Synthesis And Characterization Of Bismuth-based Metal-semiconductor Heterostructure Nanomaterials

Metal-semiconductor heterostructure nanomaterials have attracted much attention due to their novel structures.Because of the existence of heterojunction can effectively control the electron,hole transmission,so that it has a unique photoelectric properties,interface characteristics,thermoelectric properties,catalytic properties and fluorescence characteristics.It is well known that the composition,structure,size and morphology of nanomaterials greatly affect its intrinsic properties.However,at present the synthesis of metal-semiconductor heterostructure nanomaterials has the disadvantages of uneven size,defective interface,complicated synthesis and large environmental hazards,which will constrain its performance research and widely used.Thus a great deal of effort is made to study the properties of metal-semiconductor heterostructure nanomaterials by controlling their size and morphology.In the past years,electrodeposition,CVD,microwave-assisted,template method and epitaxial growth have all been devoted to the synthesis of metalsemiconductor heterostructure nanomaterials,but these methods often require high temperature,high pressure,atmosphere protection and complex operation such as harsh reaction conditions and equipment,which greatly limits the development of metalsemiconductor heterostructure nanomaterials.In this paper,Based on growth kinetics,anisotropy of nanocrystals and the mechanism of solution-liquid-solid?SLS?growth as a guide,a simple polyol method was developed to prepare metal-semiconductor heterostructure nanomaterials by "three-step".Compared with the above methods,the polyol method has a great advantage in the preparation process,such as simple operation,mild reaction conditions,low equipment requirements and environmentally friendly,and thus become effective strategies for preparing different inorganic nanomaterials.Finally,this thesis mainly studies the controllable synthesis of bismuth-based metalsemiconductor heterostructure nanomaterials,and characterizes the structure and morphology of bismuth-based metal-semiconductor heterostructure nanocrystals.We discussed the mechanism of the nucleation and growth of metal-semiconductor heterostructure nanocrystals in liquid.The main contents of this thesis are as follows:?1?A uniform half empty and hollow Bi nanospheres were obtained by introducing a small amount of Fe³⁺ by a polymer-assisted polyol method with an average size of 280 nm and 160 nm,compared to the Bi nanospheres prepared without the addition of Fe³⁺ made its size become more uniform.Especially the introduction of Fe³⁺ formed the half empty or hollow nanospheres,is dependent on the inter-metal Kirkendall effect.During the experiment,Bi nanospheres with different sizes and degrees of space can be controlled by controlling the mass of polyvinylpyrrolidone K30?PVP?,the molar ratio of Bi and Fe³⁺,and the respective concentrations in the polyol system.?2?Through a two-step polyol method,lead chalcogenides PbE?E=S,Se,Te?nanosheets were synthesized with glucose and polyvinylpyrrolidone K30?PVP?as auxiliary.The first stage prepared the uniform morphology of Pb nanoflowers,the second stage further formed PbE stacked nanosheets.It found that the synthesis of twodimensional PbE stacked nanosheet has a larger surface area,thickness of about 40 nm,with regular geometry and shape.?3?Bi-FeS,Bi-CuS₂ and Bi-CoS heterostructure nanomaterials were successfully prepared by "three-step" method using simple solvothermal method.In particular,in the case of ensuring that the "first step" Bi source and the "second step" M source?M = Fe,Cu,Co,Ni source?,the "third step" it is shown that the excess of S source can obtain BiFeS-Bi₂S₃ heterostructures,ternary Cu₃BiS₃ and Ni₃Bi₂S₂ nanomaterials.Based on the analysis of experimental phenomena and results,the growth of bismuth-based metalsemiconductor heterostructures should follow the solution-liquid-solid?SLS?growth mechanism.?4?Bi-PbE?E=S,Se,Te?heterostructure nanomaterials were successfully prepared by the "three-step" experimental method.For the synthesis of typical Bi-PbS heterostructure nanomaterials,the experimental results show that by changing the reaction time of vulcanization,the amount of S source in the vulcanization process,the amount of Bi source and the concentration of each reaction parameter,has an important effect on the morphology of the "match-like" Bi-PbS and the aspect ratio of the rod.In addition,spherical Bi-PbSe and "star-shaped" Bi-PbTe heterostructure nanomaterials were also obtained.Finally,the possible formation mechanism of Bi-PbE?E = S,Se,Te?heterostructure nanomaterials is described qualitatively.