2.1. Reagents and chemicalsAll the

2.1. Reagents and chemicals
All the chemicals used in the present study are of A.R. grade
and are obtained from companies of repute. Zinc acetate monohydrate
(99.9%, Merk, India) and N,N-dimethylformamide (DMF)
(99.9%, Thomas Baker) are used as supplied without further purification.
Natural bentonite is procured from M.D. Chemicals (Pune,
India), while phenol crystals (Mw 94.11, pH 4.8–6.0) were procured
from S.D. Fine Chemicals, India. Demineralized water was used for
preparation of reagents solutions.
2.2. Synthesis of nano ZnO–bentonite clay composite
The synthesis procedure mainly consists of purification of bentonite
clay followed by in situ intercalation of clay with nanosized
ZnO. The bentonite sample was ground and sieved to 200-mesh size
then washed with demineralized water for 3–4 times. The slurry of
bentonite prepared water was stirred for 1 h, kept overnight, filtered
under vacuum and the resultant solid cake was exposed to
slow evaporation till the completely dry material was obtained.
The purified clay was used for the synthesis of nanocomposites
described as follows: 10 g of purified bentonite was added to a
solution containing 2 g zinc acetate dihydrate dissolved in 250 ml
of DMF and the mixture was sonicated for about 3 h in order to
obtain homogeneous suspension. To this solution, 100 ml of 0.1 M
NaOH/H2O solution was added with constant stirring for 1 h. The
nanocomposites powder was obtained after successive centrifugation
and dispersions in alcohol and the solid mass was dried at 75 ◦C
under vacuum for 4 h and calcinated at 200 ◦C for 2–3 h. The dried
ZnO–bentonite nanocomposite was then used for photocatalytic
experimentation.
The paste of nanoclay bentonite was prepared by mixing 2 g of
nanoclay bentonite with 0.1 g of polyethylene glycol (Mw 6000) and
0.5 ml of transparent clear commercially available epoxy resin this
mixture paste was prepared in 4 ml ethanol and water mixture.
Homogeneous paste was prepared in automatic pigment Muller.
Paste was applied onto MS plate using bar coater and then it was
dried at 110 ◦C. The thickness of the coating film on MS plate was
maintained between 50 and 90 m using bar coater. Thickness was
determined using the mass and area of the coating. Weight was
taken before and after coating of paste. The determined thickness
was confirmed using dry film thickness meter gauge. The MS plate
is 15 cm × 5 cm was used as support on which catalyst was coated.
2.3. Characterization of nanocomposite
XRD diffraction patterns of natural bentonite, ZnO–bentonite
nanocomposite are recorded on powder X-ray diffractometer
(Philips PW 1800) with Cu K˛ radiation (LFF tube 35 kV, 50 mA).
Scanning electron microscopy (SEM) image was taken on JSM-
6400 (JEOL). Transmission electron microscopy (TEM) image was
taken on a Philips Tecnai 20 model, which has resolution of 2 ˚A
unit and AC voltage 200 kV. FTIR spectra are of ZnO–bentonite
nanocomposite before and after phenol treatment are recorded on
FTIR Spectrophotometer (Perkin-Elmer, model BX2) in the range
4000–400 cm−1.
2.4. Phenol degradation experiments
2.4.1. Batch experiments
Photocatalytic experiments were carried out with a known
quantity of catalyst added to 2000 ml reaction flasks containing
1000 ml of an aqueous solution of phenol within the concentration
range of 200–1000 mg L−1. The solution was irradiated in a closed
box with a UV lamp Spectroline XX-15N which emits radiation at
365 nm with intensity of 2000 W/cm2. During the experimentation,
the sample was taken out from the flask after a definite time
interval and is analyzed using UV–Vis spectrophotometer (SHIMADZU
160A model) at max 269 nm.
2.4.2. Under Continuous Stirred Tank Reactor (CSTR)
To understand the distribution of residence time of CSTR, Pulse
input of 5 ml (1 N aqueous solution) methylene blue dye tracer was
injected into CSTR. The output of reactor was measured using UV
spectrophotometer. The ‘C’ and ‘E’ curve of CSTR was plotted and
average residence time was calculated.
For the photodegradation of phenol, experimental setup consists
of ZnO–nanoclay composite coated MS plate inserted in
the phenol solution with continuous irradiation with UV lamp
from the sidewalls of glass reactor under continuous stirring as
shown in Fig. 1. The feed was regulated by the calibrated feeding
pump (peristaltic pump). Flow of phenol solution through
CSTR reactor was regulated with the help of peristaltic pump
(Neolab Instruments, Mumbai). The distance between solution
and UV-source (UV lamp Spectroline XX-15N) was kept constant
throughout the experimentation. Dimensions of MS plate
are 15 cm × 5 cm on which catalytic materials is coated. The distance
from the UV source is 15 cm from center of plate support of
photocatalyst.
During irradiation, agitation was maintained by magnetic
stirrer (Remi Equipments, India) at 400 rpm to keep the suspension
homogeneous. The concentration of phenol was