Impact of sodium ion impregnation on the photocatalytic hydrogen evolution activities of anatase/rutile mixed phase TiO2 nanomaterials

Abstract

The synthesis of sodium ion impregnated anatase/rutile mixed phase TiO₂ material was done by sol- gel method for understanding the solar hydrogen production activities. The prepared materials were characterized by X-ray powder diffraction analysis, Raman spectroscopic analysis, diffuse reflected absorption spectroscopy and Transmission electron microscopy analysis. The presence of sodium ion can influence the crystallanity, crystallite size and the photocatalytic efficiency of mixed phase TiO₂. The hydrogen evolution activities of the sodium impregnated TiO₂ and bare TiO₂ materials were compared by calculating the yield of H₂ gas evolved from the dissociation of H₂O. Even though the presence of rutile/ anatase mixed phase TiO₂ is suitable for hydrogen evolution under UV/visible light irradiation, it was found that under UV/visible light, bare TiO₂ can act as a good catalyst and gave a hydrogen evolution value of 134 µmol after 5 hrs of irradiation from 20 mg of the catalyst. However the sodium impregnated TiO₂ material showed lower hydrogen evolution as compared to bare TiO₂ and showed a value of 34 µmol under similar experimental condition. The variation in hydrogen evolution may be exhibited due to high crystallinity, large crystallite size and higher percentage of the rutile phase in bare TiO₂ compared sodium impregnated TiO₂ material. This study will be helpful for understanding the effect of alkali metal ion in metal oxide semiconductor and further understanding their detrimental effect on photocatalytic water splitting and related applications.