Insight into the oxidation of phenolic pollutants by enhanced permanganate with biochar: The role of high-valent manganese intermediate species

This work demonstrated that the oxidation of phenolic pollutants by permanganate (KMnO₄) was effectively enhanced by a commercial biochar. Detailed characterization data indicated that the biochar contains porous structures, amounts of defective sites and abundant redox-active groups. In the presence of biochar, the degradation efficiency of 4-nitrophenol by KMnO₄ surged from 5% to 92% in 180 min, up to 37.8% of total organic carbon (TOC) was removed. Meanwhile, acute toxicity of 4-nitrophenol was greatly reduced. Through analyzing oxidation products of triclosan (TCS) and using methyl phenyl sulfoxide (PMSO) as a chemical probe, high-valent Mn intermediates (i.e. Mn(VI)/Mn(V)) were proved to be the dominant oxidant in the KMnO₄/biochar system. Quantitative structure-activity relationships (QSARs) were established between oxidation rate constants of various substituted phenols and classical descriptor variables (i.e., Hammett constant σ⁺). KMnO₄/biochar was found to be less selective to the substituent variation of phenolic compounds compared with O₃, K₂FeO₄, ClO₂ and persulfate/carbon nanotube (PDS/CNT). This work provided a novel catalytic oxidation technology for eliminating phenolic compounds, and improved insights into the mechanistic study of the KMnO₄-based oxidation process.