Highly Efficient and Selective Hg(II) Removal from Water Using Multilayered Ti₃C₂O MXene via Adsorption Coupled with...

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 Ti₃C₂ (Ti₃C₂O) (abbreviated as M-Ti₃C₂) nanosheets were prepared to remove Hg(II) from water. The M-Ti₃C₂ 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-Ti₃C₂ 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 Hg₂Cl₂ on the edges of M-Ti₃C₂. Up to ∼95% of dimeric Hg₂Cl₂ can be efficiently recovered via facile thermal treatment. Notably, owing to the adsorbed ^•OH and energy released during the distinct interaction, M-Ti₃C₂ has been oxidized to TiO₂/C nanocomposites. And the TiO₂/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-Ti₃C₂ an outstanding candidate for rapid/urgent Hg(II) removal and recovery.