Highly Efficient and Selective Hg(Ⅱ) Removal from Water Using Multilayered Ti_3C_2O_x MXene via Adsorption Coupled with Catalytic Reduction Mechanism

摘要

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_3C_2 (Ti_3C_2O_x) (abbreviated as M-Ti_3C_2) nanosheets were prepared to remove Hg(Ⅱ) from water. The M-Ti_3C_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_3C_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_2Cl_2 on the edges of M-Ti_3C_2. Up to ～95% of dimeric Hg_2Cl_2 can be efficiently recovered via facile thermal treatment. Notably, owing to the adsorbed "OH and energy released during the distinct interaction, M-Ti_3C_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_3C_2 an outstanding candidate for rapid/ urgent Hg(Ⅱ) removal and recovery.