Coupling of sulfur and boron in carbonaceous material to strengthen persulfate activation for antibiotic degradation: Active sites, mechanism, and toxicity assessment

Abstract

Carbon-mediated persulfate advanced oxidation processes (PS-AOPs) are appealing in contaminant remediation. For the first time, S,B-co-doped carbon-based persulfate activators were synthesized through direct carbonization of sodium lignosulfonate and boric acid. By degrading sulfamethoxazole (SMX), CSB-750 obtained 98.7% removal and 81.4% mineralization within 30 min. In comparison with solo S or B doping, S and B co-doped carbon showed the coupling effect for enhanced catalysis. The rate constant (kobs) of 0.1679 min–1 was 22.38- and 279.83-fold higher than those of CS-750 (0.0075 min–1) and CB-750 (0.0006 min–1), respectively. The degradation was efficient at strong acidic and weak basic conditions (pH 3–9). Substantial inhibition effect was presented at strong basic condition (pH 10.95) and in presence of CO32–. The CO32–-caused inhibition was the combined result of the cooperation of pH and quenching O2·–. Thiophene sulfur, BC3, BC2O, and structural defects were identified as the active sites for PS activation. Radical and nonradical pathways were both involved in the CSB-750/PS/SMX system, where 1O2 dominated the degradation, SO4·–, ·OH and direct electron transfer played the subordinate role, and O2·– served as a precursor for the formation of partial 1O2. The toxicity of degradation system, the effect of real water matrix, and the reusability of carbocatalysts were comprehensively analyzed. Nine possible degradation pathways were proposed. This work focuses on the catalytic performance improvement through the coupling effect of S,B co-doping, and develops an advanced heteroatom doping system to fabricate carbonaceous persulfate activators.