Preparation And Visible-light-driven Photocatalytic Activites Of Mesoporous Hollow SiC-based Nanofibers

Nowdays,Energy shortages and chemical pollution are two major challenges with the rapid development of the world.Hydrogen energy is considered to be an ideal new energy source,with a series of advantages such as high combustion heat value,abundant resources,clean pollution-free,reduced fuel weight.Among the numerous proposed technologies.,semiconductor photocatalytic water splitting to produce hydrog enenergy source has been regarded as one of the most generally studied solar-fuel strategies for solving the current global energy crisis and environmental problem.Silicon carbide(SiC)is considered to be one of the important materials for third-generation semiconductors,with outstanding stability and photo-corrosion resistance.Although some progress has been made in current SiC photocatalysis research,it still faces the following major difficulties and challenges:i)low specific surface area;ii)poor surface adsorption;iii)low hydrogen production activity.Based on the above problems,this thesis has carried out some exploratory research work.Firstly,the preparation and tailored structure of mesoporous hollow SiC nanofibers photocatalyst materials have been realized by the exploration and optimization of the process,and then graphene grown in situ and CdS loaded are on its surface.The photocatalytic hydrogen production performance of SiC was enhanced by increasing the specific surface area and enhancing the separation and transport of photogenerated carriers.The research results obtained can be drawn as follows:(1)Polyvinylpyrrolidone(PVP)and polynitrosilane(PSN)were used as raw materials to prepare and tailored structure the mesoporous hollow SiC nanofibers by electrospinning and high temperature pyrolysis.The results show that the mass concentration of PVP and PSN in raw materials is one of the key parameters affecting the preparation of SiC mesoporous hollow nanofibers.The optimal photocatalytic H2 evolution rate of visible light is 7.67(pmol h-1 g-1,which is more than?2 times that of the pure SiC nanophotocatalyst reported.(2)G/SiC mesoprous hollow nanofibers were synthesized with graphene growth in situ on the surface of SiC via the epitaxial graphene method.The results suggest the graphene layers on SiC can be accurately controlled by the growth time.Due to the excellent electronic conductivity of graphene,its photocatahytic H2 evolution rate is 29.84 ?mol h-1 g-1 uder visible light irradiation,which is?3.9 times that of pristine SiC mesoporous hollow nanofibers,and the photocatalytic stability is effectively improved.(3)CdS/SiC hybrid photocatlysts were prepared with by hydrothermal treatment to introduce the CdS nanoparticles decorated on the preformed fiber matrix.The results suggest the photocatahytic H2 evolution rate is 124.65 ?mol h-1 g-1 uder visible light irradiation,which was profoundly enhanced for more than?16 times to that of pristine SiC counterparts,due to the formation of Z-type carrier transfer system between CdS and SiC to promote the effective separation of photogenerated carriers.(4)CdS/G/SiC ternary composite photocatlysts were fabricated by epitaxial graphene method and hydrothermal method,which combined the conductivity of graphene with the heterojunction advantage of CdS.The results suggest the photocatalyst exhibits excellent photocatalytic activity and stability under visible light.And the photocatahytic H2 evolution rat is up to 1544.91 ?mol h-1 g-1 uder visible light irradiation,which is?200 times that of pristine SiC mesoporous hollow nanofibers.