Reducing cobalt leaching in disinfectant degradation: Insights from chitosan-derived carbon encapsulated Co9S8

Cobalt (Co) has significant catalytic activity and is used as an activator of peroxymonosulfate (PMS). However, the practical use of cobalt-based catalysts is hindered by metal leaching and cobalt-induced toxicity. To address these issues, we employed a carbon coating strategy that not only addresses these concerns but also enhances catalytic efficiency by providing additional electrons. In this study, chitosan was utilized for the in situ adsorption of anchored cobalt ions, followed by sulfurization and pyrolysis, to form charcoal-loaded Co9S8 composites (Co9S8/C). Its specific surface area was 79.5 times higher than that of chitosan, and the adsorption rate of PCMX increased by 28.4 %. Within the wide pH range of 3.0 ∼ 11.0, Co9S8/C /PMS system can degrade more than 98 % of PCMX within 5 min, surpassing the combined degradation efficiencies of the CS-C/PMS and Co9S8/C S/PMS systems. The chitosan coating facilitates electron transfer between Co9S8 and PMS, enabling the redox cycle between metal and electrode pairs. Furthermore, in addition to the well-known reactive species SO4·− and ·OH, the presence of Co (IV) adsorbed on the surface of Co9S8/C-1 significantly enhanced PCMX degradation, whereas low-valent sulfur expedited the rate-limiting process of Co3+ reduction to Co2+. The Co9S8/C/PMS system also demonstrated high efficiency in treating other representative emerging pollutants such as sulfadiazine, phenol, bisphenol A, and sulfonamide. The chitosan-derived carbon coating strategy presented in this study provides a robust theoretical foundation for the practical application of cobalt-based catalysts, offering promising solutions to the urgent environmental challenges.