A highly-efficient peroxymonosulfate activator using a sewage sludge derived biochar supported cobalt oxide: Mechanism and characteristics

The application of biochar derived from sewage sludge (BS) in Fenton-like reactions for contaminant removal has attracted considerable attention. Herein, a BS-supported Co₃O₄ (BS-Co₃O₄) catalyst was synthesized using a simple two-step hydrothermal-calcination process to achieve highly efficient activation of peroxymonosulfate (PMS). The introduction of biochar effectively inhibited the aggregation of Co₃O₄ and reduced cobalt leaching. Compared to Co₃O₄, the mesoporous BS-Co₃O₄ exhibited an 8-fold increase in specific surface area (SSA) to 111.92 m²∙g⁻¹, and a 46 %-66.4 % reduction in crystal plane size. The interaction between biochar and cobalt oxide resulted in several notable enhancements in the BS-Co₃O₄ composite. Specifically, there was an increase in sp² carbon content, a 42.69 % rise in capacitance, and a 79.99 % reduction in charge transfer resistance. These improvements contributed to enhanced PMS activation performance. The BS-Co₃O₄ also contained a higher content of Co(II), sp² carbon, and oxygen vacancies (O_V). Co(II) played a crucial role in the redox reaction, accelerating the formation of SO₄^•− and ¹O₂ during the PMS activation process. Additionally, O_V acted as electron capture centers, further promoting the generation of ¹O₂. Evidence from reactive species investigations and electron paramagnetic resonance (EPR) tests indicated that SO₄^•− and ¹O₂ were the main reactive radicals for eliminating tetracycline (TC). Based on the identification of TC intermediates, two potential degradation pathways were proposed, and a reduction in intermediate toxicity was observed. Experiments involving interference and repetition demonstrated that the BS-Co₃O₄ catalyst was stable and reusable. This work provides a solution with low metal leaching, high recycling performance, and safety for antibiotic wastewater treatment.