Highly Selective, Defect-Induced Photocatalytic CO Reduction to Acetaldehyde by the Nb-Doped TiO Nanotube Array under Simulated Solar Illumination.

The adsorption and activation of CO molecules on the surface of photocatalysts are critical steps to realize efficient solar energy-induced CO conversion to valuable chemicals. In this work, a defect engineering approach of a high-valence cation Nb-doping into TiO was developed, which effectively enhanced the adsorption and activation of CO molecules on the Nb-doped TiO surface. A highly ordered Nb-doped TiO nanotube array was prepared by anodization of the Ti-Nb alloy foil and subsequent annealing at 550 °C in air for 2 h for its crystallization. Our sample showed a superior photocatalytic CO reduction performance under simulated solar illumination. The main CO reduction product was a higher-energy compound of acetaldehyde, which could be easily transported and stored and used to produce various key chemicals as intermediates. The acetaldehyde production rate was over ∼500 μmol·g·h with good stability for repeated long-time uses, and it also demonstrated a superior product selectivity to acetaldehyde of over 99%. Our work reveals that the Nb-doped TiO nanotube array could be a promising candidate with high efficiency and good product selectivity for the photocatalytic CO reduction with solar energy.