Synthesis And Microstructure Study Of Ⅱ-Ⅵ Group Semiconductor Nanomaterials And Nanocomposites

As a group of traditional wide-bandgap semiconductors,Ⅱ-Ⅵgroup semiconductor nanomaterials show extensive potential applications in the fields of catalyzing, sensing, optics, magnetism, etc. ZnS has been a kind of widely used wide-bandgap semiconductor material due to the largest bandgap of 3.7 eV at room temperature among all theⅡ-Ⅵgroup semiconductors. As a representative ofⅡ-Ⅵgroup semiconductors, ZnxCd1-xS solid solutions possess tunable bandgaps from ZnS's to CdS's, covering almost the whole visible spectrum. ZnO is not only a semiconductor with excellent properties, but also an antimicrobial and biocompatible material. ZnO/polymer nanocomposite with properties of both ZnO and polymers can be synthesized by diffusing ZnO nanomaterials into polymers.In order to deeply study the relationship between structure and properties and design functional materials according to our desire, it is very important to synthesizeⅡ-Ⅵgroup semiconductor nanomaterials and nanocomposites, explore the growth mechanism and control their dimension, size and properties. For this purpose, systematic studies have been conducted in this dissertation.ZnS nanorod arrays, ZnxCd1-xS nanoflake dendrites and ZnO nanoparticle/PHBV composite fibrous membranes are successfully synthesized in this work and their corresponding morphologies, phases, molecular structures, thermal and photoelectric properties are studied. The main results are listed in the following:1. ZnS nanorod arrays are synthesized by hydrothermal method and the reaction condition in the typical synthesis is much milder than that in the reported hydrothermal reactions. In this work, aqueous solution is only used while the reaction temperature and time are 95℃and 1 h, respectively. The ZnS nanorods grow orderly as arrays on Zn nanocrystals with root diameter of about 30 nm and length of several micros. Control experiments are designed to explore the effect of reaction parameters (reaction time, reagent concentration, pH value of the solution, substrate and so on) on product morphology. Much attention is paid to designing ordered nanostructure-ZnS nanorod array and exploring its growth mechanism. The photoluminescence result shows the ZnS nanorod arrays' potential applications in photoelectric field, e.g., the blue-light-emitting equipments.2. ZnxCd1-xS nanoflake dendrites are prepared by hydrothermal method, using water and ethylenediamine as co-solvent, after a hydrothermal reaction at 95℃for 1 h. The trunk of the ZnxCd1-xS nanoflake dendrite is common dendrite of about 10μm with periodic embranchments on it and the embranchment is consisted of numbers of uniform regular hexagon nanoflakes. Since nanoflake dendrite is a novel nanostructure which has never been reported before, we focus on its growth mechanism. In control experiments, series of solid solutions are synthesized by changing the ratio of Zn and Cd sources in the reagents. Our main aim is to explain the formation of ZnxCd1-xS nanoflake dendrites in the reaction. The UV-vis absorption spectra results of serial solid solutions show that bandgap control of the ZnxCd1-xS nanoflake dendrites is successfully realized in this work.3. ZnO nanopartilces have always been highlighted amongⅡ-Ⅵgroup compound nanomaterials and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is also a representative of polyhydroxyalkanoates (PHAs). There have been few reports on composite of the two. In this study, ZnO nanoparticles are firstly synthesized by a sol-gel method without further modification. Then by a two-step electrospinning method without diffusion additive, ZnO/PHBV composite nanofibrous membranes are prepared.1 wt% ZnO nanoparticles (compared with PHBV) diffuse well in the 4 wt% PHBV (compared with electrospinning solution) electrspun fibers.4. According to FTIR and DSC results, the interaction between the organic phase (PHBV) and inorganic phase (ZnO nanoparticles) is investigated. Hydrogen bonds are formed between hydroxyl groups on the surface of ZnO nanoparticles and carbonyl groups of PHBV, which are the key point for the good diffusion of ZnO nanoparticles in the electrospun fibers. In addition, ZnO nanoparticles have great influence on PHBV's cryatallization behavior, i.e., slowing down the crystallization rate and decreasing the crystallinity of PHBV.