The montmorillonite sample supplied by PT. Tunas Inti Makmur,
Indonesia was firstly activated with 0.5 MH2SO4 solution under reflux
for 6 h. The solid was filtered and washed with double distilled water
until the filtrate pH was 7. The chemicals used, zinc chloride
(ZnCl2·2H2O), NaOH, H2SO4, cetyl trimethyl ammonium chloride
(CTMACl), methylene blue and H2O2 were supplied by Merck. Before
metal dispersion, a clay suspension was prepared by diluting 5 wt.%
montmorillonite powder in aquadest with the addition of CTMACl
drop by drop at 2.5 mmol CTMACl/g-montmorillonite stirred at room
temperature overnight. A pillarization agent of zinc chloride was
prepared by mixing zinc chloride and NaOH at 1:1 M concentration in
H2O:isopropanol (50:50) solution with vigorous stirring for 4 h. The
Zn2+ precursor solution was then dropped slowly into the montmorillonite
suspension to achieve a 5.0 wt.% Zn loading. The mixture was
stirred overnight and then was filtered and washed using deionized
water until the filtrate had pH 7 and was free from Cl− ions (AgNO3
test). The solids were dried in an oven for overnight and calcined at
500 °C for 4 h under N2 flow in order to remove carbonaceous
material which might have been deposited in pores and to further
remove impurities from material. The obtained sample was ground to
200-mesh and then was encoded as ZnO/montmorillonite. X-ray
diffraction (XRD) patterns of powder samples were obtained with a
Shimadzu X6000 diffractometer using Ni-filtered Cu Kα radiation
(λ=1.54 Å) and scanning speed 5°/min DRUV–Vis spectra of the
samples were recorded on a JASCO V-670 spectrophotometer
equipped with a diffuse reflectance accessory; the % R values were
transformed via the Kulbelka–Munk formula. A gas sorption analyzer
(NOVA 1200e) was used to determine the specific surface area and
adsorption–desorption profile using N2 sorbate gas at 196 °C. Elemental
analysis was performed with a Seico EDX. Photo-oxidation was
investigated, with a UV–Visible spectrophotometer (HITACHI U-2080)
and Shimadzu HPLC.
2.1. Photocatalytic activity
Photooxidation reaction ofmethylene blue (MB)was carried out in a
500mL glass beaker in a thermo-controlledwater bath. The beakerwas
charged with 250 mL aqueous solution ofMB at varying concentrations
and 0.2 g/L catalyst. The reactor was equipped with an ultraviolet lamp
at andwas held in a closed box. The radiation sourcewas a Philips 20W
UV-B lamp of placed on top at a distance of 40 cmfromthe glass beaker.
Water from the thermostatic bath was circulated through a reactor
jacket to ensure a constant temperature of 25±0.5 °C inside the reactor.
In order to carry out the experiments under aerobic conditions, the
solution was saturated by bubbling air at atmospheric pressure. H2O2
solution was added into the reactor at a molar ratio of 1:5 (H2O2:MB)
before stirring and photon exposure. The concentration of MB was
determined using a spectrophotometer (UV–Visible HITACHI U-2010)
at 663 nm. HPLC analysis was also employed using a Shimadzu HPLC
with acetonitrile:H2O (50:50) as a mobile flow.