Highly efficient degradation of 4-nitrophenol over the catalyst of Mn2O3/AC by microwave catalytic oxidation degradation method

A new microwave catalytic oxidation process based on two kinds of catalysts, the commercially available activated" carbon (AC) and Mn2O3 nanoparticle modified AC (Mn2O3/AC), was reported for the degradation of 4-nitrophenol (4-NP) without adding any oxidant. Effects of microwave power, catalyst dosage, irradiation time, and initial concentration for the degradation efficiency were studied. Results indicated that catalyst of Mn2O3/AC showed much higher catalytic activity than pure AC and Mn2O3 particles. Significantly, 4-NP degradation efficiency reached 99.6%, corresponding to 93.5% TOC removal under optimal conditions with microwave power of 400 W, Mn2O3/AC dosage of 2 g, reaction time of 5 min, and initial concentration of 100 mg/L. Hydroxyl radicals (center dot OH) generated during catalytic reaction is the main oxidant, and O-2 can not effectively improve removal rate. We proposed the microwave 'photoelectric effect' to interpret the generation of center dot OH in view that microwave irradiation can directly excite the catalyst to produce electron-hole pairs and then transform H2O into center dot OH on the surface of catalyst in solution. The obtained kinetic equation for microwave catalytic oxidation degradation of 4-NP was in line with pseudo-first-order kinetic model, that is, apparent rate constant increased as microwave power density increase. (C) 2015 Elsevier B.V. All rights reserved.