Controllable Synthesis And Optical Properties Of ZnO Quantum Dots–based Hetero-structures

Semiconductor hetero-structures nanomaterials are widely used in a variety of field, such as optical detection, photo catalysis and solar battery, and so on due to their unique physical and chemical properties. In this paper, hetero-structures were prepared via ZnO qusntum dots growing on different nanobelt, and their optical properties were studied. In addition, CuS, as an important II-IV semiconductor, is widely used in areas such as energy storage device. CuS flower micron-structures were successful prepared by hydro-thermal method. Charge and discharge operation of CuS electrode was tested on electrochemistry method. This novel Cu S flower micron-structures might be used in super capacitor in the future.The main contents and conclusions of this paper are as follows:(1) CdS/ZnO hetero-structure and its optical property. CdS/Zn O hetero-structures are synthesized via two-step method. CdS nanobelt was prepared by thermal evaporation method at first. And then, ZnO quantumdots grew on surface of CdS nanobelts by thermal decomposition of Zinc acetate solution. The size and distribution of ZnO quantumdots on CdS nanobelts were controlled by experimental parameters(Concentration of zinc acetate solution, temperature and time). The morphology and structure of the obtained samples were characterized by X-ray diffraction(XRD), field emission scanning electron microscope(FESEM), and transmission electron microscopy(TEM). The photo-luminescence(PL) spectroscopy of hetero-structures at room temperature reveals two peaks at 508.95 and 699.69 nm, corresponding to their intrinsic and defect luminous respectively. The intrinsic emission band gets stronger and the defect emission band gets weaker in PL spectrum of CdS/ZnO heterosyructures, and shift toward lower frequency. Two Raman peaks at 299.11 and 601.97cm-1 of the CdS/ZnO hetero-structures shift toward high wave number. The results show that the energy band structure of nanobelts were controlled through the construction of hetero-structure.(2) The photo-catalytic property of CdS/ZnO hetero-structure. Photo catalytic activity was tested via 10mol/L rhodamine B(RB) degradation as the model reaction. The first and second degradation rates were 97.62% and 93.18% respectively. Compared with the CdS nanobelts, which the first and second degradation rates were 89.94% and 80.01%, CdS/ZnO hetero-structure exhibits enhanced photo catalytic activity in the decomposition of RB under UV-vis light. Further, the effect of zinc acetate concentrations, thermal decomposition temperature and time on photo catalytic performance. This show that the range of optical spectral response was extended by ZnO quantum dots, and the electron of CdS nanobelts was effectively transferred to the ZnO conduction band, achieving effective separation of photoproduction of electron- hole pairs. Therefore, the photo catalytic activity was improved.(3) ZnS/ZnO hetero-structure was controllable prepared by thermal decomposition of Zinc acetate solution on the ZnS nanobelts. The samples were characterized and analyzed by XRD, EDS, FRSEM and TEM. Further, the PL spectra were used to study the optical properties of ZnS/ZnO hetero-structure.(4) The CuS flower-like structures were prepared by a facile hydro-thermal method using copper nitrate and thiourea as starting materials. The electrochemical properties of CuS flower-like architectures were investigated for super capacitor applications. The growth mechanism of CuS flower-like architectures was analisised with the field-emission scanning electron microscope. The result shows that the formation of CuS flower-like structure due to the aggregation of CuS nanoplates, and its average size is about 2 um. Electrochemical property such as cyclic voltammetry, long-term cyclic stability and electrochemical impedance spectroscopy were studied. The CuS electrode shows a specific capacitance of about 170.948 F /g from the cyclic voltammetry at a scan rate of 5mV/s. CuS flower-like structure has higher specific capacitance and cycle stability compared with the same material reported in the literature.