Metal-Free Activation of Sulfite by Benzoquinone-Derived Carbon for Efficient Organic Contaminant Degradation: Identification and Regulation of Active Sites

Sulfite [S(IV)]-based advanced oxidation processes (AOPs) driven by carbon materials provide an environmentally friendly, economical route for environmental remediation. However, the active sites and involved radical mechanisms are still controversial due to the complexity of the carbon structure, thus greatly hampering the development of highly efficient systems. Herein, a benzoquinone-derived carbon (BQC)/S(IV) system was developed for organic pollutant degradation in an acidic medium for the first time. The quinone groups and conductivity were confirmed as the key factors for S(IV) activation through cyclic voltammetry, antitheses, specific site masking, and quantitative structure-activity relationship methods. Benefiting from the high content of quinone groups and excellent conductivity, the BQC catalyst exhibited much more effective in activating Na2SO3 for organic pollutant degradation compared to most traditional carbon or even metal catalysts. The chronopotentiometry and in situ Raman results revealed that the formation of C-S(IV)* complexes was the primary step to produce SO3 center dot-, followed by the production of SO4 center dot- via a chain reaction, in which the SO4 center dot- radical was responsible for pollutant degradation. The findings may provide novel insights into reaction mechanisms in S(IV)-AOP systems and pave the way toward highly efficient carbon catalysts to activate S(IV) for the elimination of organic contaminants.