Photocatalystic Water Splitting Efficiency Of Flame Made CuO_X/TiO₂ Catalyst

Photocatalytic water splitting has received more and more attention as a new way of solar energy utilization.However,for photocatalytic water splitting,it is facing two main problems:（1）Due to the limit of photocatalyst’s band structure,the light absorption capacity under visible light is really poor.（2）The poor efficiency of photogenerated electron-hole pairs separation which results in the recombination of a large number of electron-hole pairs instead of taking part in the redox reaction.First,the CuO/TiO₂ heterojunction photocatalyst was synthesized by flame spray pyrolysis method.The TEM analysis showed that the sample consisted of spherical particles with particle size of around 30 nm.The results show that the CuO enhances the photoreactivity of the sample under the visible light,and the light absorption capacity is enhanced with the increase of CuO content.During the photocatalytic water splitting experiment,the photocatalytic efficiency of CuO/TiO₂ heterojunction photocatalyst is much higher than that of pure TiO₂（P25）.Especially for the samples with 2%wt CuO,which showed the highest photocatalytic efficiency and the hydrogen production rate reached 88.8μmol/h at 12h,which was 17.5 times of the hydrogen production rate of P25.The results show that the existence of CuO/TiO₂ heterojunction can effectively facilitate the separation of electron-hole pairs,so that the electrons accumulate in the conduction band of TiO₂ and the holes move from the valence band of TiO₂ to the valence band of CuO.When the CuO content increased to 20%wt,the sample shows no photocatalytic water splitting capacity.It is found that the CuO content on the sample surface was much higher than that in the bulk phase and the CuO content on the surface was about 50%wt rather than 20%wt.Since the active sites on the TiO₂ surface where the redox reaction happens were covered by the excessive CuO on the surface,resulting in the deactivation of the photocatalyst.Then,after the analysis of the band structure of CuO/TiO₂ heterojunction,we find that there is a small upward peak between the conduction band of CuO and TiO₂,which will certainly affect the separation efficiency of electron-hole pairs.Therefore,CuO/TiO₂samples were proposed to be treated under H₂ atomsphere on chemisorption analyzer in order to preapare CuO,Cu₂O and TiO₂ mixed samples.The reduced samples showed better photocatalytic performance in the photocatalytic experiments than that untreated samples.It is shown that the heterojunction between Cu₂O and TiO₂ interface could be more efficient for the separation of electron-hole pairs and thus improving the photocatalytic efficiency.In summary,by using the CuO/TiO₂ heterojunction structure nano particles and the Cu_xO/TiO₂ heterojunction structure nano particles as the photocatalyst,the photocatalytic water splitting efficiency is successfully improved by increasing the light absorption capacity and facilitating the separation efficiency of photo electron-hole pairs.