Decolorization of methyl orange solution catalyzed by fly ash-H<inf>2</inf>O<inf>2</inf> under microwave irradiation

Abstract

This study explored the potential use of fly ash from coal as a heterogeneous catalyst in the degradation of azo dye by using H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> irradiated by microwave. The effects of various parameters such as fly ash loading, temperature, pH, initial concentration of methyl orange, and dosage of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , 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 H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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% H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , 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 &#60;40% in 4 repeated uses.