Singlet oxygen-dominated non-radical oxidation in biochar/peroxymonosulfate system for efficient degradation of tetracycline hydrochloride: Surface site and catalytic mechanism

Biochar has attracted much attention in peroxymonosulfate (PMS) activation for the elimination of organic pollutants in water. However, the factor to determine the catalytic efficiency of biochar and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. In this study, Camellia oleifera shell-derived biochar (COSB) was prepared by one-step pyrolysis. The pyrolysis temperature could tune the catalytic performance of COSB. Owing to more C=O groups and defects, the COSB-1000 prepared at 1000 °C showed the optimal activity in PMS activation. In the presence of 0.4 g∙L−1 of COSB-1000 and 1.0 g∙L−1 PMS, 91.57% of tetracycline hydrochloride (TC, 20 mg·L−1) was degraded within 105 min. In addition, the COSB-1000/PMS system demonstrated good anti-interference ability and a wide pH applicability from 3.0 to 11.0. Quenching experiment and electron spin resonance (EPR) spectroscopy suggested that the non-radical oxidation process dominated by the generated 1O2, which was converted from O2•−, play the vital role in TC degradation by the COSB-1000/PMS system. Furthermore, four possible degradation pathways of TC in the COSB-1000/PMS system are proposed by the mass spectroscopy, and the growth-inhibition of Escherichia coli showed that the degradation intermediates were low toxicity. The results here shed light on the generation of 1O2 by biochar and deepen the insight for the environmentally-friendly catalysts derived from biomass in activating PMS for wastewater treatment.