Recent advances in design and engineering of MXene-based catalysts for photocatalysis and persulfate-based advanced oxidation processes: A state-of-the-art review

There is a growing concern about wastewater treatment due to the presence of various stubborn pollutants that require advanced catalysts and techniques for effective treatment. As two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, MXene is considered a promising candidate for environmental applications owing to outstanding characteristics, including high surface area, hydrophilic surface, structural flexibility, and surface tunable chemistry. This review consolidates the recent advancements in the utilization of MXenes in photocatalysis and persulfate-based advanced oxidation processes (PS-AOPs) for the abatement of various pollutants from water and wastewater. The fundamentals and synthesis techniques for the MXene and MXene-based catalysts are summarized. Furthermore, strategies to boost the photocatalytic efficiency of MXene-based catalysts, catalytic degradation performance, and reaction mechanisms for organic pollutants removal by inducing binary/multicomponent heterojunctions, S-scheme/Z-scheme, metal/non-metal doping, and defects/vacancies engineering are emphasized in detail. It also offers new perspectives on the single-use of MXene, the MXene reducibility, MXene as support and co-catalyst for persulfate activation, and photocatalytic activated persulfate by MXene-based catalysts and the corresponding mechanisms are elucidated. Applications of MXene-based processes for real matrices, toxicity assessment, and MXene stability for pollutants removal are highlighted. Finally, the review focuses on the conclusions, challenges, and opportunities of MXene-based catalysts in environmental applications to attain high catalytic efficiency. This review provides enlightening knowledge into the utilization of MXene-based catalysts in the field of photocatalysis and PS-AOPs.