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

Abstract

Sodium ion impregnated anatase/rutile mixed phase TiO₂ material has been synthesised by sol-gel method and characterised for understanding the solar hydrogen production activities. The presence of sodium ion can influence the crystallinity, crystallite size and photocatalytic efficiency of mixed phase TiO₂. The hydrogen evolution activities of the sodium impregnated TiO₂ and bare TiO₂ materials are 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 is found that bare TiO₂ can act as a good catalyst and gives a hydrogen evolution value of 134 μmol after 5 h of irradiation from 20 mg of the catalyst. However, the sodium impregnated TiO₂ material show lower hydrogen evolution as compared to bare TiO₂ and 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 to 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.