Hydrogen peroxide activation by in-situ-loaded CuS/biochar photocatalyst: The critical role of sulfur species in regulating active species

Although metal sulfides have demonstrated exceptional catalytic properties in Fenton-like reactions, little is known about the role of sulfur species in transforming highly active species responsible for degradation organics. CuS (∼12 nm) nano-capsules embedded in the biochar (CuS-BC) were prepared from copper-rich biomass, which could activate H 2 O 2 (4 mM) and completely remove tetracycline (TC) from water within 210 min. Compared with BC/H 2 O 2 /Vis system, the degradation efficiency of TC in the CuS-BC/H 2 O 2 /Vis system was improved by 14.8 times, and the utilization efficiency of H 2 O 2 was improved by 86 times. The whole degradation process of TC can be divided into two stages: quasi-first-order reaction kinetics ( k obs  = 0.015 min −1 ) and zero-order reaction kinetics ( k obs  = 6.457 mol/L/min). Within 90 min, H 2 O 2 is activated to produce hydroxyl radicals ( OH) by surface Cu 2+ on CuS and photogenerated electrons (e − ) generated from CuS photoexcitation, which react immediately with surface SO 3 2− to form SO 4 − . After 90 min, Cu III -peroxo species ( Cu III -O 2 2− -(SO 3 2− ) n ) formed by electron transfer between Cu I , O 2 , and surface SO 3 2− oxidize the remaining 50 % TC through interface interaction. CuS-BC catalyst exhibits excellent photostability and suitability for actual antibiotic wastewater. Overall, this study offers mechanistic insight into the role of sulfur species in the sulfide-based Fenton reactions.