Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions

This work investigated the suppression of photocatalytic activity of titanium dioxide (TiO₂) pigment powders by extremely thin aluminum oxide (Al₂O₃) films deposited via an atomic-layer-deposition-type process using trimethylaluminum (TMA) and H₂O as precursors. The deposition was performed on multiple grams of TiO₂ powder at room temperature and atmospheric pressure in a fluidized bed reactor, resulting in the growth of uniform and conformal Al₂O₃ films with thickness control at sub-nanometer level. The as-deposited Al₂O₃ films exhibited excellent photocatalytic suppression ability. Accordingly, an Al₂O₃ layer with a thickness of 1 nm could efficiently suppress the photocatalytic activities of rutile, anatase, and P25 TiO₂ nanoparticles without affecting their bulk optical properties. In addition, the influence of high-temperature annealing on the properties of the Al₂O₃ layers was investigated, revealing the possibility of achieving porous Al₂O₃ layers. Our approach demonstrated a fast, efficient, and simple route to coating Al₂O₃ films on TiO₂ pigment powders at the multigram scale, and showed great potential for large-scale production development.