Ultra-fast and ultra-efficient removal of Cr (VI) by the aqueous solutions of monolayer MXene (TiCT).

Chromium (VI) removal is crucial to the safety of water resources, but there is still a lack of effective and fast dislodge methods, especially the on-site rapid remediation and emergency removal technology. Herein, the monolayer (ML) TiCT nanosheets (NSs) were prepared to remove Cr (VI) from water. The solution sample of the two-dimensional (2D) TiCT NSs demonstrate ultrafast adsorption kinetics (the concentration decreasing from 300 to 3 mg L in 10 min) and impressively high capacity (1483 mg g), which is several times higher than that of the most reported Cr (VI) adsorption by TiCT. The analysis of the adsorption kinetics and isotherm models indicates that the adsorption reaction is endothermic, with physical and chemical adsorption coexisting (mainly monolayer chemical adsorption). The joint study of the experimental analysis and theoretical calculation based on the density functional theory (DFT) demonstrates that the extraordinary removal performance of Cr (VI) is due to the synergetic effect of reduction reaction removal and electrostatic adsorption. It is found that the Cr (VI) is mainly reduced by the OH- terminals on TiC, and the detoxified Cr (III) is anchored on the surface of TiCT through complexation reaction with O terminal. The advantages of ultrafast adsorption kinetics and extra-high adsorption capacity of the single-layered TiCT for Cr (VI) removal make it a remarkable candidate for rapid and urgent removal of Cr (VI) wastewater.