Photocatalytic hydrogen evolution over SiO2-pillared and nitrogen-doped titanic acid under visible light irradiation Original Research Article

Silica-pillared and non-pillared H2Ti4O9 samples were doped with nitrogen from urea as a nitrogen precursor for visible light photocatalysis. The photocatalytic activities of the nitrogen-doped samples were evaluated for hydrogen evolution from aqueous methanol solution. Techniques such as XRD, FT-IR, TG-DSC, SEM, XPS, and UV–visible diffuse reflectance spectroscopy were adopted to explore the characteristics of the materials. The silica-pillared H2Ti4O9 sample is more stable than the non-pillared one, and its layered structure was retained well at temperatures up to 500 °C. The interlayer spacing of H2Ti4O9 was expanded from 2.7 Å to 7.2 Å after being pillared with silica. Silica pillaring could have a profound impact on nitrogen doping and the resultant photocatalytic activity. The interlayer spacing of the silica-pillared H2Ti4O9 did not change after nitrogen doping; in contrast, that of the non-pillared H2Ti4O9 was reduced by 44% after the same doping process, despite the fact that the non-pillared sample showed better nitrogen doping properties. With expanded interlayer spacing and better retained layered structure, the silica-pillared and nitrogen-doped H2Ti4O9 performed much better than the non-pillared counterpart for hydrogen evolution under visible light irradiation.