Fine-Tuning Radical/Nonradical Pathways on Graphene by Porous Engineering and Doping Strategies

Abstract

Nitrogen and sulfur co-doped graphene (N,S-G) is activated using ZnCl2, KOH, and CO2 to develop different defects and functionalities. The modified carbo-catalysts are used to activate peroxymonosulfate (PMS) for phenol degradation. Compared with nitrogen-doped graphene (N-G), N,S-G exhibits better catalytic activity, and KOH activation further enhances the oxidation efficiency. Radical quenching experiments, electrochemical characterization, and electron paramagnetic resonance characterization reveal that N-G activates PMS via a nonradical pathway. The involvement of a secondary sulfur dopant will transform the reaction pathway into radical-dominated oxidation (SO4•–and •OH). KOH activation further promotes the generation of the two radical species and further involves superoxide ion radicals (O2•–), thus achieving deeper mineralization of the organic pollutants. Different from the nonradical species confined on the catalyst surface, radical oxidation (including the singlet oxygen (1O2) transformed from O2•–) occurs in bulk solution and protects the carbo-catalyst from corrosion, herein securing better structural integrity and stability of carbo-catalysts. Based on the structure–activity features, we designed a high-performance scalable carbo-catalyst of KOH-activated and N,S-codoped graphene (N,S-G-rGO-KOH) using a facile strategy, which is promising for practical applications.