Visible-Light-Responsive Layered Titanium Oxide/Tin Indium Oxide Catalysts for Hydrogen Production

Visible-light-responsive layered titanium dioxide/tin indium oxide (TiO₂/ITO) catalysts prepared on unheated glass slides by DC magnetron sputtering were investigated in this study. Transmittance spectra of the catalyst revealed that an interference pattern gradually appeared at wavelengths of 550–650 nm which indicated a strong light absorption up to this region. The red-shift may be ascribed to the difference in both compositions and phase structures of the layered catalyst. X-ray diffraction (XRD) and scanning electron microscopy (SEM) exhibited a strong columnar growth morphology with highly faceted grains and a distinct (211) texture. Selected area electron diffraction (SAED) measurements also confirmed the crystalline nature of the layered catalyst. The SIMS elemental depth profiles showed that tin atoms permeated into the overlaid TiO₂ film. This could be resulted from the diffusion of tin from the intercalated ITO thin film during the TiO₂ deposition. It suggested that the tin atoms played an important role on the microstructure formation and on the catalytic property of the layered catalyst. This was also confirmed by the cross-sectional TEM images where a layer of crystalline anatase TiO₂ grown epitaxially above the intercalated ITO thin film was observed. In addition, a better crystalline TiO₂ film with larger grains of 120–180 nm and a higher specific surface area of 1.55 was obtained on successively coated ITO substrate. The layered catalysts showed significant photocatalytic activity on methylene blue (MB) degradation illuminated by ultra-violet (UV 365 nm) and visible light (420 < λ < 620 nm) sources. A preliminary study on water splitting for hydrogen production showed that a noticeable amount of hydrogen was generated at Pt cathode by employing electrical potential (∼0.5 V) and UV-light and visible (λ > 420 nm) sources via a TiO₂/ITO anode.