Engineering Anatase/Brookite TiO2Heterophase Junctions via Nitrogen Doping to Improve Photocatalytic Transfer Hydrogenation

Engineering a heterophase junction is an efficient approach to improve the photocatalytic performance of semiconductors. Herein, a series of nitrogen-doped TiO2with anatase/brookite heterophase junctions (denoted as N(x)-A/B(y)) have been prepared by adding urea into a titanium tetraisopropoxide hydrothermal reaction solution and followed by annealing in air. It was found that TiO2with a pure anatase phase could be obtained from the titanium tetraisopropoxide reaction solution, and the addition of urea led to the formation of nitrogen-doped TiO2-containing anatase/brookite heterophase junctions. Characterization results suggested that the doped nitrogen shrunk the band gap of TiO2to improve light harvesting, while the anatase/brookite heterophase junction with well-matched band alignment effectively improved the charge separation. As a result, the obtained N(x)-A/B(y)catalysts exhibited excellent catalytic performance in the photocatalytic transfer hydrogenation (PCTH) of aromatic aldehydes with methanol as a hydrogen source. In particular, N(0.21)-A/B(16.1)allowed for almost quantitative hydrogenation of aromatic aldehydes to alcohols (yield of 82–98%), while pure anatase and brookite TiO2were far less efficient (less than 30%). Moreover, the N(x)-A/B(y)catalysts were highly stable and could be efficiently reused several times. This work presents the first example of engineering an anatase/brookite TiO2heterophase junction via nitrogen doping for efficient PCTH. The excellent catalytic performance, together with a safe operation process, makes such transfer hydrogenation highly promising for industrial applications.