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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]

Fenton oxidation technology is a widely-used advanced oxidation technology. However, the generation of hydroxyl radicals is restrained by the sluggish recovery of Fe(II), thus affecting its long-lasting performance for water decontamination. Here, a novel niobium carbide (Nb 2 C) MXene material was applied as a green co-catalyst. Nb 2 C MXene can significantly promote Fenton reactions to produce hydroxyl radicals for degrading dimethyl phthalate (DMP) with high efficiency and high stability for long-term operation, which outperforms than various reported co-catalysts. Meanwhile, the Nb 2 C/Fe(III)/H 2 O 2 system is capable of non-selectively degrading a wide spectrum of refractory pollutants. Mechanism investigation reveals that Nb 2 C MXene as an electron donor can straight reduce Fe(III), meanwhile mediate electron shuttle from Fe(II) to H 2 O 2 to strongly expedite the generation of hydroxyl radicals. In addition, four main degradation routes of DMP were proposed. Therefore, this study offers an updated and valid strategy for the refractory organic pollutants elimination by coupling Nb 2 C MXene and Fenton oxidation. [Display omitted] • Nb 2 C MXene outperformed than a variety of co-catalysts of enhanced Fenton system. • The Nb 2 C/Fe(III)/H 2 O 2 can non-selectively degrade a wide spectrum of organic contaminants. • Nb 2 C MXene can provide electrons for direct Fe(III) reduction by cleaving Nb-C bonds. • Nb 2 C MXene can mediate electron transfer between Fe(II) and H 2 O 2 to promote Fenton reaction. [ABSTRACT FROM AUTHOR]