Cd_xZn_1-xS Nanoparticles Synthesis And Study For Photocatalyst Properties Under Visible Light

Due to the dwindling of non-renewable fossil energy reserve and increasingly environmental pollution by burning of fossil fuels,energy issue has become a huge challenge toward humanity.Seeking renewable,sustainable and environment-friendly new energy has become an important work of researchers and technical engineers.Hydrogen has high burning value and the combustion product is water,so the hydrogen is great potential as a clean and renewable energy.In this regard,the use of solar energy to produce hydrogen from photocatalytic water splitting is a promising way to solve global energy crisis.In many photocatalytic semiconductor materials,CdS and ZnS are two important photocatalysts.The band gap of CdS is 2.4eV,being capable of absorbing visible light with ?<510nm,but it is not stable under illumination.ZnS has band gap of 3.6eV,which only responds to ultraviolet light.By transition metal doping,ZnS could product hydrogen under visible light irradiation.However the photocatalytic activity is not high.Recent studies have found that a solid solution formed between ZnxCd1-xS has better band structure and superior catalytic activity.It is an ideal visible light catalytic material.After forming a solid solution the position of conduction band of ZnxCd1-xS is more negative than that of CdS,which means that the corresponding hydrogen production will be higher than CdS catalyst.Such advantage has been confirmed by recent experiments reported.In this thesis,a variety of chemical methods were used to prepare CdxZn1-xS nanocrystals with adjustable component.The morphology,composition,crystal structure,absorption edge,surface area,and photocatalytic activities of the samples were characterized.According to the experimental results,The mechanisms for the CdxZn1-xS photocatalysts toward hydrogen production were discussed.Particularly conclusion as below:(1)CdxZn1-xS nanocrystals with tunable component were fabricated through co-precipitation method.The results showed that the products were cubic phase with solid solution structures.When the atomic ratio of the cadmium and zinc is 1:1,we got the highest efficiency of photocatalytic hydrogen production under visible light,which was about 774mol/h·g.(2)The morphology,the structure and the photocatalytic activity of CdxZn1-xS nanocrystals were studied by changing the mole ratio of cadmium and zinc source while fixing the total moles of reactants.Through X-ray diffraction data we found that the CdxZn1-xS nanocrystals were not a simple physical mixing of zinc sulfide and cadmium sulfide,but a solid solution with cubic structure.Through scanning electron microscope analysis,it can be seen that the CdxZn1-xS nanocrystals is uniform with size ranging from 4nm to 8nm.The results of specific surface area analyzer test showed that Cd0.2Zn0.8S had the largest specific surface area of about 207.5899 m2/g.Photocatalytic hydrogen rate results showed the Cd0.5Zn0.5S possessed the best efficiency of photocatalytic hydrogen production of up to 1516.67 ?mol/h.g.(3)The morphology,the structure and the photocatalytic hydrogen production rate of the CdxZn1-xS nanocrystals were investigated by fixing the ratio of cadmium:zinc precursor with 1:1 while using Tu or TAA(CH3CSNH2)as the S source.The results showed that all of the prepared Cd0.5Zn0.5S nanocrystals had cubic structure.Spherical volvox structured Cd0.5Zn0.5S with diameter 300-500nm were formed when using TU as the S source.The specific surface area was measured to be 49.8569m/g and significant blue shift was observed by comparing the absorption edge of Cd0.5Zn0.5S prepared by sodium sulfide.While TAA as the S source,the Cd0.5Zn0.5S nanocrystals(20nm)aggregated with specific surface area of 123.2770m2/g.Obvious red shift was observed by comparing the absorption edge of Cd0,5Zn0.5S prepared by sodium sulfide.Through examination of the photocatalytic H2 production of the Cd0.5Zn0.5S samples,it's showed that the activity of Cd0.5Zn0.5S by TAA was only half of samples by Na2S,while the Cd0.5Zn0.5S by use of TU had almost no hydrogen generation.(4)We synthesized Cdo.5Mno.5S nanoparticles using solvent-thermal method with different sulfur sources.According to the XRD analysis,all the synthesized Cd0.5Mn0.5S products were mixture with ?-MnS phase and we suspect that small amount of Mn can be doped into CdS lattice.There were so much a-MnS with the synthesized Cd0.5Mn0.5S nanoparticles when using Na2S or TAA as S sources,that the adsorb edge was not clear.Combined the BET tests and photo-catalyst performance results,we found that the Cd0.5Mn0.5S synthesized with organic sulfur source TAA had larger specific surface area,but it was less active than the Cd0.5Mn0.5S synthesized with inorganic sulfur source Na2S,which demonstrated that organic sulfur source might decrease the surface active sites of the samples.