Review on carbonaceous materials as persulfate activators: Structure performance relationship, mechanism and future perspectives in water treatment

Recently, carbonaceous materials have attracted increasing attention in advanced oxidation processes (AOPs) due to their capability, adaptability and efficiency in the degradation of organic wastewater contaminants with little or no leaching potential. Previous reviews have raised serious controversies regarding the occurrence and mechanism of the persulfate activation process but the detailed influence of the structural features on the persulfate activation performance is yet to be analyzed. This state-of-the-art review aims to discuss the recent structural adjustments, modifications and modulation of carbonaceous materials in relation to how they affect the persulfate activation performance. It was observed that tweaking the carbon structural features (such as the crystal structure and defects, the porous structure, surface area, pore size, and oxygen-containing groups) influences the reaction mechanism, further controlling the persulfate activation process. Hence, different reaction mechanisms involved in the carbon-based persulfate activation process were discussed. Also, the influence of the reaction pathway on the nature of the degradation or intermediate products was examined along with some real water investigations. Environmental application of carbon-based persulfate systems was discussed in relation to its influence on several background ions like Cl−, HCO3−, CO32−, NO3−, SO42−, H2PO4−, natural organic matter (NOM) and humic acid. Furthermore, future research directions for improving the design and properties of carbonaceous catalysts were proposed.