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• rGO exhibits excellent performance for enhancing PM oxidation. • Oxygen containing groups can provide electrons for activating PM. • Structural defects can mediate electron transfer between organics and PM. • Changeover between electron donor and mediator can be controlled by regulating active sites. Reports that the exploitation of metal-free carbon materials to enhance permanganate (PM) oxidation to abate organic pollution in water have emerged in recent publications. However, the activation mechanism and active sites involved are ambiguous because of the intricate physicochemical properties of carbon. In this study, reduced graphene oxide (rGO) as a typical carbon material exhibits excellent capability to boost permanganate oxidation for removing a wide array of organic contaminants. The simultaneous two reaction pathways in the rGO/PM system were justified: i) rGO donates to electrons to decompose PM and produce highly reactive intermediate Mn species for oxidizing organic contaminants; ii) rGO mediates electron transfer from organics to PM. Oxygen-containing groups (hydroxyl, carboxyl, and carbonyl) were justified as electron-donating groups, while structural defects (vacancy and edge defects) were shown to be critical for rGO-mediated electron transfer. Therefore, the oxidation pathway of the rGO/PM system can be controlled by regulating oxygen functional groups and structural defects. The changeover from electron donor to electron mediator by decorating surface active sites of carbon materials will be of great help to the design and application of carbocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

• cMnO 2 can significantly promote Fe(VI) to oxidize various micropollutants. • High-valent Fe species were the primary active oxidants in the cMnO 2 −Fe(VI) system. • A novel surface-promoted mechanism was fully verified in the cMnO 2 −Fe(VI) system. • cMnO 2 showed outstanding catalytic stability in actual water. Current research focuses on introducing additional energy or reducing agents to directly accelerate the formation of Fe(IV) and Fe(V) from ferrate (Fe(VI)), thereby ameliorating the oxidation activity of Fe(VI). Interestingly, this study discovers that colloid manganese dioxide (cMnO 2) can remarkably promote Fe(VI) to remove various contaminants via a novel surface-promoted pathway. Many lines of evidence suggest that high-valent Fe species are the primary active oxidants in the cMnO 2 −Fe(VI) system, however, the underlying activation mechanism for the direct reduction of Fe(VI) by cMnO 2 to generate Fe(IV)/Fe(V) is eliminated. Further analysis found that Fe(VI) can combine with the vacancies in cMnO 2 to form precursor complex (cMnO 2 −Fe(VI)*), which possesses a higher oxidation potential than Fe(VI). This makes cMnO 2 −Fe(VI)* is more vigorous to oxidize pollutants with electron-rich moieties through the electron transfer step than alone Fe(VI), resulting in producing Fe(V) and Fe(IV). The products of Fe(VI) decay (i.e., Fe(II), Fe(III), and H 2 O 2) are revealed to play vital roles in further boosting the formation of Fe(IV) and Fe(V). Most importantly, the catalytic stability of cMnO 2 in complicated waters is superior to popular reductants, suggesting its outstanding application potential. Taken together, this work provides a full-scale insight into the surface-promoted mechanism in Fe(VI) oxidation process, thus providing an efficient and green strategy for Fe(VI) activation. [Display omitted] [ABSTRACT FROM AUTHOR]