Highly Efficient and Selective Hg(II) Removal from Water Using Multilayered Ti₃C₂Ox MXene via Adsorption Coupled with Catalytic Reduction Mechanism

Mercury (Hg) removal is crucial to the safety of water resources, yet it lacks an effective removal technology, especially for emergency on-site remediation. Herein, multilayered oxygen-functionalized Ti 3 C 2 (Ti 3 C 2 O x ) (abbreviated as M-Ti 3 C 2 ) nanosheets were prepared to remove Hg(II) from water. The M-Ti 3 C 2 has demonstrated ultrafast adsorption kinetics (the concentration decreased from 10 400 to 33 μg L –1 in 10 s), impressively high capacity (4806 mg g –1 ), high selectivity, and broad working pH range (3–12). The density functional theory (DFT) calculations and experimental characterizations unveil that this exceptional Hg(II) removal is owing to the distinct interaction ( e.g ., adsorption coupled with catalytic reduction). Specifically, Ti atoms on the {001} facets of M-Ti 3 C 2 prefer to adsorb Hg(II) in the form of HgClOH, which subsequently undergoes homolytic cleavage to form radical species ( e.g ., • OH and • HgCl). Immediately, the • HgCl radicals dimerize and form crystalline Hg 2 Cl 2 on the edges of M-Ti 3 C 2 . Up to ∼95% of dimeric Hg 2 Cl 2 can be efficiently recovered via facile thermal treatment. Notably, owing to the adsorbed • OH and energy released during the distinct interaction, M-Ti 3 C 2 has been oxidized to TiO 2 /C nanocomposites. And the TiO 2 /C nanocomposites have shown to have better performance on the photocatalytic degradation of organic pollutants than Degussa P25. These exceptional features coupled with mercuric recyclable nature make M-Ti 3 C 2 an outstanding candidate for rapid/urgent Hg(II) removal and recovery.