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

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 (SO(4)(-)and OH). KOH activation further promotes the generation of the two radical species and further involves superoxide ion radicals (O-2(-)), thus achieving deeper mineralization of the organic pollutants. Different from the nonradical species confined on the catalyst surface, radical oxidation (including the singlet oxygen (O-1(2)) transformed from O-2(-)) 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.