MXene dots as photocatalysts for CO2 hydrogenation

Abstract

Four MXene dots (MDs) (Ti3C2, Ti2C, V2C and Nb2C) have been prepared by laser ablation of the corresponding MAX phases in aqueous medium and subsequent separation by double centrifugation. These MDs were characterized by atomic force and transmission electron microscopy that show, respectively, thickness between 3 and 7.5 nm corresponding to few-layer nanoparticles and homogeneous lateral dimensions between 2.5 and 5 nm with high crystallinity. IR spectroscopy indicates that Ti3C2 and Ti2C contain OH as surface terminal groups, while XPS indicates the presence of O on the surface for the four samples. MDs present the most intense absorption band in the UV region with onset below 400 nm. These samples exhibit photocatalytic activity for CO2 hydrogenation to CO and methane, following the order Ti3C2>Nb2C>Ti2C>V2C. Isotopic label experiments confirm CO2 as the origin of the photo products. Most of the photoresponse derives from the UV photons, the photocatalytic activity increasing with the temperature in the range from 200 to 300 °C. These results show the possibility of tuning the composition, surface terminal groups, and other structural parameters of MXenes to produce semiconducting materials exhibiting important photocatalytic activity. Considering their versatility, flexible composition, and tunability, MXenes appear as promising 2D materials with intrinsic photoresponse to develop highly efficient photocatalysts.