PHOTOCATALYTIC DEGRADATION OF  2,4,6-TRICHLOROPHENOL
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PHOTOCATALYTIC DEGRADATION OF 2,4,6-TRICHLOROPHENOL USING Ag@TiO2 NANOPARTICLES. Under the guidance of Dr.Vidya Shetty.K. Presented by Y. Sri Lakshmi 07PD06F. Introduction:.

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PHOTOCATALYTIC DEGRADATION OF 2,4,6-TRICHLOROPHENOL

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PHOTOCATALYTIC DEGRADATION OF 2,4,6-TRICHLOROPHENOL

USING Ag@TiO2 NANOPARTICLES

Under the guidance of Dr.Vidya Shetty.K

Presented by

Y. 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


Photocatalysis

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


  • Experimental procedure for continuous operation

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.


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


CALIBRATION GRAPH

Calibration plot for TCP analysis


Results and Discussion

  • Characterization of the catalysts

  • X-rays diffraction (XRD)

  • Scanning Electron Microscopy


  • X-rays diffraction (XRD):

XRD pattern of Ag@TiO2 nanoparticles

Particle size corresponding to selected peak


Scanning Electron Microscopy (SEM) :

SEM micrographs of core/shell structured Ag@TiO2composite 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/gACcore-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.


  • 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:


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@TiO2nanoparticles.


  • From the batch studies on photocatalytic degradation of 2,4,6-TCP with Ag@TiO2nanoparticle 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@TiO2nanoparticle. 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@TiO2nanoparticles 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.


SCOPE FOR FUTURE WORK

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@TiO2nanoparticle immobilization.

2. To study the photocatalytic degradation by fluidized bed reactor

3. To obtain optimum ratio of Ag@TiO2nanoparticle to TCP loading for photocatalytic degradation.


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