Phenol degradation catalyzed by metal oxide supported porous carbon matrix under UV irradiation

Abstract

Refinery wastewater contains light fractions of aliphatic and aromatic petroleum hydrocarbons such as phenol, which demands removal to acceptable levels before being discharged into water bodies. Literature based screening of various metal-oxide catalysts for phenol degradation indicated oxides of titanium and zinc to be the most effective catalysts. TiO2/Activated carbon (AC) and ZnO/AC catalysts were synthesized via hydrothermal methods and tested for phenol degradation. Physicochemical characterization of the synthesized catalyst revealed evenly distributed nano-sized titanium dioxide and well crystalized ZnO structure on the carbon surface. While the composite synthesis process reduced the overall BET surface area of both ZnO/AC and TiO2/AC, it retained the major surface functional groups of AC with addition to metal oxides in the porous complex. Synthesized ZnO/AC and TiO2/AC showed improved phenol degradation efficiency than pure activated carbon under UV light illumination. Effect of various process parameters such as illumination duration, catalyst dosage, and initial concentration of phenol were assessed to identify optimal conditions for maximum degradation. Further, kinetic data were generated and the results were validated using reaction models to evaluate the degradation mechanism. At lower concentrations, the kinetic parameters matched well with the first order reaction model while at higher concentrations, it followed second order kinetics owing to the shift in the mechanism of adsorption. The relatively enhanced phenol degradation efficiency by ZnO/AC over TiO2/AC composite could be attributed to the synergetic effect of adsorption and photocatalytic degradation. `