Activation of peroxymonosulfate by biochar-based catalysts and applications in the degradation of organic contaminants: A review

Sulfate radical-based advanced oxidation processes (SR-AOPs) have received intensively attention due to the ability and adaptability. Biochar-based catalysts have been regarded as the effective catalysts for activating peroxymonosulfate (PMS) to generate sulfate radicals (SO4•-). This article discussed the advance of the PMS activation by biochar-based catalysts. Firstly, the sources and synthesis methods of biochar-based catalysts have been discussed. Secondly, the different activation mechanisms (including radical pathways and non-radical pathways) of pristine biochar, heteroatom doping biochar and biochar composites catalysts for PMS activation are reviewed, respectively, which includes (i) the significant role of persistent radical (PFRs) and the special structures (defects and graphitization) of pristine biochar, (ii) the effects of element doping (especially N atom) and metal species on the biochar catalysts, (iii) the production mechanisms of reactive oxygen species (ROS) and special non-radical mechanism. Thirdly, the influences of PMS and catalysts concentration, temperature, pH, anions and natural organic matter (NOM) on the contaminants degradation process have been presented. Finally, the conclusion and prospects section discussed the challenges and possible future directions for the degradation of contaminants by biochar/PMS systems. This review is expected to provide new ideas for the application of biochar-based catalysts and broaden the ways for the removal of organic contaminants.