Advances and prospects of metal-free carbon materials for persulfate-based advanced oxidation processes in aquatic pollutant removal

Nowadays, persulfate-based advanced oxidation processes (PS-AOPs) are flourishing promptly owing to their promising potential in eliminating refractor contaminants. As the novel and high-activity catalysts, metal-free carbon materials (CMs) are extensively used in clean energy production, environment remediation, medicine, as well as other fields because of their higher specific area, abundant surface functional groups, excellent structural adjustability, good biocompatibility, environmentally friendly, and facile fabrication. These remarkable physicochemical characteristics may guarantee CMs-based materials to be hopeful catalysis in PS-AOPs. In this work, we make a comprehensive review of CMs-based materials in PS-AOPs from different aspects, including categories, catalytic process mechanism, and tailoring strategy for enhancing catalytic activity of CMs as well as the microstructure-performance relationship of the CMs. First of all, we discuss the different categories, characteristic, and application of CMs. Secondly, the possible catalytic mechanism of persulfate activation (including radical pathway, non-radical pathway, and the combined radical and non-radical pathway) by CMs-based catalysts were introduced. In addition, in order to further enhance their catalytic activity and assess environmental impact of CMs-based catalysts, some promising tailoring strategy and environmental impact assessment methods were summarized and put forward accordingly. Finally, challenges as well as future prospects of CMs-based materials in environment remediation were mentioned. Overall, this account will certainly help to reveal the mist of CMs in PS-AOPs and give some reference to facilitate the further development of the CMs/PS-AOPs systems in wastewater pollution purification, and bring out some multidisciplinary afflatus for CMs applications.