Pt/TiO 2 nanotube photocatalyst - Effect of synthesis methods on valance state of Pt and its influence on hydrogen production and dye degradation.

Direct conversion of solar energy into clean fuels is emerging as an efficient way for the future energy generation and solving environmental issues. Especially, photocatalytic splitting of water into H2 under solar light irradiation is one of the best techniques for clean energy production. Also, decomposition of organic pollutants using solar light is an urgent need to protect the environment. Hence, in the present study, we studied Pt-TiO2 nanotubes based composites for H2 generation and methyl orange dye degradation under solar light irradiation and compared the effect of deposition methods namely photo-deposition and chemical reduction methods. We have achieved the highest rate of H2 generation activity compared to other Pt-TiO2 based composite photocatalysts reported previously, and it is ≈173 mmol·h-1 ·g-1 cat for both photo-deposited and chemically reduced Pt/TiO2 nanotubes. This is about 46.8 folds higher than the pristine TiO2 nanotubes at the same experimental conditions. The selected catalysts were tested for degradation of methyl orange dye, where the catalyst prepared by chemical reduction method showed improved activity (94% degradation in 30 min) compared to the one which is prepared by photo-deposition method (50.5% degradation in 30 min). XPS analysis revealed that the photo-deposited catalyst consist only metallic Pt⁰, while the chemical-reduction yielded Pt with multiple oxidation states, Pt⁰, Pt2+ and Pt4+ .