The residual of oxidant chemicals in advanced oxidation processes (AOPs) resulted in both economic cost and secondary pollution. Herein, we report a direct oxidation of phenolic pollutants induced by Ca-Mn-O perovskites without using an oxidant. Governed by one-electron transfer process (ETP) from the phenolics to the Ca-Mn-O perovskites, this direct oxidation proceeds in fast reaction kinetics with activation energy of 51.4 kJ/mol, which was comparable with those AOPs-based catalytic systems. Additionally, mineralization and polymerization reactions occurred on the Ca-Mn-O surface and ensured the complete removal of phenolics. The high spin state Mn(III) within Ca-Mn-O structure was the dominant active site for this ETP. The elongated axial Mn(III)–O bonds within the [MnO₆] octahedron facilitated the acceptance of the electrons from the phenolics and thus promoted the initiation of the direct oxidation process. Mn(III) in the high spin state can also activate dissolved O₂ to produce singlet oxygen (¹O₂) for a fast removal of phenolics. The mixed Mn(III)/Mn(IV) within Ca-Mn-O accelerated the ETP by enhancing the electrical conductivity. This efficient Ca-Mn-O-induced ETP for removal of organic contaminants casts off the dependence on external chemical and energy inputs and provides a sustainable approach for transforming the toxic organic pollutants into value-added polymers.

Two−dimensional (2D) supports confined single−atom catalysts (2D SACs) with unique geometric and electronic structures have been attractive candidates in different catalytic applications, such as energy conversion and storage, value−added chemical synthesis and environmental remediation. However, their environmental applications lack of a comprehensive summary and in−depth discussion. In this review, recent progresses in synthesis routes and advanced characterization techniques for 2D SACs are introduced, and a comprehensive discussion on their applications in environmental remediation is presented. Generally, 2D SACs can be effective in catalytic elimination of aqueous and gaseous pollutants via radical or non−radical routes and transformation of toxic pollutants into less poisonous species or highly value−added products, opening a new horizon for the contaminant treatment. In addition, in−depth reaction mechanisms and potential pathways are systematically discussed, and the relationship between the structure−performance is highlighted. Finally, several critical challenges within this field are presented, and possible directions for further explorations of 2D SACs in environmental remediation are suggested. Although the research of 2D SACs in the environmental application is still in its infancy, this review will provide a timely summary on the emerging field, and would stimulate tremendous interest for designing more attractive 2D SACs and promoting their wide applications.

Photocatalytic hydrogen evolution reaction (PC-HER) provides a solution to energy crisis and environmental pollution. Herein, different graphitic carbon nitride (g-C₃N₄)-based van der Waals (vdW) type II homojunctions have been fabricated and g-C₃N₄/K-doped g-C₃N₄ nanosheets have an outstanding PC-HER rate of 1,243 μmol·h⁻¹·g⁻¹ under visible light, higher than that of bulk g-C₃N₄, doped g-C₃N₄ nanosheets, and mixed nanosheets. The enhanced PC-HER performance can be ascribed to the cooperative effects of the shortened bandgap, enlarged specific surface area, matched type II energy band structure, “face to face” vdW charge interaction, and peculiarly partite positions of the conduction and valence bands in different layers. Besides, the type II junctions were found superior to binary type II junction. This study highlights the synergistic effect of different strategies in improving the PC-HER capacities of g-C₃N₄, especially the application of particular vdW junctions, and provides new insights to the structures and mechanism.