Defect-Mediated Crystallization of the Particulate TiO2 Photocatalyst Grown by Atomic Layer Deposition

Nanopowders or films of pure and mixed oxides in nanoparticulate form have gained specific interest due to their applicability in functionalizing high-surface-area substrates. Among various other applications, our presented work primarily focuses on the behavior of TiO₂ as a photocatalyst deposited by atomic layer deposition (ALD) on a quartz particle. The photocatalytic activity of TiO₂ on quartz particles grown by ALD was studied in terms of ALD growth temperature and post-treatment heating rate. Amorphous TiO₂ thin films (30 nm) were grown from tetrakis(dimethylamido)titanium (TDMAT) at 100 and 200 °C on quartz particles (0.35–3.5 μm) and crystallized using oxidative heat treatment at 500 °C with variable heating rates. The growth temperature was found to affect the TiO₂ defect structure: TiO₂ grown at 200 °C is black due to Ti³⁺ defects, whereas the film grown at 100 °C is white but contains some traces of the TDMAT ALD precursor. During the oxidative heat treatment, precursor traces desorbed and Ti³⁺ defects were oxidized. ALD TiO₂ grown at 100 °C crystallized as anatase, whereas the rutile-to-anatase ratio of 200 °C grown TiO₂ increased with the heating rate. The hydrogen production rate of mixed-phase TiO₂ was found to outperform that of anatase TiO₂.