Synthesis And Application Properties Of Ⅱ-Ⅵ Semiconductor/SnO₂Nano Structure Composite Films

Metal oxides find widespread scientific interest and practical utility due to theirwide-ranging optical and electronic properties. Recently, acute interest in metal oxideshas been driven by interest in applications such as photovoltaic energy conversion andphotocatalytic activity. Among these materials, Tin dioxide （SnO₂） is regarded as asuitable material for extensively investigating in the photovoltaic field owing to itschemical stability, non-toxicity, low cost, excellent optical and electrical properties.The optical band gap of SnO₂is about3.6eV. SnO₂possesses certain inherentadvantages such as higher electron mobility (100-200cm²V^-1S^-1) and more positiveconduction band edge position than TiO₂. The high electron mobility leads to fastertransport of photoinjected electrons to a transparent conductive oxide current collector,while the more positive conduction band edge position facilitates electron injectionfrom low band semiconductors. Since the morphological, structure, anddimensionality of semiconductors are vital parameters for their properties, developinga simple and facile solution routes to prepare nanomaterials is very important for theirapplication. Compared to nanoparticles,1D nanorods have efficient charge separationand transport properties. And the films with mesoporous1D single crystallinenanostructures aggregates of submicrometer size, which have the structural preference of large surface areas and excellent light scattering. In this thesis, we will focus on thepreparation of the SnO₂films. The synthesis and photoelectrochemical/photocatalyticproperties of SnO₂/Ⅱ-Ⅵ semiconductor composite filmare investigated. The maincontents are as follows:（1） High transparent SnO₂nanorod array has been prepared on FTO substrate viaa facile thermal evaporation mixture of SnCl₂·2H₂O and ZnCl₂in air atmosphere. Theinfluences of the amount of zinc chloride and heating rate on the morphology andstructure of SnO₂films have been studied in the experiment. Studies have shown thatZnCl₂played an important role in obtaining high transparent SnO₂nanorod array. Apossible growth process of high transparent SnO₂nanorod array was proposed in thethesis.（2） CdS thin film was deposited on the SnO₂nanorod array by CBD method, thecorresponding PEC property of the film had been studied in this part. Forthree-electrode measurements do not give the parameters of the cell but rather theparameters of photoelectrode. The data measured from three-electrode measurementshave been corrected. After CdCl₂treatment, the CdS/SnO₂composite film showsbetter photovoltaic property. A maximum1.19mA cm-2short circuit current densityand0.29%conversion efficiency under one sun illumination has been achieved.（3） For the first time, the SnO₂spherical particles film was grown directly onFTO substrates by using one step hydrothermal method. The spherical structuresactually are composed of number of nanorods, with diameter from500nm to2μm. Inthis work, CdS QDs-sensitized and CdS/CdSe QDs co-sensitized SnO₂sphericalparticles film on FTO were prepared by using the successive ionic-layer adsorptionand reaction （SILAR） method, their optical and photoelectrochemical properties wereinvestigated. With increasing the number of SILAR cycles, the optical absorption andphotoelectrochemical properties of CdS QDs-sensitized SnO₂spherical particles filmwere improved. The Jscand η increased obviously with increasing layers of CdS QDsand approached a maximum value of1.47mA cm-2and0.22%at5cycles of CdSQDs. After CdSe QDs are deposited on CdS（5c）/SnO₂photoelectrodes, the lightabsorbance of the CdS/CdSe QDs co-sensitized SnO₂spherical particles film in visible region is further enhanced. The Jscand η increased a maximum value of2.41mA cm-2and0.34%at4cycles of CdSe QDs deposited on CdS（5c）/SnO₂photoelectrode.（4） The SnO₂elongated octahedral nanoparticles film was firstly grown directlyon FTO substrates by using one step hydrothermal method, and CdS QDs weredeposited on the surface of the SnO₂nanocrystals by using the successive ionic-layeradsorption and reaction （SILAR） method to act a light absorber. Theirphotoelectrochemical and photocatalytic properties were investigated in this part.With increasing the number of SILAR cycles, the photoelectrochemical andphotocatalytic properties of CdS QDs-sensitized SnO₂elongated octahedralnanoparticles film were improved. The Jscincreased a maximum value of0.6mA cm-2at6cycles of CdS QDs deposited on SnO₂elongated octahedral nanoparticles film.After visible-light irradiation for140min, almost all MO have been degraded byCdS（6）/SnO₂film. And the film of CdS（6）/SnO₂shows good photocatalytic stability.The corresponding mechanism for the CdS/SnO₂photocatalytic degradation of theMO in our experiment was proposed in the paper...