Preparation And Application Of Some Metal-oxide And MoS₂ Nanomaterials

Metal oxide semiconductor nanomaterials show the great value in photovoltaic, catalysis, gas sensing and fluorescent biomarkers. MoS₂ nanostructures in aerospace, new energy and other fields have broad application prospects. In order to study the physical properties of nanostructured materials, the morphologies and growth mechanisms of the nanomaterials were analyzed by the traditional method. Then, their applications in light, field emission, sensor and catalytic were alsoemphatically investigated in this paper. The main research content and innovation points are as follows:1. Synthesis and characterization of metal-oxide semiconductor and MoS₂ nanomaterials. The ultra-long tetrapod-like, sea-urchin-like, network ZnO micromaterials and were synthesized by a conventional thermal evaporauon method. The SnO2, In2O₃ nanowires and nanobelts were also synthesized by thermal chemical vapor transport method. The obtained samples were characterized by SEM, TEM, and XRD. The ZnO network structure is formed by a large number of nanorods, which has a high surface-to-volume ratio, easy to adsorb gas molecules and water molecules. Moreover, on the basis of literatures, we analyze the growth mechanism of the products. In addition, we have prepared flower-like, spherical and porous MoS₂ nanostructures by hydrothermal method. The samples were characterized by SEM, XRD and TEM, and showed the high purity. We think that the MoS₂ crystal nucleus was formed in the hydrothermal reaction at first. Due to the difference of free energy on the surface of the crystal, the MoS₂ crystal nucleus would grow along the preferential direction, and formed the nanosheets and the nanoparticles in different conditions. Subsequently, in order to reduce the surface energy, these nanosheets or nanoparticles in the solution aggregated self-assembly, and formed flower-like and spherical nanostructures ultimately.2. Application of metal-oxide semiconductor nanomaterials in the light and electric field. The obtained ZnO samples were investigated by photoluminescence ?PL? spectra.The ultralong tetrapod-like ZnO microstructures with good crystal had a dominant near-band-edge emission. But the ultralong ZnO network structures had much more surface defects, leading to that the green deep level emission was dominant. In addition, the ultralong ZnO microbelt and silver electrode formed good ohmic contact by hydrogen plasma treatment. It can be found that the Cu₂O nanoparticles were covered on the surface of ZnO microbelts formed the n-ZnO/p-Cu₂O heterojunction. Under a direct-current voltage excitation, surface-emitting lasing actions of ultraviolet and blue random laser emission were observed at room temperature. The field emission properties of SnO₂ nanowires and nanobelts were studied. The Field emission results demonstrate that the SnO₂ nanowires possess good performance with the turn-on field of 2.37 V/?m, the threshold field of 4.21 V/?m and the field enhancement factor of 3237, and have a potential application in FE-based flat panel displays.3. Application of metal-oxide semiconductor nanomaterials in the sensor. Because of the low resistivity, In₂O₃ nanomaterials were often used in gas sensors. In this paper, the humidity properties of were first studied. At relative humidity of 97.2% of the environment, resistance of In2O₃ nanobelts was 5.13 x 10³ ?, and the sensitivity is about 77. The response time and recovery time were 30 s and 45 s. Finally, we give some discussions about the hysteresis phenomena of the humidity sensor. Moreover, the humidity sensing properties of bottlebrush-like ZnO nanostructures were investigated in different static air of relative humidity ?RH? at room temperature. The sensor based on ZnO nanobushes showed rapid response and recovery, prominent stability, and good repeatability. A new type sensor based on the Sn doped ZnO microrods with lots of burls were fabricated for the ethanol gas. For ethanol gas at levels of 10,50,100,500 ppm, the sensitivities of the sensor were 9.5,35.6,52.4 and 104.2, respectively. The response time and recovery time were about 10?30 s and 25?55 s, respectively. Then we describe theoretically the origin of the high sensitivity with the grain boundary barrier model.4. Application of MoS₂ nanomaterials in catalysis. The three different structured MoS₂ including flower-like, sphere and porous as electrocatalysts for hydrogen production. Due to its unique structural feature with densely attached MoS₂ slices that could provide highly exposed edges as active sites, the flower-like MoS₂ with low onset of 125 mV and Tafel slope of 89 mV/decade exhibited the highest hydrogen evolution reaction activity. In addition, the first-principles investigation based on density functional theory was further performed to survey the adsorption characteristic of H atom in MoS₂ at different sites, which enriched the understanding of the mechanism of MoS₂ hydrogen evolution reaction.