Synthesis of Mesoporous TiO₂/Boron-Doped Diamond Photocatalyst and Its Photocatalytic Activity under Deep UV Light (λ = 222 nm) Irradiation

There is a need for highly efficient photocatalysts, particularly for water purification. In this study, we fabricated a mesoporous TiO₂ thin film on a boron-doped diamond (BDD) layer by a surfactant-assisted sol-gel method, in which self-assembled amphiphilic surfactant micelles were used as an organic template. Scanning electron microscopy revealed uniform mesopores, approximately 20 nm in diameter, that were hexagonally packed in the TiO₂ thin film. Wide-angle X-ray diffraction and Raman spectroscopy clarified that the framework crystallized in the anatase phase. Current⁻voltage (I⁻V) measurements showed rectification features at the TiO₂/BDD heterojunction, confirming that a p⁻n hetero-interface formed. The as-synthesized mesoporous TiO₂/BDD worked well as a photocatalyst, even with a small volume of TiO₂ (15 mm × 15 mm × c.a. 1.5 µm in thickness). The use of deep UV light (λ = 222 nm) as a light source was necessary to enhance photocatalytic activity, due to photo-excitation occurring in both BDD and TiO₂.