Suppressing Charge Recombination by Engineering Homojunctions in Brookite TiO₂ Nanorods for Enhanced Photocatalytic Hydrogen Evolution

Semiconductor junctions can enhance separation of photopromoted charge carriers and broaden the light harvesting range and hence are an effective approach to improve the performance of photocatalysts. Typical semiconductor junctions used in photocatalysis (heterojunctions) are formed by bringing two different semiconductors into contact, while homojunctions constructed by interfacing domains of the same semiconductor phase are less explored. Herein, we introduce a method to engineer homojunctions at the surface of brookite TiO₂ nanorods. We first decorated the nanorods with Cu nanoparticles (masking) and then treated the Cu-decorated nanorods by ultrasonication. This treatment introduces defects in the exposed surface of TiO₂, while Cu-coated areas remain unaltered. Once the Cu decorations are selectively etched off (demasking), “patches” of pristine oxide surrounded by reduced areas are created, forming surface homojunctions. The formation of surface defects and homojunctions is confirmed by Raman, X-ray photoelectron, and photoluminescence spectroscopies. We show that homojunction engineering is the dominant reason for the increase of photocatalytic H₂ evolution by 30 times compared to the pristine material. In contrast, the homogeneous reduction of the TiO₂ nanorods improves the photocatalytic activity of brookite nanorods only by a factor of 3.