A synergistic Co3O4 nanoparticles and nitrogen-doped biochar composite for efficient peroxymonosulfate activation toward degradation of multiple antibiotic pollutants

Abstract

A nitrogen-doped biochar loaded with Co₃O₄ nanoparticles (Co–NBC-550) was developed to activate peroxymonosulfate (PMS) for antibiotic degradation in water. Tetracycline (TC, 20 mg L⁻¹) was used as a model pollutant. Under pH 6.12 with PMS = 0.2 g L⁻¹ and Co–NBC-550 = 0.2 g L⁻¹, the Co–NBC-550/PMS system achieved 98% removal in 7 min (k_obs = 0.52 min⁻¹), 5.7× that of NBC/PMS. Characterization showed uniformly dispersed Co₃O₄ and a mesoporous framework with abundant active sites, together with enriched oxygen vacancies (V_O) at the Co–O–C interface that facilitated PMS adsorption/activation. Reactive oxygen species (SO₄˙⁻, ˙OH, and ¹O₂) played vital roles, with ¹O₂ dominating the non-radical pathway. XPS confirmed the Co²⁺/Co³⁺ redox cycle, while pyridinic-N, graphitic-N, and CO groups enhanced activity. Broad-spectrum performance was also observed: 93.12% removal of ofloxacin, 87.13% of sulfamethoxazole, and complete phenol removal within 7 min. LC-MS identified key intermediates and pathways; toxicity predictions (TEST) showed lower acute toxicity and bioaccumulation of products. Reusability (5 cycles) and continuous-flow operation (600 min) confirmed stable performance. These results highlight Co–NBC-550 as an efficient and practical PMS catalyst for antibiotic-contaminated waters, with TC as a mechanistic model.