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

Abstract

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 (OV). Co(II) played a crucial role in the redox reaction, accelerating the formation of SO4•− and 1O2 during the PMS activation process. Additionally, OV 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.