Photocatalytic CO2 Reduction Using Ti3C2X y (X = Oxo, OH, F, or Cl) MXene-ZrO2: Structure, Electron Transmission, and the Stability

CO2 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 Ti3C2Xy (X = oxo, OH, F, or Cl) MXene combined with a ZrO2 photocatalyst. Using H-2 as a reductant, the photocatalytic CO formation rate increased by 6.6 times to 4.6 mu mol h(-1) g(cat)(-1) using MXene (3.0 wt %)-ZrO2 compared to that using ZrO2, and the catalytic route was confirmed using (CO2)-C-13 to form (CO)-C-13. In clear contrast, using H2O (gas) as a reductant, CH4 was formed as the major product using Ti3C2Xy MXene (5.0 wt %)-ZrO2 at the rate of 3.9 mu mol h(-1) g(cat)(-1). Using (CO2)-C-13 and H2O, (CH4)-C-12, (C2H6)-C-12, and (C3H8)-C-12 were formed besides (H2CO)-C-12, demonstrating that the C source was the partial decomposition and hydrogenation of Ti3C2Xy. Using the atomic force and high-resolution electron microscopies, 1.6 nm thick Ti3C2Xy MXene sheets were observed, suggesting similar to 3 stacked layers that are consistent with the Ti-C and Ti<middle dot><middle dot><middle dot>Ti interatomic distances of 0.218 and 0.301 nm, respectively, forming a [Ti6C] 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. [GRAPHICS] .