Heteroatom doping in metal-free carbonaceous materials for the enhancement of persulfate activation

Metal-free carbonaceous materials emerge as a rising star of catalysts in the persulfate-based advanced oxidation processes (PS-AOPs) for green remediation. Appropriate heteroatom doping into metal-free carbonaceous materials is an effective way to improve PS activation performance. However, the relationship between doped heteroatoms and enhanced catalytic activity is still ambiguous. Herein, we aim to tease out the contribution of doped heteroatoms to the improvement of PS activation. In this review, the common preparation methods of heteroatom-doped metal-free carbonaceous materials are introduced and classified into direct synthesis and post treatment. Then, some important characterization techniques of these materials are presented from the aspects of morphology, elemental composition, structure, and surface chemical analysis. What’s more, the performance improvement and mechanism exploration of metal-free carbonaceous materials caused by heteroatom doping in PS activation are comprehensively analyzed. Concretely, heteroatoms are imbedded into carbon materials in the form of different bond configurations and enhance PS activation by reinforcing radical and/or non-radical pathways. Hence, different catalytic mechanisms initiated by diverse heteroatom bond configurations, and their contribution to radical and non-radical pathways are discussed. The insight into the mechanism of PS activation enhanced by heteroatom doping can guide the directional synthesis of metal-free carbonaceous materials to realize better practical applications.