PHOTOCATALYTIC DEGRADATION OF 2,4,6-TRICHLOROPHENOL

USING Ag@TiO2 NANOPARTICLES

Under the guidance of Dr.Vidya Shetty.K

Presented byY. Sri Lakshmi 07PD06F

Introduction:

Chlorophenols are organic chemicals formed from phenol by

substitution in the phenol ring with one or more atoms of chlorine.

The compounds of interest in the organochlorine family are

2,4,6-Trichlorophenol(TCP) and pentachlorophenol.

Exposure to TCP produces Leukamias,Liver cancer, Soft tissue

sacomas, Hydgkin’s.

Many literatures have reported that a lot of toxic or hazardous

industrial chemicals could be destroyed by photocatlytic

degradation.

Photocatalysis is a new technique of decontamination of

chlorophenols

Photocatalytic process efficiency can be increased by the use of

catalyst nanoparticles

Objective of the project

The main objective is to study the photocatalytic degradation of TCP

using Ag@TiO2 nanoparticles .

The specific objectives include:

To study the effect of initial concentration of TCP , catalyst loading,

UV lamp power and initial solution pH on the TCP degradation by

carrying out batch experiments with suspended Ag@TiO2 nanoparticles.

To obtain the optimum values catalyst loading and initial solution pH

for TCP degradation

To evaluate the rate equation and the kinetic parameters for the TCP

degradation by Ag@TiO2 under optimum conditions.

To study the effect of catalyst loading on TCP removal in a packed

bed reactor with nanoparticles immobilized on activated carbon

particles under continuous mode of operation.

Preparation of Ag@TiO2 nanoparticles

The colloidal solution of TiO2 coated silver particles was prepared as per

the reported procedure by Kamat et.al[ 2004].

Ag@TiO2 nanoparticles:

2ml of 15mM AgNO3 solution was mixed with 18 ml of 8.3mM TTEAIP

solution.

10 ml of DMF was then added into TTEAIP-Ag solution.

The solution was stirred first for 15 min at room temperature and then

refluxed at 80oC with continued stirring.

After 15min , the color of suspension turned to dark brown from light

brown. At this point heating was stopped and suspension was stirred until it

cooled to room temoerature.

The cluster suspension of Ag@TiO2 was three times centrifuged and

suspended in ethanol solution.

Schematic diagram of the laboratory-scale reactor for nanoparticle synthesis

Preparation of Ag@TiO2 film immobilized on Activated Carbon

Immobilization of Ag@TiO2 nanoparticles on AC was done as per the

procedure reported by Bing et.al (2008) for immobilization of TiO2 film on

ceramics glaze

45g of Activated carbon of size 2.8/2 mm was washed with distilled water

and dried in an oven at 100-120oc for 2hrs.

The Activated carbon was completely immersed in Ag@TiO2 nanosolution

in water. The beaker with nanosolution and AC were kept in a rotary shaker at

200rpm for 10 min.

These particles with immobilized nanoparticle were then dried in oven at

100-120oc for 2hrs and then used in continuous experiments.

Characterization of the catalysts

X-rays diffraction (XRD)

Scanning Electron Microscopy

Experimental procedure for batch operation

A 150mL solution of 2,4,6 Trichlorophenol of required concentration

was prepared by dissolving required quantity of TCP in distilled water. The

required amount of catalyst was added into the reactor. Air at a flow-rate of

0.1Lmin−1 was bubbled through the suspension. The suspension was

magnetically stirred continuously. At the start of the experiment UV source which

are two numbers UV lamps are placed at a fixed distance of 7cm on either side of

the reactor were put on. Samples of 2mL were withdrawn from the reactor at

different time intervals. The withdrawn samples were filtered with two numbers of

0.25μm Millipore filters for removal of the nanoparticles. These samples were

analysed for TCP using Hitachi UV-160 A spectrophotometer. The results are

based on average temperature of 35oc. The concentration of 2,4,6 -Trichlophenol

as a function of irradiation time were obtained. Analysis of each sample was

repeated three times and the concurrent was used.

Schematic diagram and photographic image of the

laboratory-scale photochemical reactor for Batch studies

A general reaction scheme for the heterogeneous photocatalytic oxidation of chlorophenols is

Photocatalysis

Synthetic waste water of the required concentration of 2,4,6 -

Trichlorophenol concentration was prepared by dissolving calculated

amount of TCP in water. The reactor was operated at room temperature

and packed with 45 g of 2.8/2 mm granular activated carbon

immobilized with Ag@TiO2. Air at a flow-rate of 1Lmin−1 was bubbled

through column. Water was pumped to the bottom of the column at

required flow rate. At the start of the experiment UV source, placed at a

fixed distance of 7cm from the reactor was put on. Samples of 2mL

were collected at outlet at different time intervals. The withdrawn

samples were filtered with two numbers of 0.25 μm Millipore filters to

remove the AC fines. The clear solution was separated and analysed for

TCP concentration using Hitachi UV-160 A spectrophotometer.

Analysis of each sample was repeated three times and the concurrent

was used.

Experimental procedure for continuous operation

Schematic diagram and photographic image of photochemical reactor for continuous operation

Spectroscopy Calibration

Preparation of TCP solution

Reagents Preparation:

Ammonium hydroxide,NH4OH(0.5N)

Phosphate buffer solution

Potassium ferricyanide solution

4-aminoantipyrine solution

Calibration Procedure

For each of the prepared 100ml std sols,2.5ml of 0.5N NH4OH

solution was added and immediately adjusted to pH 7.9+0.1 with

phosphate buffer, and then 1ml of 4-aminoantipyrine solution was

added and thoroughly stirred.Finally 1ml of K3Fe(CN)6 was added

and mixed well.The solution was left for 15min the standard

solutions were transferred to the cell and the absorbance was

read against blank at 510nm using Hitachi UV-160A

spectrophotometer

From the values of absorbance and concentration of tcp presented will

get calibration curve. To get the concentrations of unknown sample ,

sample taken in a 100ml std flask. the above said reagents were added

and mixed well. Flask was made up to 100ml by adding distilled water.

The solution was left for 15min.The sample and blank were transferred

to the cell and absorbance's were read. The absorbance was

interpretated with the calibration curve and concentration of unknown

samples were obtained

Calibration table for TCP analysis

SI No. Concentration (ppm)

Absorbance

1 0 0.00

2 1 0.111

3 2 0.218

4 3 0.333

5 4 0.442

6 5 0.566

CALIBRATION GRAPH

Calibration plot for TCP analysis

Characterization of the catalysts

X-rays diffraction (XRD)

Scanning Electron Microscopy

Results and Discussion

X-rays diffraction (XRD):

selected peak 2Ѳ1 2Ѳ2 β=(2Ѳ2-2Ѳ1)/2 L=k λ/ βcos Ѳ

38.48o 38.4 38.6 0.1 84.2

39.1o 39.009 39.305o 0.1075 78.5

Particle size corresponding to selected peak

XRD pattern of Ag@TiO2 nanoparticles

Scanning Electron Microscopy (SEM) : SEM micrographs of core/shell structured Ag@TiO2 composite particles with EDAX

SEM Micrograph of the Activated Carbon increase of 500 times.

SEM Micrograph of the Activated Carbon increase of 2000 times

SEM micrographs of Activated carbon with EDAX

SEM with EDAX micrographs of Activated Carbon immobilized with

0.05gAg@TiO2/gAC core-shell structured Ag@TiO2 composite particles before

and after reaction

Batch studies

Batch experiments on photocatalytic degradation of 2,4,6-TCP with

Ag@TiO2 nanoparticles in suspension in 150mL reactor volume was conducted to

study the effect of catalyst loading, initial 2,4,6-TCP concentration, initial solution

pH and UV lamp power.

Effect of catalyst loading:

Effect of photocatalyst loading on 2,4,6-TCP degradation: initial concentration 50 ppm, air flow rate 0.1L min−1, natural pH, time 24 hrs, temperature 35 ◦C, UV lamp 40W.

Effect of photocatalyst loading on 2,4,6-TCP degradation: initial concentration

50 ppm, air flow rate 0.1L min−1, natural pH, time 24 hrs, UV lamp 40W

Effect of photocatalyst loading on initial rate of degradation of 2,4,6-TCP :

initial concentration 50 ppm, air flow rate 0.1L min−1, natural pH, time 24 hrs,

UV lamp 40W

Effect of initial solution pH on Batch degradation

Effect of initial pH on 2,4,6-TCP degradation: temperature 35 ◦C, photocatalyst loading 0.03% (w/w), excess air flow rate 0.1 L min−1, initial TCP concentration 50 ppm, time 24 hrs, UV lamp 40W.

Effect of initial pH on 2,4,6-TCP degradation:, photocatalyst loading 0.03%

(w/w), air flow rate 0.1 L min−1, initial TCP concentration 50 ppm, time 24

hrs, UV lamp 40W.

Effect of UV lamp power on Batch degradation of TCP

Effect of UV lamp power on 2,4,6-TCP degradation: photocatalyst loading

0.03% (w/w), air flow rate 0.1 L min−1, initial TCP concentration 50 ppm,

pH=3.

Initial rate of degradation of 2,4,6-TCP at different UV lamp power

during the batch operation, initial concentration 50 ppm, 0.03%(w/w)

catalyst loading, air flow rate 0.1 L min−1, initial solution pH 3.

UV lamp power(watts) Initial rate(µMmin-1)

40 2.96

80 3.12

Effect of initial concentration of 2,4,6-TCP:

Effect of initial concentration on 2,4,6-TCP degradation: Catalyst loading

0.03% (w/w), natural pH, time 24 hrs, UV lamp 40 W, air flow rate 0.1 L

min−1.

Effect of initial concentration on 2,4,6-TCP initial rate of degradation

during the batch operation, 0.03%(w/w)catalyst loading, air flow rate 0.1

L min−1, natural pH, UV lamp 40W.

Kinetic analysis:

Concentration rate constant (min−1)

253 0.002

177.2 0.003

101.2 0.003

Effect of initial concentration of 2,4,6-TCP degradation on

reaction rate constant: catalyst loading 0.03% (w/w), initial

solution pH 3, time 24 hrs, UV lamp 40W, air flow rate 0.1L min−1.

The experimental data can be rationalized in terms of the modified

form of Langmuir–Hinshelwood kinetic treatment, which has

already been successfully used to describe solid–liquid reactions.

The rate of unimolecular surface reaction is proportional to the

surface coverage assuming that the reactant is strongly adsorbed

on the catalyst surface than the products. The effect of solute

concentration on the rate of photocatalytic degradation is given in

the form of the following equation:

where k1, k2 and C0 are adsorption constant, specific rate constant

and initial concentration of TCP in µM respectively. The

applicability of equation was confirmed by the linear plot obtained

by reciprocal of initial rate 1/r against reciprocal of initial

concentration of the TCP 1/Co.

Effect of initial concentration of 2,4,6-TCP degradation on

reaction rate constant: catalyst loading 0.03% (w/w), natural pH,

time 24 hrs, UV lamp 40W, air flow rate 0.1L min−1.

Effect of catalyst loading during Continuous operation:

Effect of photocatalyst loading on 2,4,6-TCP degradation during continuous operation: initial concentration 50 ppm, excess air flow rate 0.1mL min−1, natural pH, temperature 35 ◦C, UV lamp 40W.

CONCLUSIONS

Based on the results of present investigation and from the available scientific

information derived from the review of the relevant literature, following

conclusions are drawn

Photocatalytic degradation of TCP can be efficiently carried out using

nanoparticles. The initial rate of degradation increases with catalyst loading

up to a value and then decreases in batch degradation studies.Catalyst loading

0.03% was found to be optimum for 50ppm initial TCP concentration

It was found from the Batch studies that with increase in pH of TCP

solution from 2.0 to 3.0 degradation of TCP has increased. Further increase

in pH from 3.0 to 9.0 has lead to decrease in TCP degradation. pH 3 was

found to be the optimum for photocatalytic degradation of TCP by

Ag@TiO2 nanoparticles.

From the batch studies on photocatalytic degradation of 2,4,6-TCP

with Ag@TiO2 nanoparticle with different UV lamp power, it can be

concluded that with increase in UV lamp power the initial rate of

degradation increases, But the ultimate degradation at the end of 24hrs

remained the same.

The initial rate of degradation increased with increase in initial TCP

concentration.

Kinetic model was formulated for the photocatalytic degradation of 2,4,6-TCP

solution with Ag@TiO2 nanoparticle. The photocatalytic degradation of TCP

obeyed pseudo first order kinetics and the rate constant is 0.0027min-1.

Continuous experiments on photocatalytic degradation of 2,4,6-TCP with

Activated carbon immobilized with Ag@TiO2 nanoparticles at different catalyst

loadings was conducted. It can be concluded that the steady state percentage

degradation increased with increased catalyst loading. And maximum 60%

degradation of 50ppm TCP could be achieved in continuous reactor.AC particles

are not suitable to be used as nanoparticle support materials in photocatalytic

reaction.

Based on the results of present investigation the following suggestions

are made for future research as a logical continuation of present work

1.To study the performance packed bed reactor with different support

materials for Ag@TiO2 nanoparticle immobilization.

2. To study the photocatalytic degradation by fluidized bed reactor

3. To obtain optimum ratio of Ag@TiO2 nanoparticle to TCP loading

for photocatalytic degradation.

SCOPE FOR FUTURE WORK

1) mez-De Jesu .A. G., Romano-Baez .F.J., L. Leyva-Amezcua. L. , Jua rez-Ramı rez .C.,Ruiz-OrdazN., Gal

ındez-Mayer.J. (2009) “ Biodegradation of 2,4,6-trichlorophenol in a packed-bed biofilm reactor equipped

with an internal net draft tube riser for aeration and liquid circulation” J. Hazard. Mater. 161, 1140–1149

2) Kathiravan.A., Kumar.P.S., Renganathan.R., Anandan.S.(2008) “ Photoinduced electron transfer reactions

between meso-tetrakis (4-sulfonatophenyl) porphyrin and colloidal metal-semiconductor nanoparticles”

Colloids Surf A Physicochem. Eng. Aspects.

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salicylic acid using ZnO catalyst” J. Hazard. Mater.

4) Estevinho.B.N., Martins.I., Ratola.N., Alves.A., Santos.L.(2007) “ Removal of 2,4-dichlorophenol and

pentachlorophenol from waters by sorption using coal fly ash from a Portuguese thermal power plant” J.

Hazard. Mater. 143 ,535–540

5) Hameed.B.H.(2007) “Equilibrium and kinetics studies of 2,4,6-trichlorophenol adsorption onto activated

clay” Colloids Surf A Physicochem. Eng. Aspects 307 ,45–52.

6) Rotta .H.C.E.L. “ Chloroperoxidase mediated oxidation of chlorinated phenols using electrogenerated

hydrogen peroxide”Electronic Journal of Biotechnology ISSN: 0717-3458

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EE&S 845 Environmental Engineering Chemistry II:Environmental Organic Chemistry

Spring,http//www.leeorg1.htm

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