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
spectrophotometer
at
510nm
using
Hitachi
UV-160A
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.
1
Concentration
(ppm)
0
Absorbance
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
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
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
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:
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.
Concentration
rate constant (min−1)
253
0.002
177.2
0.003
101.2
0.003
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
Ag@TiO2 nanoparticles.
TCP by
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.
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@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.
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