New insights into peroxydisulfate activation by nanostructured and bulky carbons

Carbon-driven persulfate activation processes have attracted considerable attention because of their metal-free feature. However, the underlying mechanisms are not fully understood. In the study, biochar (WBC), activated carbon (PAC), carbon nanotube (CNT) and graphene nanoplatelet (GNP) were used as the activators of peroxydisulfate (PDS). Efficient removal of 4-chlorophenol (4-CP) was observed in the PAC/PDS, CNT/PDS and GNP/PDS systems. PAC performed better than CNT and GNP in both adsorption and activation. These three systems had identical reaction products and similar responses to the variation of reaction conditions, e.g., pH, concentrations of chloride and humic acid, indicated that the same mechanisms existed in them. The transformation of 4-CP went through two reaction pathways: direct oxidation by non-radical reactive species and carbon-mediated electron transfer. 4-CP molecules could be degraded or combined with each other to form dimers and trimers. These results provide a novel understanding of carbon-driven persulfate systems.