Photodegradation of volatile organic compounds catalyzed by MCr–LDHs and hybrid MO@MCr–LDHs (M=Co, Ni, Cu, Zn): The comparison of activity, kinetics and photocatalytic mechanism
Efficient removal of high–concentration volatile organic compounds (VOCs) has been a challenging task. Here, four types of organic–inorganic hybrid layered double hydroxides (MO@MCr–LDHs, M=Co, Ni, Cu, Zn) were synthesized and used for highly efficient photodegradation of p–xylene under visible–light irradiation. Reactivity of the 4 hybrid MO@MCr–LDHs was found in the following general order, CuO@CuCr–LDHs > ZnO@ZnCr–LDHs > NiO@NiCr–LDHs > CoO@CoCr–LDHs. Under optimized reaction condition (2.0 g catalyst dosage, 500 W, 50% relative humidity, 40 oC), >87 % of p–xylene was removed by hybrid CuO@CuCr–LDHs after 180 min reaction (from 175 mg/m3 to 22.6 mg/m3), triples the reactivity of MCr–LDHs. By comparing the physiochemical structures of the catalysts, we found that the hybridization of MO and MCr narrows the band gap (from 2.84 to 2.29 eV), increases the specific surface area (from 69.5 m2/g to 139.1 m2/g) of LDHs, and enhances the photocatalytic property for VOCs degradation (including benzene, toluene, o–xylene, and m–xylene), leading to more efficient generation of reactive species, decreasing the apparent activation energy, improving the electrochemical property, and possibly changing the reaction intermediates and pathways.