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Synthesis and Properties of the Selenide Compound (Cu2-x Se, ZnSe) Nano/Micro-structure

Author: ZhangYan
Tutor: HuChenGuo
School: Chongqing University
Course: Condensed Matter Physics
Keywords: M-CHM nanowires Seebeck coefficient spherical flowerlike hierarchical structure photocatalytic
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 136
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Abstract


II- VI compound of nano-materials have received great attention due to their wide applications in photoluminescence, laser, waveguide, electro-optic modulator, solar cells, field effect transistors, optical detectors, photocatalysis, nano-piezoelectric generator and other fields. Selenium compound is one of the most important II– VI compounds, it’s widely used in the nonlinear optical materials, light sensitive materials, photocatalytic materials, semiconductor devices, thermoelectric materials and so on. In this paper, we choose Cu2-xSe and ZnSe as the study objects.We have synthesized Cu2-xSe nanowires, ZnSe microspheres via a modified composite hydroxide mediated method and spherical flowerlike hierarchical structure of ZnSe via the ternary solvothermal. Then did some research on their properties. The main results are summarized as follows:①Single crystalline Cu2-xSe nanowires with length up to 50μm were synthesized via a modified composite hydroxide mediated method （M-CHM）, the width of single nanowire is about 200 nm. Experiments reveal that single hydroxide, the quality of composite hydroxide, amount of water and recation time could induce the formation of different morphology.The growth mechanism of Cu2-xSe nanowires has been proposed. The UV-visible-near infrared reflection spectrum demonstrates the optical absorption of the Cu2-xSe nanowires in the ultraviolet and near-infrared region, which could be interpreted in terms of direct allowed transitions with band gap of 2.38 eV and indirect allowed transitions with band gap of 1.12 eV. The nanowires produced by our method have potential applications in solar cells as well as photoelectron device in near-infrared region according to the estimated band gaps. In addition, Seebeck effect based on the Cu2-xSe nanowires was investigated, demonstrating the Seebeck coefficient of 180μV/K. The positive value indicates its p-type semiconductor behavior.②Zinc selenide （ZnSe） microspheres with the diameter of 3μm and ZnSe flower-like microspheres with the diameter of 46μm assembled by nanosheets were synthesized via the modified composite hydroxide mediated （M-CHM） approach using zinc powder and Se powder as the precursor at 200°C for 24 h-48 h. The products were characterized by X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy, UV-visible absorption spectrum. Photocatalytic activity of the ZnSe flower-like microspheres and ZnSe microspheres for the degradation of methylene blue and methyl orange under the irradiation of the simulated sunlight （100 mW/cm2） was studied.③Spherical flowerlike hierarchical structure of ZnSe（en）0.5 had been synthesized via a solvothermal route in the NH3·H2O-ethylenediamine （en）-N2H4·H2O system at 180°C for 24 h. Thermo-gravimetric （TG） and differential scanning calorimetry （DSC） analysis shows that the precursor could be further converted into pure hexagonal ZnSe by annealing in flowing nitrogen gas at 500°C for 1 h, and the geometrical morphology could be well preserved. The spherical flowerlike hierarchical structure is assembled from a host of regular nanosheets with thickness of 20-50 nm, and the size is about 5μm.④The reaction mechanism of spherical flowerlike hierarchical structure ZnSe is discussed. The UV-visible absorption spectrum and PL spectrum of ZnSe spherical flowerlike hierarchical structure were measured. In addition, photocatalytic activity of the ZnSe flowerlike structure for the degradation of methyl orange under the irradiation of the simulated sunlight （100 mW/cm2） was also investigated. The results indicate that the absorption of the typical peaks at 464 nm is almost 0 when irradiation with the simulated sunlight for 9 h.

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