Study On Preparation And Properties Of Noble Metal/semiconductor Core Shell Structure

With the development of society and the increasingly exhaustion of fossil fuels,the energy crisis have been become a key problem to restrict the sustainable development of human.Photocatalytic water splitting to produce H₂ by solar energy based on semiconductor nanomaterials is one of the most promising way to remit the energy crisis.In this thesis,we prepared a series of gold nanorod?AuNR?coated by metallic sulfide core-shell photocatalysts and investigated their structure,optical and photocatalytic properties.The thickness of Ag coated on surface of AuNR have been adjusted successfully by change the amount of Ag precursor,as a result the optical propertries are changed.With the increase of Ag's thickness,the longitudinal plasmon peak of AuNR is blue-shift and the ratio of transverse and longitudinal plasmon peaks also increases.In addition,the plasmon peak of Ag also appeare.The Au NR@Ag with different thickness is sulfurized in aqueous solution,and then the AuNR@CdS,AuNR@PbS and AuNR@Cu_?2-X?S with different thickness are achieved by cation exchange.The results show that the hydrogen production rate increased first and then decreased with the thickness increase of the metallic sulfide shell.The AuNR@CdS,AuNR@PbS and AuNR@Cu_?2-X?S with a thickness of 15 nm have the highest activity for hydrogen evolution and the correspongding rates are 2.22 mmol h^-1 g^-1,1.98 mmol h^-1 g^-1 and1.36 mmol h^-1 g^-1,respectively,which probably results from suitable energy band structure,light absorption and electron diffusion length.AuNR@CdS exhibits the highest rate for hydrogen evolution among the three samples due to more proper energy band position of CdS than AuNR@PbS.The poor crystalline of Cu_?2-X?S for AuNR@Cu_?2-X?S sample lead to many defects that could serve as charge recombination centers.AuNR@CdS/PbS core@shell structure with heterogeneous shell is prepared in aqueous solution.With the increase of thickness,the absorption spectrum of photocatalysts red-shift can be observed.AuNR@CdS/PbS coated shell with the thickness of 4 nm,9 nm,15 nm and 21 nm are obtianed by control the thickness of Ag and the rates for hydrogen evolution are 1.42 mmol h^-1 g^-1,1.87 mmol h^-1 g^-1,3.14mmol h^-1 g^-1 and 2.07 mmol h^-1 g^-1,respectively.The sample with a thickness of 15nm has the highest rate for hydrogen evolution,which probably results from suitable energy band structure,light absorption and electron diffusion length.Compared with pure shell,the heterogeneous shell have higher activity due to the heterojunction facilitating photo-induced carriers transfer process similarly Z-scheme photocatalyst.