Chapter - IV
MATERIALS AND METHODS
4.1 General
The following materials and methods adopted according to the specifications
given below are used in the present study.
4.2 Chemicals & Reagents
Compounds chosen for the present study along with their molecular weight
and structures are presented in Table 4.1. 4C-2NP, 2,4,6-T, 2C-4NP, 4C-3MP &
2C-5MP purchased from Sigma Aldrich are all of analytical grade. H2O2 solution
(30%, reagent grade) is procured from Lobacheme. Non-porous P-25 TiO2 powder
(80% anatase, average diameter 0.02 µm and surface area ~50 m2/g) is a gift from
Degussa Corporation (Pune, India). FeSO4.7H2O (Ferrous Sulphate) as the source
of Fe (II), H2SO4 (Sulphuric acid) & NaOH (Sodium hydroxide) are purchased from
Merck. All the chemicals used in the present study are of analytical grade. Glass
distilled water is used for the entire study.
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S.No
Name of the compound
Structure
Mol.Wt.
OH
1
NO2
4C-2NP
173.55
Cl
OH
Cl
2
2C-4NP
173.55
NO2
OH
3
2C-5MP
Cl
142.58
H3C
OH
4
4C-3MP
142.59
CH3
Cl
OH
5
2,4,6 T
Cl
Cl
Cl
Table 4.1 Phenols chosen for the study
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197.46
4.3 Reactor set-up
All the experiments are performed in a cylindrical photo reactor (Plate 4.1)
with a total volume of 1.0L (diameter 12cm and height 13.3cm). The reactor is
encased in a quartz tube to protect it from direct contact with an aqueous solution
flowing through an annulus between the inner surface of the vessel and the outer
surface of the quartz tube, located at the axis of the vessel. The reactor is provided
with inlets for feeding reactants, and ports for measuring temperature and
withdrawing samples. The reactor is open to air with a Teflon coated magnetic
stirring bar placed in the bottom for homogenization. The UV irradiation source is
a 16W low-pressure mercury vapour lamp (maximum emission at 270nm) encased
in a quartz tube. The lamp was axially centered and was immersed in the solution
containing the respective phenolic solutions. A gas tight syringe is used to collect
the sample at regular intervals from the sample-port of the reactor. Figure 4.1
shows the schematic diagram of the laboratory scale photochemical installation
used in the study.
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Plate 4.1 Internal view of the photo reactor
Figure 4.1 Schematic of 16W UV Photo Reactor
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4.4 Experimental Set-up
Desired quantities of substituted phenols (SPs) is weighed and dissolved in
methanol to prepare stock solution. The shelf life of the stock solutions was
maintained for 1 week. Further dilutions are made from stock solution. All the
stock solutions, standards and pure compounds are stored in dark below room
temperature.
The
samples
are
brought
to
room
temperature
before
experimentation. Control samples are run for every experiment to validate the
degradation and also check for any loss on volatalization. Solutions are treated at
different pH values. The adjustment of pH is made with 0.1 N /1.0N solution of
H2SO4 or 0.1N/1.0N NaOH.
Experiments are carried out in batch mode. Different concentrations of H2O2
and Fe+2 in the ratio of 10:1 are used for optimization in Fenton and photo Fenton
experiments. In case of UV/H2O2, the concentration of hydrogen peroxide to
phenolic solution is maintained in the ratio of 1:1. TiO2 dosage is varied from 0.1g
– 0.5g at an interval of 0.1g in UV/TiO2 experiments. The reaction mixture is
homogenized by magnetic agitation for 15min before introducing in to the photo
reactor. Samples are withdrawn at regular intervals and centrifuged, followed by
filtration through 0.25μm syringe filters (mdi, India type SY25NN). The filtrate is
stored at 4°c and further analyzed for compound reduction and COD removal. In
order to arrest oxidation after treatment time, the filtered samples are quenched
by adding 10% Na2SO3 aqueous solution [89]. The total treatment time of the
experiment is selected so that at least 90% degradation of initial compound is
achieved.
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4.5 Analytical procedure
4.5.1. UV-Vis Spectrophotometer
The quantitative decrease in the concentration of SPs is measured by
Systronics-1272 UV-Vis Spectrophotometer (wavelength 254nm). This double
beam spectrophotometer has inbuilt tungsten and deuterium lamps, which
provide the measurement of OD in the range of 200-800nm (near UV and Visible
regions). The samples are analyzed using quartz cuvette, as it has zero absorption
in the above wavelength region. The solutions are scanned within a wavelength
range of 200-800nm to get absorption maximum of respective SPs followed by
preparation of calibration curves. The corresponding concentration of the
experimental sample was obtained from the calibration curves.
4.5.2. High Performance Liquid Chromatography
Reverse phase HPLC (Agilent) consists of a binary pump system, Rheodyne
injector with a photodiode array detector and is supported by Chemsoft.
Separation is performed by a Nova Pack reverse phase C18 column. For 4C-2NP,
mobile phase is a mixture of methanol and water (80:20) isocratically delivered by
a pump at a flow rate of 1ml/min and wavelength of 254nm. For 2C-4NP, the
eluent stream consisted of 80% water, and 20% acetonitrile pumped at 0.8
ml/min at 280nm for 2C-4NP. For 2C-5MP, 4C-3MP & 2,4,6 TCP, the mobile phase
(methanol and water 70:30, v/v) flow rate is set to 1ml/min at 360nm and 290nm
with a retention time of 30min.
4.5.3. Chemical Oxygen Demand
COD was calculated as per the standard method No. 5220C, page no. 5 – 14
from STANDARD METHODS for the examination of water and wastewater (1989),
17th edition. For all the samples 1:1 dilution was done so as to get the COD within
70
range while using the above method. Samples were digested in a semi-automatic
autoclave.
4.5.4.
pH
pH is measured using pH meter (M/s. Systronics, India).
4.6 Degradation of the substituted phenols (SPs)
Degradation of the selected SPs using various AOPs is examined at different
operational parameters. A series of experiments are carried out to evaluate the
degradation trends and further rate kinetics is determined.
4.6.1 Photodegradation using UV light (Direct photolysis)
The photo reactor is charged with 0.75L of aqueous solution of SPs with an
initial concentration ranging between 50-750ppm. To determine the optimum pH
for the degradation of SPs under direct UV photolysis, experiments are carried
with pH ranging from 3-11, and the adjustment of pH is made with 0.1 N /1.0N
solution of H2SO4 or 0.1N/1.0N NaOH. The samples are irradiated for a period of
3hrs with a sampling interval of 30min.
4.6.2 Photodegradation using UV light in the presence of Hydrogen peroxide
(UV/H2O2)
The reactor is charged with 0.75L of aqueous solution of SPs with an initial
concentration of 100ppm of SPs. In order to choose the effective concentration of
hydrogen peroxide for the degradation of SPs, the concentration of hydrogen
peroxide to SPs is maintained in the ratio of 1:1. To study the effect of initial pH, a
series of experiments are carried at different pH values ranging from 3 to 11. All
the experiments are carried out in batch operation. Samples are withdrawn at
regular intervals of 30min and analyzed for compound and COD reduction.
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4.6.3 Degradation using Fenton & Photo Fenton process
The reactor is always charged with 0.1L for Fenton & 0.75L for Photo-fenton
experiments of an aqueous solution of 100ppm of SPs. Different concentrations of
H2O2 and Fe+2 in the ratio of 10:1 are used for optimization in Fenton and photo
Fenton experiments. Results reported in the relevant literature clearly indicate
that the operation pH determines the degree of oxidation reached in the treatment,
with pH 3.0 being the most effective value (90), hence in the present study the
Fenton and photo Fenton experiments are performed at an acidic pH of 3.0±0.1.
The reaction mixture is homogenized by magnetic agitation for 15min before
introducing in to the photo reactor. Samples are withdrawn at regular intervals of
30 min and centrifuged, followed by filtration through 0.25μm syringe filters. The
samples are then analyzed for compound and COD reduction.
4.6.4 Photodegradation using UV light in the presence of TiO2 as catalyst
The reactor is charged with 0.75L of aqueous solution of SPs with an initial
concentration of 100ppm of SPs. TiO2 dosage is varied from 0.1 to 0.5 g at an
interval of 0.1g in UV/TiO2 experiments. The reaction mixture is homogenized by
magnetic agitation for 15min before introducing in to the photo reactor. Before
each analysis, samples are centrifuged and filtered on 0.25 μm Millipore
membranes to remove TiO2.
4.7
Comparison of various AOPs studied
A comparative assessment of SPs degradation by different AOPs (UV, UV/
H2O2, Fenton, UV/Fenton and UV/TiO2) is performed in terms of compound and
COD reduction after optimization of all the parameters. Finally, kinetic constants
are evaluated to determine the degradation efficacy.
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4.7.1 Compound and COD reduction
The quantitative decrease in the concentration of SPs is measured by
Systronics-1272 UV-Vis Spectrophotometer at their respective absorption maxima.
The compound reduction is further validated with high performance liquid
chromatography (HPLC). COD is measured according to standard methods.
Percentage reduction of compound/ COD is calculated by the equation:
% reduction
=
C0-Ct
× 100
Ct
Where C0 represents initial concentration/COD of the compound
Ct represents final concentration/COD of the compound
4.7.2 Degradation rate
The degradation of SPs is investigated for the AOP systems (UV, UV/H2O2,
Fenton, Photo fenton, and UV/TiO2) and the experimental data is fitted using
pseudo first order kinetics. The rate constants are evaluated using linear
regression analysis by plotting ln Ct/C0 versus reaction time.
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