Tetracycline degradation by peroxydisulfate activated with the composite material of biochar and cobalt-modified carbon nitride: Efficiency, stability, and degradation pathway

In recent years, non-homogeneous peroxydisulfate (PDS) activation for organic pollutant degradation has gained interest. Nonetheless, PDS activation using transition metal and carbon catalysts faces challenges such as metal leaching and inadequate catalytic performance. Herein, biochar-loaded cobalt-modified carbon nitride composite material (BC@CN-Co) was synthesized and employed as an activator for PDS activation. The outcomes suggested that the degradation efficiency of tetracycline (TC) could reach 82% within 360 min under the optimized condition (TC = 5 mg/L, BC@CN-Co = 1 g/L, PDS = 2 mM, nature pH, T = 25℃), with corresponding apparent rate constant (Kobs) of 0.00375 min-1, which was approximately 5.5 and 2.0 times that of the biochar/PDS (0.00068 min-1) and cobalt-modified carbon nitride/PDS (0.00178 min-1) systems, respectively. BC@CN-Co exhibits excellent degradation of TC within a pH range of 3~7, with Cl-, NO3-, H2PO4-, and HA having little effect on TC degradation. Mechanistic experiments confirmed that the non-radical pathway mediated by singlet oxygen (1O2) and electron transfer plays an important role in TC degradation in the BC@CN-Co/PDS system. Furthermore, BC@CN-Co could efficiently reduce the leaching of Co ions to prevent metal pollution. This study provides an alternative PDS activator for the degradation of antibiotics in wastewater.