Monoclinic Tungsten Oxide with {100} Facet Orientation and Tuned Electronic Band Structure for Enhanced Photocatalytic Oxidations

Exploring surface-exposed highly active crystal facets for photocatalytic oxidations is promising in utilizing monoclinic WO₃ semiconductor. However, the previously reported highly active facets for monoclinic WO₃ were mainly toward enhancing photocatalytic reductions. Here we report that the WO₃ with {100} facet orientation and tuned surface electronic band structure can effectively enhance photocatalytic oxidation properties. The {100} faceted WO₃ single crystals are synthesized via a facile hydrothermal method. The UV-visible diffuse reflectance, X-ray photoelectron spectroscopy valence band spectra, and photoelectrochemical measurements suggest that the {100} faceted WO₃ has a much higher energy level of valence band maximum compared with the normal WO₃ crystals without preferred orientation of the crystal face. The density functional theory calculations reveal that the shift of O 2p and W 5d states in {100} face induce a unique band structure. In comparison with the normal WO₃, the {100} faceted WO₃ exhibits an O₂ evolution rate about 5.1 times in water splitting, and also shows an acetone evolution rate of 4.2 times as well as CO₂ evolution rate of 3.8 times in gaseous degradation of 2-propanol. This study demonstrates an efficient crystal face engineering route to tune the surface electronic band structure for enhanced photocatalytic oxidations.