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 degrees C on quartz particles (0.35-3.5 mu m) and crystallized using oxidative heat treatment at 500 degrees C with variable heating rates. The growth temperature was found to affect the TiO2 defect structure: TiO2 grown at 200 degrees C is black due to Ti3+ defects, whereas the film grown at 100 degrees 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 degrees C crystallized as anatase, whereas the rutile-to-anatase ratio of 200 degrees C grown TiO2 increased with the heating rate. The hydrogen production rate of mixed-phase TiO2 was found to outperform that of anatase TiO2.