Synthesis And Properties Of Selenium Compound Nanomaterials （CdSe, Bi₂O₂Se, KCu₄Se₈）

Metal selenide nanomaterial is an important class of semiconductor materialswhich have a series of outstanding chemical and physical properties. They may exhibitdifferent properties according to the type of element component, structure, dimensions,and morphology. Therefore, the application of metal selenide is also very broad, such assolar cells, light sensors, thermoelectric generation and refrigeration, nonlinear opticalmaterials and optical catalysis. In this paper we select CdSe, Bi2O2Se and KCu4Se8these three selenide nanomaterials for the study, with the aim to explore new methodsfor researching the synthesis of the micro-and nano-scale metal selenide materials, andto improve and develop the composite hydroxide media (CHM) method and compositemolten salt (CMS) method, and to expand the scope of these two synthesis methods. Inthis paper we synthesize CdSe, Bi2O2Se and KCu4Se8nanomaterials and study theproperties of photoelectric, thermoelectric and supercapacitor. The main contents of thispaper can be summarized as follows:Cadmium selenide (CdSe) nanorods are synthesized by the modified compositehydroxide mediated approach, and the length and diameter of the nanorod are1μm and200nm. The photoelectric device is fabricated by the CdSe nanorods. The photoelectriceffect of the device is investigated with a simulated sunlight as the light source, and thedevice is tested by I–V curve, photostability, relationship between photocurrent and lightintensity, relationship between photocurrent and electric field, response speed, andreproducibility. The results display that the device has a high sensitivity to visible lightand has a good stability. The response time is in the millisecond range which indicatingthat the device has potential applications in an optical switch and an optical sensor.Cadmium selenide (CdSe) micro/nanowires are synthesized in ethylenediaminesolution at temperature of180°C and the subsequent thermal treatment in N2at400°C.The obtained products are characterized by XRD, SEM, TEM and EDS. The size of theobtained CdSe wires can be controled with lengths from80-150m to3-4m and thediameters from3-5m to200-300nm by adding a proper amount of water in thesynthesis process. A device with one CdSe microwire is fabricated and itsphotosensitivity is systematically studied by a simulated sunlight at room temperature.The methods include I-V curves, reproducibility, response speed and photocurrentversus light intensity. The results show that the photocurrent response of the light sensor based on one CdSe microwire is reversible and periodic, and this sensor displays highsensitivity to light switch, which is in millisecond range, showing the great potential ofthe photoelectric sensor applications.Bismuth oxiselenide (Bi2O2Se) nanosheets are synthesized by thecomposite-molten-salt approach at200C. FE-SEM, XRD and EDS are used tocharacterize this structure, morphology and composition. The results show that theproduct is pure tetragonal Bi2O2Se nanosheets with thickness of120nm. The sample forthermoelectric property measurements is prepared using cold pressing method. Thethermoelectric property of the sample is studied from300K to470K, and themeasurement includes electrical conductivity, Seebeck coefficient and thermalconductivity. The results show that the sample exhibits n-type semiconductor behaviorwith low thermal conductivity (κ300=0.346Wm-1K-1, and κ470=0.458Wm-1K-1). Thehighest figure of merit ZT=0.73×10-2is obtained at460K, although a small figure ofmerit is obtained, but it increases with increasing temperature.The new ternary alkali metal copper chalcogenide KCu4Se8nanowires withaverage length of30μm are synthesized using a modified composite-hydroxidemediated (M-CHM) approach. The prepared KCu4Se8is characterized by XRD, EDS,FESEM and TEM analysis. The structure is determined by the Rotation ElectronDiffraction method. It is identified to be a body center tetragonal phase. The preparedKCu4Se8is used to fabricate solid-state supercapacitors in which the thin film of theelectrodes are made with pressure of0MPa,5MPa and10MPa, and theirelectrochemical properties are tested. It is found that0MPa supercapacitor displays thebest electrochemical performance and the specific capacitance of25.3F/g is obtained atthe scan rate of5mV/s. It also shows good long-term cycle property by recording5000cycles of galvanostatic charge/discharge operation. The specific capacitance can beenhanced to93.7F/g at the scan rate of5mV/s by coating0.1mg V2O5nanowire on0MPa KCu4Se8electrode.