Preparation of Biochar-Supported N,S-BiOBr Photocatalytic Material and Optimization of Its Performance for Tetracycline Degradation

Biochar was synthesized through high-temperature pyrolysis, and a biochar-supported nitrogen and sulfur co-doped BiOBr (BC/N,S-BiOBr) photocatalyst was successfully prepared via a one-step solvothermal method, which was applied for the degradation of tetracycline (TC), a widely detected representative antibiotic pollutant, in aqueous solution. This study systematically investigated the effects of catalyst type, initial solution pH, catalyst dosage and initial TC concentration on the photocatalytic degradation process. The experimental results showed that the as-prepared BC/N,S-BiOBr composite exhibited a flower-like nanosphere morphology, characterized by a more complete three-dimensional hierarchical structure, larger specific surface area and suitable optical absorption band, which endowed the composite with significantly improved visible-light absorption capability. Under the optimized reaction conditions (pH = 5, catalyst dosage of 0.7 g/L, initial TC concentration of 10 mg/L), the degradation efficiency of TC over BC/N,S-BiOBr reached 98% after 50 min of visible-light irradiation. In situ electron paramagnetic resonance (EPR) spectroscopy combined with radical quenching experiments confirmed that the modified composite contained abundant oxygen vacancies, and the main reactive species governing TC degradation were identified as photogenerated holes (h+), hydroxyl radicals (·OH) and superoxide radicals (·O2−), with their contribution to TC degradation following the order of h+> ·OH > ·O2−. In summary, by converting municipal sludge into biochar-supported N,S-BiOBr photocatalyst, the modified BC/N,S-BiOBr composite exhibits faster photocatalytic reaction kinetics and higher tetracycline removal efficiency compared with pristine BiOBr, while simultaneously enabling waste resource recovery, solar energy exploitation, and water purification, thereby comprehensively promoting sustainable development in terms of environmental remediation, resource circulation, and low-carbon operation.