Semi-quantitative probing of reactive oxygen species in persulfate-based heterogeneous catalytic oxidation systems for elucidating the reaction mechanism

Persulfate-based heterogeneous catalytic oxidation systems have attracted increasing interests in water pollution control field. Sulfate/hydroxyl radical, singlet oxygen, and catalyst-mediated electron transfer are commonly recognized to be responsible for the organic pollutant removal. However, reliable quantitative methods for detecting reactive oxygen species (ROS) are still lacking to clarify their contribution to the reaction mechanism. In this work, a soluble probe, 9,10-Anthracenediyl-bis (methylene)-dimalonic acid, which is sensitive to both sulfate/hydroxyl radical and singlet oxygen, was developed to semi-quantify the ROS in persulfate-based catalytic oxidation systems. The detection results reveal the predominant catalyst-mediated electron transfer mechanism, rather than the ROS mechanism, and its universality in several representative heterogeneous catalytic systems (i.e., FeMnO, CNT, Mn3O4, and biochar catalyzing peroxymonosulfate and peroxydisulfate for organic pollutant degradation). Compared with the electron paramagnetic resonance detection with DMPO and TEMP as spin-trapping agents and quenching effects of ROS by alcohol, furfuryl alcohol, and L-histidine, such a semi-quantitative detection method exhibits simplicity and improved reliability in mechanism elucidation. This semi-quantitative method plays a vital role in clarifying the reaction mechanism in persulfate-based heterogeneous catalytic oxidation systems, which might open a door for the optimization and regulation of catalytic oxidation water purification technology.