recovery of high purity zinc
oxide from steel making dust [79]. These ion-exchangers are also used for
recovery of non-ferrous metals [80] like Cu and Ni were removed from
simulated and real mine water.
Fibrous ion-exchangers are used for solidification of radioactive waste
[81] manufacture of fabrics capable of removing ionic substances [82], removal
of chromium trioxide [83] from waste gases, removal of [84] mercury from
waste water with 84.2-100% efficiency. Removal of heavy metal ions from
water [85] like Cu, Pd, Zn, Fe, Co, Ni, Ag, Cr and Mn. PAN-PEA and carbon
fibres were used for their removal from waste water, removal of toxic gases
[86], cleaning of environment [87] and removal of arsenic from chloride
medium [88].
Fibrous ion-exchangers act as prospective sorbents for the separation of
rare earths and aerosols [89-91]. They have high efficiency for separation of
heavy metal ions from aqueous solutions [92, 93]. Fiban AK-22 [94] for Cu^ ,
Cd^ , Ni^^ and Co^^ was studied as a function of pH and showed that the ion-
exchanger can be used for quantitative analysis of Cu, Ni and Co in mixture as
well as for their preparative separations by selective elutions from
chromatographic column. Cu-Ni, Ni-Co, Cu Zn, Zn-Pd and Cu-Ni-Co mixtures
were separated by elution with stepwise change of the pll.
Fibrous ion-exchangers can be used in form filters. Filters are made up
of ion-exchange fibres manufactured by radiation graft polymerization, for
example polyolefins. Activated carbon is optionally used along with ion-
exchange fibres. The air filters are used for removal of hazardous gases,
malodorous gases, or fine particles from air in automobiles, gas cleaning filter
33
holders for accurate determination of gases. Chemical filters are prepared for
ultrapurification of clean rooms [95]. The non-woven filtering materials
[96,97] are used for removal of harmful compounds like nitrites, nitrates, heavy
metals, surfactants, herbicides, oils, free CI etc. from potable water. Non-
woven fabric containing ion-exchange fibres for filtration of gas is studied [98].
The filters [99] consist of ion-exchange fibers of chloromethyl styrene
graft polymer quaternary ammonium compounds and 4-vinyl pyridine graft
polymer quaternary ammonium compounds. The filters rapidly and certainly
collected micro-organism floating in air and are suitable for use in air-
conditioning systems. Filtering material comprise ion-exchange sheets and
electrically polarized synthetic fibre sheet with separator for air filters [100].
In 1998, Clemente [101] described a process which dealt with the
transformation of residuals and excess of vegetable, herbaceous plants, quickly
renewed vegetable in a fibrous material having high content of cellulose, and
paper characteristics and directly suitable for the production of paper and board
without using polluting and toxic chemical products.
Ergozhin [102] synthesized fibrous ion-exchanger by treating poly
acr>ionilrilc fibre waste with [1: 17] H2S04-Hydroxylamine sulphate mixture
and simultaneous neutralization with Na2C03 or alkali during heating at 40-
50°C. Fibrous ion exchangers were prepared to obtain good sorption properties.
In this method, carboxylated acrylic fibres were modified partially with
epichlorohydrin polyethylene-polyamine adduct, PAE [103]. The ion-exchange
capacity of PAE modified fibres with respect to HCI was -53% of the
theoretical value. The capacity increased from 2.1 lo 3.6mmo/g with increasing
modification temperature from 20-100°C and from 2.7-4. Immol/g with
increasing COOH group content from 0.7 lo 2.5mmo;/g. The good sorption
properties were obtained when the fibres were dried at 20°C.
Kinetic Characteristics of process of electrodialysis with different
fibrous ion-exchangers in desalination chamber [104] are studied. Kinetics of
preparation of biologically active fibres with anesthetic activity is described
[105].
Zosina [106, 107] prepared fibrous porous composites with good sound
proofing properties from polyvinyl alcohol binder and HCHO, in the presence
of mineral catalyst, by filling l-3mm polyacrylonitrile fibres waste from fur
substitute manufactured non-woven needle-punched fabrics from recycled
wool, polyamide fibres, acrylic ion-exchange fibres.
Borell [109] prepared fibrous ion-cxchangcrs by introducing basic
groups, for example, tertiar)'-aminc. tetra-hydropyrimidine, imidazoline,
quaternary ammonium groups onto cross-linked water insoluble,
polyacrylonitrile fibres. This fibre had ion-exchange capacity of 6.3mm/g.
Ivanova [110] prepared fibrous ion-cxchangcrs based on polyacrylonitrile
modified with sodium-alkyIsiloxanes.
Pushpa Bajaj synthesized acrylonitrile-acrylic acid copolymers f i l l .
112] and acrylic fibres [113-119] having high tenacity, spinning, chemical and
technical applications. Bajaj also studied the influence of spinning dope
activities and spin bath temperatures on the structural and physical properties
35
of acrylic fibres [120].
Zosina et al [121] studied the characteristics of modification of
polyacrylonitrile fibres by metal alkyl silanolate complexes. They synthesized
heat resistant ion-exchange fibres by base hydrolysis of as-spun
polyacrylonitrile fibres in the presence of Zn[AI-Zn, Fe(III)-Zn, Zr, Sn (IV)]-
Me Si [OH]20Na complexes. Most active complex was Fe (Ill)-Zn and least
active was Sn (IV) complex. Sorbents based on polyethylene Polyamine [PEA]
modified [PAN] polyacrylonitrile fibres [122] are used for concentrating Mo,
W, Va, Cr and As and for the extraction of these elements from natural and
waste water. PAN-PAE sorbents are weakly basic anion exchangers in OH and
cr forms.
Ion-exchange fibres based on polyvinyl alcohol polyacrylonitrile
containing COOH group [123] were used for absorption of insulin. Andreeva
[124] studied the absorption of Mo^\W^^V^^Cr^^ & As^^ on a fibrous
exchanger of polyacrylonitrile modified by polyethylene polyamine Cr ^
becomes strongly bonded to the exchanger.
Volf [125] prepared the selective ion-exchange fibres from
polyacrylonitrile and polyvinyl alcohol fibres for the sorption of precious
metals by modification with hydroxylamine in the presence of polyethylene-
polymine or by bonding the fibres pyrazole and mercaptobenzothiazole.
Yoshioka [126-132] first prepared a polystyrene based ion-exchange fibre by
using an islands-in-a-sea type composite fibre. It possesses large ion-exchange
capacity and a high mechanical strength. It was found that the resulting fibre
36
has two fundamental characteristics, ion-exchange rale for metal ion is very
high and the capacity of adsorbing the macromolcculc ionic substances is
accordingly large compared with ordinary ion-exchange resins Polystyrene
derivatives are used for water purification in nuclear plants. They act as
effective solid acid catalyst. Fibres articles are shaped like honey-comb.
Like Fiban VION® fibrous ion-exchange materials are also studied. All
the VION fibres are [133] acid resistant but undergo hydrolysis of nitrite
groups to carboxylic groups in alkaline solutions. Na2C03 solutions are
recommended for regeneration of ion-exchanging fibres.
Water vapour sorption by carboxyl group containing chemisorptive fibre
in different ionic forms of acrylic fibre Vion was studied. Preparation of Vion
chemisorptive fibres in concentrated hydrazine hydrate solution was discussed
[135].
VION® fibrous ion-exchanger materials can be used in the purification
of gases from acidic and basic impurities. It has confirmed by Barash et al.
[136-138]. They studied the effect of repeated generations on the properties of
Vion AN-I ion exchange fibres for the removal of the harmful emissions, for
example, HCI from gas- air and liquid media was studied, ilic ion exchange
capacity [lEC] of fibre was not affected by regeneration in 0.1 N acid and
alkali solutions but the ion- exchange capacity decreased to 92.1 and 78.8% by
repeated generation in 5N H2SO4 and IN HNO3 respectively. The lEC of fibres
increased when treated with 1.25 N NaOH at 90° due to the nitrile group
hydrolysis.
37
Polovikhina [139] studied the sorption of chloride, nitrate and sulphate
anions under static and dynamic conditions for fibrous anion exchanger- Vion
AS-1 containing pyridine groups and Vion AS-2 containing diphatic anion
groups. The sorption process is dependent on size of anion of fibrous sorbents.
The study of insoluble crystaUine acid salts of tetravalent metals has
facilitated the preparation of several new crystalline fibrous inorganic ion
exchangers. The first fibrous acid, salt of tetravalent metal was cerium (IV)
phosphate prepared by Alberti el al. [140,141]. A very interesting feature of
fibrous cerium phosphate is that it results in a flexible sheet similar to cellulose
paper [142]. Fibrous cerium (IV) phosphate shows at low loading, a maximum
uptake of Cs(I) alkali metals and for Ba(II) among the alkaline earths. On
increasing the loading a reversal in selectivity is observed. Support free fibrous
cerium (IV) phosphate sheets have already been used for chromatographic
separation of inorganic ions and are found to be selective for certain cations
such as Pb (II), Ag (I), T1(I) and K(I). Later on fibrous thorium phosphate [143,
144] titanium [145,146] and titanium arsenate were prepared or obtained.
Fibrous inorganic ion exchangers arc ver>' interesting because they can be used
in the preparation of inorganic ion exchange papers or thin layers suitable for
chromatographic cation separations. ITic inorganic papers of thorium
phosphate can be prepared easily and can be compared to those of cerium
phosphate as regards in chromatographic separation where reducing agents arc
often used as eluants or spot test reagents. They can also be utilized to prepare
38
ion-exchange membranes without a binder [147,148] with good electro
chemical behaviour [149].
Varshney et al. synthesized some new fibrous ion-exchangers [150-152]
with promising ion-exchange behaviour supported by some important
separations achieved practically. Further, because of the fibrous nature of these
materials new technological possibilities have emerged as they can be used in
different convenient forms for the abatement of environmental pollution.
The insoluble acid salts of tetravalent metals have been employed to
prepare inorganic ion-exchange membranes, which are interesting from both
fundamental and practical point of view. Owing to their high selectivity and
stability these membranes have applications as selective electrodes where
organic membranes fail. They can be successfully employed in fuel cells at
high temperatures or in concentrating the waste containing fission products.
From the above literature, and number of publications we conclude that
very less work have been done on fibrous ion-exchangers in regard of
production of ion-exchange fibres. The chemistry of processes involved have
not been studied thoroughly. Little studies have been reported on the properties
particularly, mechanical and textile properties. The problem in the synthesis of
fibrous ion exchangers have been compromisingly high ion-exchange capacity
and mechanical properties i.e., tensile strength and elasticity. Increase in ion-
exchange capacity leads to fall in their mechanical and tensile characteristics.
Number of investigations has been made regarding the method of
preparing fibrous ion-exchangers, which have large surface area per unit of
39
weight and can be used in an arbitrary form [153-155]. The following
indispensable conditions are kept in mind to prepare the ion- exchange fibres.
1. The material should be insoluble within a wide range of pH.
2. The ion-exchange capacity should be large enough to ensure practical
operation.
3. The mechanical strength should be sufficiently high.
4. The ionic group and basic polymer should be chemically stable.
The fibrous materials open new and novel possibilities in environmental
analysis for the separation or removal of harmful ionic impurities from aqueous
and gaseous media, it was thought worthwhile to investigate further the
possibility of synthesizing fibrous material, which may be good ion-exchangers
also. In view of this, efforts have been made in laboratories to obtain fibrous
ion-exchangers having inorganic matrices to make them of greater use for the
selective removal of ionic impurities at high temperature using strong
radiations.
The present study is concentrated on preparing the granules of fibrous
ion-exchange materials suitable for column use or preparing their membranes
useful for analytical separations. The following chapter summarizes the
synthesis and characterization of "Pectin based Cerium (IV) and Thorium (IV)
Phosphates".
40
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50
(^
CHAPTER 2
SYNTHESIS, CHARACTERIZATION AND THERAAAL BEHAVIOUR OF PECTIN BASED
CERIUM (IV) AND THORIUM (IV) PHOSPHATES AS NOVEL HYBRID FIBROUS
ION-EXCHANGERS
I ^
2.1 INTRODUCTION
Materials containing both organic and inorganic parts in their structure
are termed as organic-inorganic ion exchangers, generally known as hybrid ion
exchangers. These materials have attained an important status in analytical
chemistry in the recent past because of their improved ion exchange
characteristics as compared to both inorganic and organic ion exchangers. They
contain the polymeric species like polyacrylonitrile, polystyrene,
polyacrylamide, pectin etc. in their structure. These materials are expected to
have high radiation and temperature stability. Because of the reproducible
behaviour and ion exchange properties, their utility have been demonstrated for
the separation of various metal ions [1].
These materials have also shown fibrous nature as confirmed by SEM
studies. Fibrous ion exchangers open a new land of opportunities in industrial
and environmental applications as they can offer wide range of interesting
properties and can be obtained in different convenient forms such as cloth,
conveyor belts, nets etc.
Recently we have produced acrylonitrile based cerium (IV) phosphate
(ANCeP) [2], polyacrylonitrile based thorium (IV) phosphate (PANCeP) [3],
polystyrene thorium (IV) phosphate (PStThP) [4], acrylamide based thorium
(IV) phosphate (AAThP) [5] and acrylamide based cerium (IV) phosphate
(AACcP) (6), which have shown selectivity for Hg(II). Pb(II), Cd (II), Pb (II)
and Hg (II) respectively.
In continuation of such studies wc have synthesized pectin based cerium
(IV) phosphate (PcCeP) and pectin based thorium (IV) phosphate (PcThP),
which possess a fibrous structure. Following pages summarize the synthesis,
ion exchange characteristics and thermal behaviour of these new materials.
51
2.2 EXPERIMENTAL
2.2.1 Reagents and Chemicals
Ceric sulphate [Ce(S04)2.4H20], Thorium nitrate [Th(N03)4.5H20] and
pectin (Poly-D-galarturonic acid methyl ester), were obtained from CDH
(India) while phosphoric acid (H3PO4) was a Qualigens (India) product. All
other reagents and chemicals were of analytical reagent grade.
2.2.2 Instrumentation
pH measurements were performed using an Elico Model LI-10 pH
meter. X-ray diffraction studies were made on Bruker Analytical X-ray
diffractometer, model D8 advance and IR studies were carried out by the KBr
disc method using Perking Elmer FTIR spectrometer RX-I, SEM studies were
done with LEO 435 VP scanning electron microscope. For TGA/DTG, Perkin
Elmer, Pyric Diamond model was used. For elernental analysis, Heraeus Carlo
Erba-1108 analyzer was used.
2.2.3 Preparation of the reagent solutions
Solution of ceric sulphate and thorium nitrate were prepared in 0.5M
H2SO4 and IM HNO3 respectively and those of orthophosphoric acid and
pectin were prepared in double distilled water.
2.2.4 Synthesis of the ion-exchange materials
A number of sample of PcCeP and PcThP were prepared by adding one
volume of, 0.05M Ce(S04)2.4H20 (in case of PcCeP) and O.IM
Th(N03)4.5H20 (in case of PcThP) solutions in two volumes of (1:1) mixture
52
of, 6M H3PO4 (in case of PcCeP) and 2M H3PO4 (in case of PcThP) and pectin
(varying % age), dropwise with constant stirring using magnetic stirrer, at a
temperature of, 70±5°C (in case of PcCeP) and 90±5°C (in case of Pel hP). The
resulting slurry obtained under these conditions was stirred for 4h at this
temperature, filtered and then washed free of sulphate ions with demineralized
water (pH~4). Finally, the slurry of both PcCeP and PcThP were dried at room
temperature, resulting in a fibrous shiny sheets, which were cut into small
pieces and converted into H" form by treating with IM HNO3 for 24h with
occasional shaking and intermittently replacing the supernatant liquid with 1M
HNO3. The materials thus obtained were then washed with demineralized water
to remove the excess acid before drying finally at 45°C. The ion exchange
capacity of PcCeP and PcThP, were found to be maximum for sample PcCeP-2
(Table 2.1) and PcThP-11 (Table 2.2) respectively. These two samples were
selected for further studies.
2.2.5 Ion-Exchange Studies
2.2.5.1 Ion exchange capacity
The ion exchange capacity (i.e.c.) of the sample was determined as usual
by the column process taking 1 g of the material (H" -form) in a glass tube of
internal diameter ~1 cm, fitted with a glass wool at its bottom. 250 ml of 1 M
NaN03 was used as eluant, maintaining a very slow flow rate (-0.5 ml min').
The effluent was titrated against a standard alkali solution to determine the total
H*-ions released. The ion exchange capacity for Na^ ion and other metal ions
were determined for both PcCeP and PcThP. The results are summarized in
Table 2.3.
53
Table 2.1
Synthesis of various samples of pectin based cerium (IV) phosphate.
Sample Number
PcCeP-1
PcCeP-2
PcCeP-3
PcCeP-4
PcCeP-5
PcCeP-6
PcCeP-7
PcCeP-8
% Pectin added
0
1
2
3
5
10
11
12
Na ion exchange
capacity (meq/dry g)
1.40
1.78
0.60
1.00
1.20
1.50
1.01
1.00
54
Table 2.2
Synthesis of various samples of pectin based thorium (IV)
phosphate.
Sample Number
PcThP-1
PcThP-2
PcThP-3
PcThP-4
PcThP-5
PcThP-6
PcThP-7
PcThP-8
PcThP-9
PcThP-10
PcThP-11
PcThP-12
PcThP-13
PcThP-14
PclTiP-lS
PcThP-16
% Pectin added
0
1
2
3
5
7
10
11
12
13
15
17
19
20
22
24
Na^ ion exchange capacity (meq/dry g)
0.80
0.85
0.91
1.08
1.10
1.53
1.57
1.60
1.91
i.96
2.15
1.75
1.65
1.60
1.57
1.50
,- V
- < , . _ V .
^ . . • • ' ^
55
Table 2.3
Ion exchange capacity of pectin based cerium (IV) and thorium (IV)
phosphates for various metal solutions.
Metal solution
LiCl
NaNOa
KCl
Mg(N03)2
Ca(N03)2
Sr(N03)2
BaCl2
Ion-exchange capacity (meq/dry g)
PcCeP
1.65
1.78
1.80
1.95
2.15
2.23
2.50
PcThP
1.80
2.15
2.20
2.60
2.80
3.00
3.10
56
2.2.5.2 Effect of eluant concentration on the ion-exchange capacity
The extent of elution was found to depend upon the concentration of the
eluant. Hence a fixed volume (250 ml) of the NaNOs solution of varying
concentrations were passed through the column containing 1 gm of the
exchanger and the effluent was titrated against a standard alkali solution for the
H^-ions eluted out. Table 2.4 summarizes the results of concentration
behaviour on both ion exchange materials.
2.2.5.3 Elution behaviour
The column containing 1 gm of material in H" form was eluted with 1M
NaNOs solution in different 10 ml fractions having a standard flow rate of 0.5
ml/min and 10 ml fractions of the effluent were collected. They were titrated
for the H' -ions released against a standard NaOH solution. This experiment
was conducted to find out the minimum volume necessary for a complete
elution of H' -ions, which reflects the efficiency of the column. The results are
shown in Fig. 2.1 and 2.2 for PcCeP and PcThP respecfively.
2.2.5.4 Recycling studies
1 gm of material was loaded on the column of internal diameter ~lcm,
fitted with a glass wool at its bottom. 7he ion-exchange capacity was
determined by column process (2), using IM NaNOs as eluant. The conversion
of material in H* form was done by passing 250 ml of IM HNO3, maintaining a
very slow flow rate of-0.5 ml/min, then washed the excess of acid with DMW
(pH~7). Table 2.5 shows the result of this study on PcCeP and PcThP.
57
Table 2.4
Concentration behaviour of pectin based cerium (IV) and thorium
(IV) phosphates.
Concentration of
NaN03(M)
0.2
0.4
0.6
0.8
1.0
1.2
Ion-exchange capacity (meq/dry g)
PcCeP
0.61
0.80
1.21
1.52
1.78
1.70
PcThP
0.85
1.25
1.50
1.80
2.15
2.13
58
0.2-1
0.18'
0.16'
0.14-
0.12
0.1
0.08
0.06
0.04-
0.02-
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Volume of Effluent (ml)
Fig. 2.1 Histogram showing the elution behaviour of pectin based cerium (IV) phosphate.
0.25
I 0.2 « 0)
X0.15 t ^ o
* • *
c 5 0.1 '5 cr 0)
= 0.05
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Volume of Effluent (ml)
Fig. 2.2 Histogram showing the elution behaviour of pectin based thorium (IV) phosphate.
59
V5
bX)
S o
• 4 - 1
.a
o .a
s O
• 4 - 1
e
La
u
en
u b£
u >^ B o
"a >
o .t:
o "
« B
5 da ^—s
" b
1 1 a B O
0
H
U u CM
,B H u PM
PM
u u Pk
O R
B
Vi
o "3 >-> u La CM
O U o .a
5 3
6
o o o
o o o o
oo
1—<
o
1—H
O o o oo
OO en ON
(N
--
CN
oo o
oo
in
(N
(
(N O
oo
U-)
(
"Nt-
o
rn
o
^
un
m
<N
in
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ON
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m
\o
in
m in
oo
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CO
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c--
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r-
oo
2.2.5.5 pH Titrations
pH titrations were performed by the Topp and Pepper's method [7]
using an Elico pH meter, model Ll-10 pH meter, on both PcCeP and PclhP.
Various 500 mg portions of the exchanger in the H^-form were placed in each
of the several 250 ml conical flasks followed by the equimolar solution of
alkali metal chlorides and their hydroxides in different volume ratios, the final
volume being 50 ml to maintain the ionic strength constant. The pH of the
solution was recorded after equilibrium and was plotted against the
milliequivalent of the 0H~ ions added. Fig.2.3 and Fig.2.4 shows the result of
this study on PcCeP.and PcThP respcclivel)'.
2.2.5.6 Thermal stability
One gram samples of the material were heated at various temperatures
for Ih each in a muffle furnace, and their ion exchange capacity was
determined by the column process after cooling them to room temperature.
Table 2.6 summarizes the results of this study on PcCeP and PcThP.
2.2.6 Instrumental studies on the ion-exchange materials
2.2.6.1 Thermogravimetric analysis studies
Figures 2.5 and 2.6 show the TGA/DTG curves of PcCcP and Pc fhP
respectively.
0.0
-NaOH/NaCI
-KOH/KCI
-LiOH/LiCI
1.0 2.0 3.0 4.0 5.0 6.0
milliequivalent of OH' ions added
Fig.2.3 Hquilibrium pH titration curves of pectin based cerium (IV) phosphate.
14
I a
NaOH/NaCI
KOH/KCI
LiOH/LiCI
1.0 2.0 30 40 50
milliequivalent of OH ions added
6.0
Fig.2.4 Equilibrium pH titration curves of pectin based thorium (IV) phosphate.
62
m o
3
3
S
•4->
G. (A
o .3 O.
S _3 'u o
,3 • J
"d 3
^3
u "O u v> «
X3
o
es
Pui J3 H PUI
PLH
u CU
3
Q
d ^ ; c/5
^ o^
La 3
3
3
u
1
3 O
*.o ^
L. 3
o u 3
&£ 3
U
Oi UD 3 R
1
3 O
^_^
u o c E H
o 3
3
8 CQ
, 3
(4-1
o 3
3
05
R
n u
J u
A U
, u oi
b t3
u
£
:o "o" u
£
o o
^ ^
3 o
e
»n T — (
cs
o o
^ ^
^ w
' c u
a
00 r-
• ^
oo
OS
^ ^
3 o 6 e
t ^ CD ( N
OS y—t
\>-0\
^ ^
"H u 1-1
O
m r~-
o o ^
t N
en oo
p
o
o oo
^ •5t
oo
^ ^
C/3
'S u
o
m '^t
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m
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c
o JD
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( N !>; • ^ " l >
U • » - '
12 ^
^ t4- l
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m rn
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•<:}•
r4 o
m
>-»
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r-; o
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u -4-»
5*-t|-(
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^
159Cel 8 8%/min
19Cel 99 997%
76CC1 95 648%
90 956%
ISOCel 86 087%
DTG
/
ISlCel 80 996%
DTA
i65Cel 76 943% 392Ce)
74 542% 5S6Cel 72 830%
2"^ 71 503%
0 00 to 00 20 00 30 00 40 OO 50 TO 60 00 T 0^ 80 ^ j 50 0<
Fig. 2.5 Thermogravimetric analysis curve of pectin based cerium (IV) phosphate.
58Cel 1 l%/(rtn
22Cel 99 897%
229Cel 4 7%/m(n
78C<H 93 958%
177Cel 86 705%
226Cel 74 423%
2e7Cel 59 691%
511CS 1 7%/min
•"iSCel ••S 137%
561 Ctl 33 030%
/
DTG
TGA
DTA
' 7 9 C e l ^
/
10 10 00 20 JO JO 00 40 C 50 oc gr jp C 0" an DC gn
Fig. 2.6 Thermogravimetric analysis curve of pectin based thorium (IV) phosphate.
64
2.2.6.2 Scanning electron microscopic studies
Scanning electron micrograph of PcCeP and PcThP were taken at lOOOx
and 2000x magnification respectively as shown in Figures 2.7 and 2.8.
2.2.6.3 Infrared spectroscopic studies
Figures 2.9 and 2.10 show the IR spectra of PcCeP and PcThP
respectively.
2.2.6.4 X-ray diffraction studies
The X-ray pattern of materials were taken using Cu target, with
wavelengths 1.54060 and 1.54439A°. The step size and smoothing width were
0.050 and 0.300 respectively. The step times were 6.00s and 3.00s for PcCeP
and PcThP respectively. Figures 2.11 and 2.12 show the X-ray diffraction
patterns.
65
EHT=15.80 kU UD= 16 nn P h o t o No .= l
Mag= 1.00 K X D e t e c t o r = SEl
Fig. 2.7 Electron micrograph of pectin based cerium (IV) phosphate at 1 OOOxmagnification.
Fig. 2.8 Electron micrograph of pectin based thorium (IV) phosphate at 2000x magnification.
66
1 0 0 :
95 -i
90
8 5 -
80 :
76 T
70 ;
66 ;
60 ;
5 6 -
50 T
46 :
40 -
35 ^
30 -
25 7
20 -2
'5 -
10 z
5 :
^
n r
S
s iti
v>
<o R S cn
S
CO 10
s
00
u>
s f-
;-
£ S
- ^ • ^
2500 2000 Wavenumbws (cm-1)
Fig. 2.9 Infrared spectrum of pectin based cerium (IV) phosphate.
104-
102-
loose 96-
94
92
90
84
82
SO
TS
76
74
72-
70
64
62 -_
60
ii =
2500 2000 WavenumboTB (cm-1)
Fig. 2.10 Infrared spectrum of pectin based thorium (IV) phosphate.
67
2-Theta - Scale
Fig. 2.11 X-ray dif&action pattern of pectin based cerium (IV) phosphate.
\v\^^w^''^^ ^*V1#Ww#l! \^
2-Thcta - Scale
Fig. 2.12 X-ray dif&action pattern of pectin based thorium (IV) phosphate.
68
2.3 RESULTS AND DISCUSSION
This study highlights certain interesting features of the pectin based
cerium (IV) and thorium (IV) phosphates as new fibrous ion exchangers
obtained in the form of sheet. The SEM photographs of PcCeP (magnification
lOOOx) and PcTTiP (magnification 2000x) reveal their particle size as lO im
and 2p.m respectively.
The Na* ion exchange capacity is found to be 1.78 meq/dry g for PcCeP
and 2.15 meq/dry g for PcThP. The i.e.c. alkali metals and alkaline earths on
PcCeP and PcThP show the following trends: Li^<Na^<K^ and
Mg^'<Ca^'<Sr^VBa^^ It is in accordance to the decreasing trend in the
hydrated ionic radii of these metal ions in the same order.
A study of the elution behaviour reveals that the exchange is fast on both
PcCeP (Fig. 2.1) and PcThP (Fig.2.2). Almost all the H^ ions are eluted out in
the first 150 ml of the effluent from a column of 1.0 gm material. The optimum
concentration for the eluant was found to be IM (Table 2.4) for a complete
removal of H" ions from the PcCeP and PcThP columns.
In recycling studies, ion-exchange columns containing these materials
(PcCeP & PcThP) were regenerated repeatedly for many times to study the
retention behaviour of their i.e.c. on recycling. Tabic 2.5 shows that the
retention value decreases slowly with increase in the number of recycles.
PcCeP retains about 11% and PclTiP retains about 3% of their i.e.c. upto 7
recycles.
69
The pH titration curves of PcCeP (Fig.2.3) and PcThlf (Fig.2.4) obtained
under equilibrium conditions for LiOH/LiCl, NaOH/NaCl and KOH/KCl
systems, which indicate a monofimctional exchange process for both materials.
The materials release H^ ions easily with the addition of metal salt solution
containing no OH" ions, showing a strong cation exchange behaviour. At low
metal hydroxide concentration, the ion exchange for Li ions is lower than Na
and K ions as is evident from the initial pH at a lower hydroxide
concentration. Also, the exchange rate slows down for the H^-Li^ exchange
than for the H*-Na^ and H -K" exchanges. The H^-Li* exchange process is
completed at higher 0H~ concentration. This may be due to a larger hydrated
radius of Li" ion than those of Na* and K^ ions, thus accounting for a lower ion
exchange capacity for Li ion in the column process (dynamic condition) where
the equilibrium is not fully established. The end point in the titration is not
quite sharp which may be due to some alkaline hydrolysis of the ion exchanger.
An overall higher ion-exchange capacity for all the three metal ions in the
batch process (static condition) than in the column process, as shown by the
potentiometric curves, may be due to the presence of alkali hydroxides which
facilitates the ion exchange by the removal of H^ ions from the external
solution in accordance with the Le Chatelier's principle.
Thermal studies of these materials indicate certain very interesting
results. Both of them are highly stable on heating as they retain about 97% of
their i.e. c. on heating upto 100°C and about 81% on heating upto 200°C. On
heating upto 400°C however they show a marked difference in the retention
70
capability of their i.e.c. PcCeP showing retention of 74% while PcThP
showing retention of 64%. Even on heating upto 600°C these materials show
an appreciable i.e.c, PcCeP retaining about 64% and PcThP about 33%. PcCeP
retains it i.e.c. upto 28% even on heating upto 800°C however the i.e.c. of
PcThP sharply decreases on heating upto this temperature, showing only 6%
retention. This is a unique behaviour of these materials as compared to the
other ones of this class studied earlier. AACeP[5] loses its i.e.c. about 60% at
200°C and 95% at 400°C, while AAThP[4] loses its i.e.c. almost totally beyond
200°C.
The thermograms, (Figures 2.5 and 2.6) show 9.04% weight loss upto
151°C in PcCeP and 13.2% weight loss upto 177°C in PcThP, which may be
due to the removal of external water molecules from the exchanger. Beyond
151*'C tiie condensation of PcCeP must have started, resulting in the
dehydration due to the removal of strongly coordinated water molecules from
the framework of the exchanger, which continues upto 1000°C, where the
weight becomes almost constant. It also involves the production of Ce02 at
450°C [8]. In PcThP, the condensation starts at 177°C as is indicated by a
weight loss up to ~415°C. On further heating an abrupt change was observed.
At 561°C, ThOa horizontal starts [9], indicating the formation of
pyrophosphate.
The elemental analysis gave the molar ratio of C, H, N as 3: 77: 1 and
31: 80: 1 for PcCeP and PcThP respectively.
71
The IR spectrum of PcCeP (Fig.2.9) and PcThP (Fig.2.10), confirms the
presence of metal oxide and metal hydroxide bands in the material. The metal
oxygen and metal hydroxide bands are observed at 619.8 c m ' PcCeP and
627.73 and 671.59 cm"' in PcThP. The bands at 417.00, 500.87 and 1057.66
cm"' in PcCeP and 526.52 and 1074.84 cm"' in PcThP indicate the presence of
phosphate groups. The absorption bands at 1633.43 £md 3407.31 cm"' in PcCeP
and 3353.21 cm"' in PcThP, corresponds to the water of crystallization. The
bands at 2355.80 cm"' in PcCeP and 1367.23, 1430.70 cm"' and 2933.97 cm"'
in PcThP, mdicate the C-H stretching of carbon. The C^O stretching of ester
was observed at 1737.61 cm"' in PcCeP and 1235.36 and 1746.14 c m ' in
PcThP. The absorption bands at 1017.47 and 1235.36 cm"' in PcThP indicate
C-0 stretching in alcohols [10].
The X-ray diffraction pattern of PcCeP and PcThP, shows its amorphous
nature.
72
REFERENCES
1. K.G. Varshney, Solid State Phenomena, 90-91 (2003) 445.
2. K.G. Varshney, Namrata Tayal and U. Gupta, Colloids Surf. A
Physicochem. Eng. Asp., 145 (1998) 71.
3. K.G. Varshney, Namrata Tayal, A.A. Khan and R. Niwas, Colloids Surf.
A. Physicochem. Eng. Asp., 181 (2001) 123.
4. K.G. Varehney and Namrata Tayal, Langmuir, 17 (2001) 2589.
5. K.G. Varshney, Puja Gupta and Arun Agarwal, Proceedings of the
National Symposium on Biochemical Sciences: Health and
Environmental Aspects, Dayalbagh Educational Institute, Dayalbagh,
Agra, Allied Publisher, New Delhi (2003) pp.254-257.
6. K.G. Varshney, Puja Gupta and Namrta Tayal, Indian J. Chcm., 42(A)
(2003) 89.
7. N.E. Topp and K.W. Pepper, J. Chem. Soc, 3299 (1949).
8. C. Duval, "Inorganic Thermogravimetric Analysis", Elsevier,
Amsterdam (1953), pp.403.
9. C. Duval, "Inoganic Thermogravimetric Analysis", Elsevier,
Amsterdam (1953), pp.492, 497.
10.R.T. Morrison and R.N. Boyd, "Organic Chemistry", Prentice Hall of
India Pvt. Ltd., New Delhi (1998). <^^:T7 . -^
^ { ' - C . } ' ' ^
• : - . ' \ • •'-' f