Mechanistic pathways and optimization of salinity-tolerant antibiotic degradation catalyzed by Gracilaria verrucosa biochar

Tetracycline (TC), a commonly found antibiotic, poses ecological risks when present in aquatic environments. A low-cost activated biochar was developed from Gracilaria verrucosa (GBVC) via one-step pyrolysis (800 °C) and utilized to activate peroxydisulfate (PDS) for TC degradation. Under optimized conditions, GVBC₈₀₀ achieved 100 % of TC degradation (TC = 10 mg L⁻¹, GVBC₈₀₀ = 100 mg L⁻¹, PDS = 1.25 mM, pH 5.0), with adaptability across a wide range of pH (3.0–11.0). TC degradation involved radical (^•OH and SO₄^•−) and non-radical (¹O₂) pathways, as well as electron transfer, facilitated by pyridinic N, thiophene sulfur (S 2p_3/2), and structural defects in GVBC₈₀₀. In saline water, nearly 100 % TC removal was achieved using 2.5 mM of PDS and 200 mg L^–1 of GVBC₈₀₀. Degradation pathways were proposed and TC mineralization was evaluated, highlighting the efficacy of the GVBC₈₀₀/PDS system for TC degradation in challenging environmental conditions.