Microwave-enhanced catalytic wet peroxide oxidation of quinoline: the influence of pH and H2O2 dosage and identification of reactive oxygen species

Abstract

This article presents a comprehensive study about the influence of initial pH and H₂O₂ dosage on quinoline mineralization efficiency (denoted by TOC abatement) by microwave-catalytic wet peroxide oxidation (MW-CWPO) with supported Cu–Ni bimetallic oxides as a catalyst and reactive oxygen identification on the basis of inhibition of quinoline mineralization using the specific radical scavengers. In an initial pH range from 2.0 to 8.0, this MW-CWPO was powerful, with the reaction at pH 7.0 obtaining the highest 81.12% TOC abatement under MW 500 W, H₂O₂ 22.75 mmol L⁻¹, Cu/Ni-catalyst 4 g L⁻¹, and T 333 K. Five carboxylic acids, namely acetic acid, formic acid, succinic acid, oxalic acid, and glycolic acid, were quantified to elucidate the pH fall during mineralization under alkaline and neutral conditions. The experiments of reactive oxygen identification on the basis of inhibition of quinoline mineralization under the corresponding scavenger for ˙OH and O₂˙⁻ exhibited ˙OH and O₂˙⁻ immersed in supported bimetallic Cu/Ni oxides catalyzing MW-CWPO, and that ˙OH was a direct product and O₂˙⁻ was a secondary oxidant produced from ˙OH-involved reactions. Based on the results of stability and metal leaching experiments, it could be concluded that supported Cu–Ni bimetallic oxides could be a proper catalyst.