Xiaoping Li

Fenton process and activated carbon are widely used for water treatment, yet both encounter significant challenges, such as slow Fe³⁺/Fe²⁺ conversion and rapid adsorbent saturation. Herein, a category of hitherto overlooked dynamic single-atom sites on heteroatom-doped carbons (HDCs) that mitigate the above problems was observed by coupling Fenton and activated carbon. Specifically, the defects on the carbon surface, particularly the heteroatom defects, coordinated with Fe³⁺ in the bulk solution to form dynamic single-atom sites that simultaneously suppress the Fe³⁺ hydrolysis and promote the Fe³⁺/Fe²⁺ conversion. This synergy sustains the efficient oxidation process of the coupled system through up to 5 cycles due to the optimized Fe³⁺/Fe²⁺ cycling. Moreover, dynamic single-atom sites enable the continuous removal of adsorbates from the carbon surface, extending the time before adsorption saturation and maintaining nearly 100% efficiency for 480 h. Mechanistic analysis revealed that dynamic single-atom sites optimize the Fe³⁺/Fe²⁺ redox cycle through forming a carbon → ligand atoms → Fe ↔ H₂O₂ electron flux pathway. Their bidirectional electron flux with H₂O₂ enhances OH· production, thereby improving the Fenton oxidation process. These findings offer crucial insights for overcoming challenges in environmental engineering technologies and underscore the potential superiority of coupled systems in practical applications.

Precious metals exhibit promising potential for the hydrogen evolution reaction (HER), but their limited abundance restricts widespread utilization. Loading precious metal nanoparticles (NPs) on 2D/2D heterojunctions has garnered considerable interest since it saves precious metal consumption and facilitates unidirectional electron transmission from semiconductors to active sites. In this study, Ru NPs loaded on MXenes Mo₂C by an in-site simple strategy and then formed 2D/2D heterojunctions with 2D g-C₃N₄ (CN) via electrostatic self-assembly were used to enhance photocatalytic H₂ evolution. Evident from energy band structure analyses such as UV-vis and TRPL, trace amounts of Ru NPs as active sites significantly improve the efficiency of the hydrogen evolution reaction. More interestingly, MXene Mo₂C, as substrates for supporting Ru NPs, enriches photoexcited electrons from CN, thereby enhancing the unidirectional electron transmission. As a result, the combination of Ru-Mo₂C and CN constructs a composite heterojunction (Ru-Mo₂C@CN) that shows an improved H₂ production rate at 1776.4 μmol∙g⁻¹∙h⁻¹ (AQE 3.58% at 400 nm), which is facilitated by the unidirectional photogenerated electron transmission from the valence band on CN to the active sites on Ru (CN→Mo₂C→Ru). The study offers fresh perspectives on accelerated unidirectional photogenerated electron transmission and saved precious metal usage in photocatalytic systems.