Design&Synthesis Of Carbon/Transition Metal Composites And The Application In Photocatalytic Water Splitting

Harvesting solar energy for the production of hydrogen from water is an ultimate clean and renewable energy strategy for the global environmental and the energy crisis.The design and fabrication of high-efficiency,stable and low-cost photocatalysts are key issues for the water splitting.Carbon-based materials have been widely used in many fields(such as chemical sensing,photocatalysis,drug and gene delivery)because of low cost,excellent physical and chemical properties.In this paper,three kinds of carbon/transition metal composites were pepared by pyrolysis method or hydrothermal method.The photocatalytic activity of water splitting for as-pepared samples was investigated under solar light without any sacrificial agents.This paper introduced the preparation,characterization methods,photocatalytic properties of muti-doped carbon based catalysts,CDs/BiVO4QDs,BiVO4/CDs/CdS compistes,and further explored the reaction mechanism of photocatalytic water splitting of the catalysts.1.A modified method of solid-state synthesis of phthalocyanine(Pc)was used to prepare "multi-element doped carbon nanostructure"[(SMPc)n/CDs,M = Cr,Cd,Fe,Zn,Sm,Ce,Eu,Pr,Er],which CDs as a reaction agent was introduced.Under solar light illumination,these photocatalysts exhibited efficient photocatalytic ability and photostability for overall water splitting without sacrificial agents.The rate of H2 production used(SCrPc)n/CDs or(SSmPc)n/CDs as a photocatalyst was 0.46,1.04?mol/h,respectively.The photocatalytic reaction mechanism was studied by electrochemical measurements,UV-Vis and so on,the results indicated the(SMPc)n/CDs(M = Cr,Cd,Fe,Zn)splits water into H2 and O2 through a two-electron pathway,(SMPc)n/CDs(M = Re = Sm,Ce,Eu,Pr,Er)photocatalysts is via a four-electron pathway.In this catalyst system,the CDs in(SMPc)n/CDs nanostructure play important roles for photocatalytic water splitting,which not only improve charge seperation but more importantly provide active reduction reaction sites.2.The CDs/BiVO4QDs composites were prepared by a simple reflux method and the BiVO4 QDs were synthesized through a hydrothermal method.The structure,properties and reaction mechanism of catalysts were characterized by XRD,Raman,N2 adsorption-desorption isotherm,TEM,HRTEM,XPS,UV-Vis,electrochemical measurements.The experimental results showed that the H2 evolution of 0.92 ?mol/h with 5%CDs/BiVO4QDs(mass ratio of CDs/BiVO4 QDs = 0.05/1)as photocatalyst is about 4 times to that of BiVO4 QDs(0.21 ?mol/h)and the enhanced the photocatalytic performance of CDs/BiVO4QDs in H2 evolution may mainly attribute to the extended photo-responding range and highly efficient charge carrier separation.Overall water splitting over CDs/BiVO4QDs is realized via a two-electron pathway and CDs and BiVO4 QDs should be reduction and oxidation reaction active sites,respectively.3.BiVO4/CDs composites were prepared by hydrothermal method and BiVO4/CDs/CdS were obtained by a facile precipitation method.In this BiVO4/CDs/CdS Z-scheme system,BiVO4 and CdS nanoparticles can serve as O2 evolution photocatalyst and H2 evolution photocatalyst,repectively,and CDs can be used as solid electron mediator for photocatalytic water splitting under visible-light illumination in the absence of sacrificial reagents.The structure and properties of catalysts were characterized by XRD,TEM,UV-Vis,XPS and so on.The photocatalytic water splitting experimentally demonstrated that BiVO4/CDs/CdS exhibited excellent photocatalytic performance and stability,owing to reduce the recombination of photoexcited charge carriers and extended lifetime of the corresponding carriers.The rate of H2 and O2 evolution were 1.24 and 0.62 ?mol/h,respectively.The complete photocatalytic water splitting was achieved.