Photocatalytic CO Reduction Using TiCX (X = Oxo, OH, F, or Cl) MXene-ZrO: Structure, Electron Transmission, and the Stability.

CO photoreduction using a semiconductor-based photocatalyst is a promising option for completing a new carbon-neutral cycle. The short lifetime of charges generated owing to light energy is one of the most critical problems in further improving the performance of semiconductor-based photocatalysts. This study shows the structure, electron transmission, and stability of TiCX (X = oxo, OH, F, or Cl) MXene combined with a ZrO photocatalyst. Using H as a reductant, the photocatalytic CO formation rate increased by 6.6 times to 4.6 μmol h g using MXene (3.0 wt %)-ZrO compared to that using ZrO, and the catalytic route was confirmed using CO to form CO. In clear contrast, using HO (gas) as a reductant, CH was formed as the major product using TiCX MXene (5.0 wt %)-ZrO at the rate of 3.9 μmol h g. Using CO and HO, CH, CH, and CH were formed besides HCO, demonstrating that the C source was the partial decomposition and hydrogenation of TiCX. Using the atomic force and high-resolution electron microscopies, 1.6 nm thick TiCX MXene sheets were observed, suggesting ∼3 stacked layers that are consistent with the Ti-C and Ti···Ti interatomic distances of 0.218 and 0.301 nm, respectively, forming a [TiC] octahedral coordination, and the major component as the X ligand was suggested to be F and OH/oxo, with the temperature increasing by 116 K or higher owing to the absorbed light energy, all based on the extended X-ray absorption fine structure analysis.