Kinetics and Possible Mechanism of the Degradation of Methyl Orange by Microwave Assisted with Fenton Reagent

Abstract

The azo dye model wastewater was treated by microwave assisted with Fenton catalytic wet oxidation, the kinetics of the process and the decolorization mechanism were investigated. The result showed that the reaction of decolorization of methyl orange (MO) by microwave assisted with Fenton reagent followed a pseudo-first-order model. In the treatment process, TN in the solution decreased, and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -N increased, while NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -N and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -N increased first and then decreased. At the end of the process, nitrogen existed mainly in the form of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -N. This indicated that the decreased nitrogen, after a series of reaction with hydroxyl radical (·OH), might be converted to some kind of nitrogen compounds diffusing into the air. The high performance liquid chromatography profiles of MO with different treatment time also confirmed the complete degradation of MO. The conjugated structure and the "benzene-like" structures in MO molecules and its intermediates were broken down step by step.