Oxidation products and degradation pathways of 4-chlorophenol by catalytic ozonation with MnOx/γ-Al₂O₃/TiO₂ as catalyst in aqueous solution

To identify the intermediates of 4-chlorophenol (4-CP) and bring forward the degradation pathways in the process of catalytic ozonation of 4-CP, 4-CP was ozonated with MnOx/γ-Al₂O₃/TiO₂ (MAT) catalyst, and 4-CP was almost decomposed within 30 min, the mineralization reaching above 94.1% at 100 min. The evident reduction of the degradation with the addition of the radical scavenger tert-butanol (TBA) and the stronger spin-adduct signals of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) indicated that 4-CP was oxidized primarily by hydroxyl radical (·OH). Analysis of GC-MS, HPLC and IC confirmed that aromatic compounds and carboxylic acids were predominant oxidative organic intermediates of 4-CP in catalytic ozonation. The main degradation steps were hydroxylation of 4-CP and the formation of hydroquinone, 4-chlororesorcinol and 4-chlorocatechol. The low molecular weight (LMW) acids, such as malic, malonic, oxalic, acetic, and formic acid, were formed from the further oxidation of the intermediates.