Decolorization of methyl orange solution catalyzed by fly ash-H2O2 under microwave irradiation

This study explored the potential use of fly ash from coal as a heterogeneous catalyst in the degradation of azo dye by using H2O2 irradiated by microwave. The effects of various parameters such as fly ash loading, temperature, pH, initial concentration of methyl orange, and dosage of H2O2, and deactivation of catalytic effect of fly ash were studied. The metal oxide compounds in fly ash, such as iron and manganese, can combine with H2O2 to form a Fenton-like reagent and produce hydroxyl radical, which can oxidize persistent organic pollutants into small molecule compounds. Under microwave irradiation, methyl orange (MO) solution, a typical azo dyestuff selected as a model pollutant, was decolorized. For the 100mL 1000mg/L MO solution, the decolorization and COD removal ratios were 99.8% and 80%, respectively, with a pH of 2, 2 grams of fly ash, 1 mL of 30% H2O2, 800 W of microwave power, and an irradiation time of 5 minutes. The negligible homogeneous catalytic action of trace metals leached from the fly ash such as Fe, Mn, and Cu, confirmed the sole heterogeneous catalytic nature of fly ash particles in the cleavage of azo bonds. Fly ash deactivation was found to be <40% in 4 repeated uses.