Preparation Of CVD Graphene-TiO₂-based Composite Photocatalyst And Study On Its Photocatalytic Performance Towards Water Splitting

Nowdays,the energy crisis and environmental pollution have become key problems which cannot be ignored.How to obtain abundant and clean energy is imminent.Hydrogen energy is a promising energy sources which is clean,efficient and renewable.Among the technologies of hydrogen production,photocatalytic water splitting for hydrogen evolution,which can use semiconductor catalysts to convert solar energy into hydrogen energy,is considered to be the most ideal approach.Therefore,how to develop efficient and stable photocatalysts has become a scientific problem that needs to be solved urgently.Aims at the current problems of semiconductors using in the photocatalytic water splitting,TiO₂has been chosen as the research object,which was modified by CVD graphene,hemicellulose,and co-catalyst Pt to prepare CVD graphene-TiO₂-Hemicellulose-Pt composite photocatalyst.Then a variety of experimental methods were used to characterize the as-prepared material,and the mechanism of hydrogen production was be discussed.The main research contents are as follows:1.The high-quality graphene were prepared by adjusting the parameters of the CVD method and used to modify TiO₂to obtain the CVDG-TiO₂photocatalyst.The as-prepared materials were used for photocatalytic water splitting.Compared with pure TiO₂and reduced graphene oxide-TiO₂（RGO-TiO₂）,the CVDG-TiO₂samples prepared under the optimal conditions showed the best activity,over which the amounts of hydrogen production reached at 226.8μmol in 3 h under UV light and the hydrogen production rate reaches at 68.2μmol·h^-1.Through the analysis of the morphological structure,light absorption,photoelectrochemistry and charge transfer of the catalyst,the direct correlation between the conductivity of graphene and the photocatalytic activity was clarified.It was revealed that graphene is significant for the construction of high-efficiency TiO₂-based photocatalysts.2.The hemicellulose was used to modify the CVD graphene-TiO₂-based composite by the sol-gel method.When the addition amount of hemicellulose was 2g/100 m L of titanium sol,the material showed better photocatalytic activity for hydrogen production under visible light,of which the amounts of hydrogen production reached at 40.9μmol in 3 h under visible light and the hydrogen production rate reached at 13.6μmol·h^-1.The high photocatalytic performance of the catalyst can be attributed to the following reasons:Firstly,the doping of hemicellulose reduces the agglomeration of TiO₂particles,which conduces to increase the reactive sites,reduce the recombination of photo-generated carriers,and improve the photocatalytic activity.Secondly,C from hemicellulose plays a certain sensitization role;and the N of hemicellulose enters the oxygen lattice of TiO₂to form Ti-N-O bonds.The synergistic effect of C sensitization and N doping narrowed the band gap of TiO₂,broadened the light response range,promoted the separation of photogenerated carriers,and increased the rate of hydrogen production.3.To enhance the photocatalytic activity,the co-catalyst Pt is deposited on the CVDG-T-2H composite by chemical reduction method.Compared with CVDG-TiO₂-2H,when the loading ratio of Pt is 0.5%,the 0.5%Pt-CVDG-T-2H sample shows better photocatalytic activity for hydrogen production under visit light,of which the amounts of hydrogen production reacted at 245.5μmol in 3 h under visit light and the hydrogen production rate reached at 81.7μmol·h^-1.