Efficient Photocatalytic CO Reduction with High Selectivity for Ethanol by Synergistically Coupled MXene-Ceria and the Charge Carrier Dynamics.

The primary factors that govern the selectivity and efficacy of CO photoreduction are the degree of activation of CO on the active surface sites of photocatalysts and charge separation/transfer kinetics. In this context, the rational synthesis of heterostructured MXene-coupled CeO-based photocatalysts with different loading concentrations of TiCMXene via a one-step hydrothermal approach has been undertaken. These photocatalysts exhibit a shift in X-ray diffraction peaks to higher 2θ values and changes in stretching vibrations of 5 wt % TiCMXene/CeO(5-TC/Ce) that indicate interaction between TiCMXene and CeO. Moreover, XPS analysis confirms the presence of the Ce/Ce states. A sharp band at 2335 cm observed during the CO photoreduction process corresponds to bidentate b-CO, which facilitates the adsorption of CO at the surface of the catalyst as revealed by the TPD analysis. Furthermore, the Schryvers test and NMR analysis were undertaken to confirm the formaldehyde intermediate formation during CO photoreduction to CHOH. The decrease in emission intensity, reduced lifetimes (2.68 ns), and lower interfacial resistance, as revealed by PL, TR-PL, and EIS analysis, imply an efficient charge separation and charge transfer in the case of the TiCMXene/CeO heterojunction. The decrease in the intensity of peaks in the EPR spectrum in the case of 5-TC/Ce further confirms efficient charge transfer kinetics across the interface. The optimized 5-TC/Ce shows CO reduction with a drastically enhanced yield of ethanol on the order of 6127 μmol g at 5 h with 98% selectivity and 7.54% apparent quantum efficiency, which is 6-fold higher than that of ethanol produced by bare CeO. Herein, CeO that acts as a redox couple (Ce/Ce) when coupled with MXene having a metallic nature that reduces the electron transfer resistance is in unison, enabling an enhanced mobilization of electrons. Thereby, the synergistic coupling of TiCMXene with CeO leads to an efficient photoreduction of CO under visible light illumination.