Combination of adsorption, photochemical and photocatalytic degradation of phenol solution over supported zinc oxide: Effects of support and sulphate oxidant

SiO2, ZSM-5 and MCM-22 supported ZnO catalysts were prepared. Elemental analysis and Zn element mapping were conducted to evaluate the dispersion of ZnO on the supports. The prepared materials were tested in adsorption, photochemical oxidation, and photocatalytic degradation of phenol in aqueous solution. Peroxydisulphate (PDS) and peroxymonosulphate (PMS) were used as oxidants to provide sulphate radicals for chemical oxidation. It was found that adsorptive property of the supports played an important role in photochemical and photocatalytic oxidation. MCM-22 was found to exhibit stronger adsorption, giving 68% of phenol removal in 25 ppm solution, compared to 0%, 3%, and 4% removal on ZnO, SiO2, and ZSM-5, respectively. The PDS and PMS oxidants could be activated by low intensity UV at wavelength greater than 380 nm. However, under low UV intensity, SiO2 and ZSM-5 supported ZnO did not exhibit synergistic effect for phenol degradation. The phenol removal efficiencies in PDS/UV, ZnO/PDS, ZnO/UV, ZnO(10%)/MCM-22/UV/PDS, and ZnO(10%)/MCM-22/UV/PMS at 90 min and 60 μW/cm2 were 34.2, 13.8, 14.2, 79.0, and 72.1%, respectively. The apparent reaction rate constants of PDS/UV, ZnO/PDS, ZnO/UV, ZnO(10%)/MCM-22/UV/PDS, and ZnO(10%)/MCM-22/UV/PMS were 0.00473, 0.00154, 0.00262, 0.00831, and 0.00365 min−1, respectively.