Microwave Catalyzed Oxidative Degradation of Methyl Orange in Simulated Wastewater Using Microwave Catalytic TiO2/AC and Mechanistic Studies

Simulated wastewater containing methyl orange (MO C14H14N3NaO3S) was treated using a microwave (MW)-catalyzed reaction oxidative degradation (MCROD) method using MW catalyst TiO2/AC without H2O2, O2 or other oxidants. The effects of the MW power, irradiation time, catalyst loading and initial MO concentration were investigated regarding the degradation rate of MO. The degradation rate increased when increasing the MW power, irradiation time, and catalyst loading and decreased when increasing the initial MO concentration. For the simulated wastewater with an initial concentration of 100 mg/L MO, the degradation rate was 99.2% at a MW power of 600 W over 12 minutes with 22 g/L of TiO2/AC. This study explored the mechanism for the MCROD of MO: the formation of hydroxyl radicals (•OH) catalyzed by MW and the oxidative degradation of MO by the •OH in an aqueous solution. A detailed mechanism was also proposed. Studying the dynamics of the reaction revealed that the oxidation reaction was first-order.