Single-atom Mo decorated TiO2 hollow sphere catalyst: Engineering local electric field polarization to boost photocatalytic conversion of diluted CO2.

The photocatalytic reduction of carbon dioxide (CO2) using semiconductor materials is considered a promising approach to address the challenge of diluted CO2. However, challenges such as weak reactant adsorption, sluggish mass transfer kinetics, and high recombination rate of photogenerated charge carriers limit catalytic efficiency. To address the critical challenges, this study designed and synthesized a hollow TiO2 nanosphere photocatalyst anchored with atomically dispersed molybdenum (Mo) sites. The catalyst achieves efficient conversion of diluted CO2 through a multiscale engineering strategy. At the micro-nano scale, the confinement effect of the hollow structure significantly enhances light absorption and creates a localized high-concentration CO2 microenvironment, thereby improving mass transfer kinetics at the gas-solid interface. At the atomic scale, the lattice-doped Mo single atoms provide new catalytic active centers by forming stable Mo-O-Ti coordination structures. It is noteworthy that as a representative catalyst, the Mo/TiO2-4 exhibits outstanding performance under 15% CO2 concentration, achieving a carbon monoxide (CO) production rate of 16.0 μmol·g-1·h-1 with a high selectivity of 74.9%. Density functional theory (DFT) calculations and experimental results suggest that the improved photocatalytic performance is associated with the combined effects of the hollow TiO2 framework and atomically dispersed Mo-O-Ti sites. The hollow structure facilitates light utilization and reactant transport, while the Mo single-atom sites modulate the local electronic structure and promote charge separation and CO2 activation. This mechanism effectively overcomes the charge transport bottleneck of TiO2 from an electron coupling perspective, promoting charge separation and reactant activation. This study reveals the enhancement mechanism of microscopic morphology regulation and single-atom electronic structure engineering, providing new theoretical insights and design strategies for developing efficient photocatalytic materials.