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@en

This work presents a novel chemical vapor deposition (CVD) approach that enables the deposition of ultrathin and conformal SiO₂ layers on TiO₂ anatase nanoparticles at room temperature using SiCl₄ and air containing water without the use of a catalyst. The morphology of the CVD-grown SiO₂ layers was found to be strongly dependent on the initial surface states of the TiO₂ nanopowders, which could be altered by applying a simple heat pretreatment. The deposition on untreated TiO₂ resulted in granular films, whereas on preheated TiO₂ highly uniform and conformal SiO₂ layers were obtained. By varying the SiCl₄ precursor dosing time and the number of CVD cycles, the thickness of the SiO₂ could be controlled at the nanometer level, which allowed us to investigate the influence of film thickness on the photocatalytic suppression ability. We found that a conformal SiO₂ layer with a thickness of 3 nm could sufficiently suppress the photocatalytic activity of anatase TiO₂ nanoparticles, which was demonstrated by the photodegradation of Rhodamine B. Our approach offers a simple, fast, feasible and low-temperature deposition method which can be directly applied to SiO₂ coating on nanoparticles in pigments and other fields, particularly heat-sensitive materials, and further developed for large-scale production.

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