Study On The Preparation And Properties Of Bismuth Sulfide And Its Composites

As a direct band gap semiconductor, bismuth sulfide (Bi2S3)has many excellent properties. Bi2S3 belongs to orthogonal crystal system and its band gap is of 1.2?1.7 eV. It can cause blue shift of fluorescence emission and absorption wavelength, increasing the capability of oxidation reduction of nanoparticles. It has good photocatalytic activity and potential applications in thermoelectric, electronic and optoelectronic devices. There are two factors to eventually decide preferential growth direction of Bi2S3 crystal. One is the layered structure and another is the highly anisotropic.Different morphologies of Bi2S3 nanomaterials have been synthesized, such as a nanoballs, nanorods, nanowires, nanoflowers, nanotubes and nanoflakes.Many synthesis methods have been used for the fabrication of Bi2S3 nanostructures, such as sol-gel method, solvothermal method, microwave method, hydrothermal method, reflux method, sonochemical method, surfactant assisted hydrothermal method, etc.Nowadays, the research on Bi2S3 nanostructures has made great achievements; however, there are still some key technical problems. For example, the relationship between the morphologies and the experimental conditions (such as raw materials, reaction temperature, different substrates) has not yet been systematically studied. How to realize the controlled synthesis of these nano/micromaterials with low cost and temperature is still not mature.There are many factors which can affect the morphologies, and it is necessary to optimize conditions to preparate Bi2S3 nanomaterials with uniform morphologies and sizes.In this thesis, we use hydrothermal method to synthesize Bi2S3 nanostructures and the composites by changing reaction time, concentration of raw materials, different substrates, and study their properties. Then, their morphologies, structures, components, band gaps and luminescence characteristics of the samples are detaily analyzed. The main results are as follows:(1) Bi2S3 micro/nano-structure has been successfully fabricated by hydrothermal. We studied the effect of growth time, solution concentration of Bi (NO3)3·5H2O and different substrates on the sizes and morphologies of samples. When the growth time is 1h,4h,8h,12h at 180?, we found that nanorods transformed to micro-flowers, and the diameter of micro-rods become shorter and shorter with the increase of growth time. When the concentrations of Bi(NO3)3·5H2O are 16 mM?8 mM?4 mM respectively, and the reaction time is 12h, the morphologies of Bi2S3 are kept with the shape of microflowers. Bi2S3 on Al and Ti plates are in the form of flowers and the nanoparticles are formed on copper plates. XRD spectra showthat all diffraction peaks correlate very well with the reference diffractions of a pure orthorhombic Bi2S3 phase (JCPDS no.65-2435), and no additional peaks are observed indicating that no impurities or secondary phases exist. ?-? curves of the sample of 8h,16mM are studied, and the results show that ?-? curve has good rectifying characteristics. Supercapacitor measurements show that the as-synthesized Bi2S3 structures have good charge and discharge effects, and the diffusion resistance and charge and discharge resistance is small. They also exhibit good photocatalytic degradation properties.(2) Bi2S3 and Bi2S3/S microstructures have been successfully fabricated by hydrothermal method. The SEM results show the structures are nanowires. The Bi2S3 microstructures show faster degredation of RhB. The absorption test confirms the bandwidth of Bi2S3 nanowires is about 1.6 eV. Blue shift occurs for Bi2S3 nanowires compared with nanorods; SEM results show the structures are nanorods. From XRD pattern, we know that there is a diffraction peak at 30° for Bi2S3/S nanostructures, proving that the existence of element S. Bi2S3/S nanorods show much faster degredadtion rate on RhB. The absorption test results confirm Bi2S3/S nanorods bandwidth is about 1.4 eV, showing red shift compared with Bi2S3 nanowires;(3) Bi2S3/CdS and Bi2S3/ZnS nanostructures have been successfully fabricated by hydrothermal method.The SEM results show that Bi2S3-CdS nanowires are uniform, and XRD patterns show the as-sythesis Bi2S3-CdS are pure phase. TEM characterizations depict that there are Bi, S, Cd elements, proving prepared Bi2S3-CdS nanowires; Bi2S3-ZnS nanowires have been successfully fabricated by hydrothermal method. Bi2S3-ZnS nanowires are uniform and gather together. XRD shows that peakes on Bi2S3 nanowires are observed, with ZnS direction in (002), proving that generated the Bi2S3-ZnS structure. EDAX image confirms that the generated structure existing Bi, S, Zn element, proving that the generated sample is Bi2S3-ZnS structure.