Preparation And Shape Modulation Of Hybrid Nanoparticles In Water-in-Oil Emulsions

The structural design and controllable preparation of hybrid nanomaterialsfor the purpose of obtaining expectant properties is a focus of research inmaterials science. Hybrid nanomaterials can display the advantages of eachcomponent, furthermore give significant play to their cooperative advantages dueto the hybridization between their components. Hybrid nanomaterials hence havevaried functions and can be used for both constructional materials and functionmaterials, and have a vast range of prospects for applying. Semiconductor hybridnanomaterial is a typical and important kind of hybrid nanomaterial, it hasattracted considerable attention from physicists, chemists and materials scientists,and metal/semiconductor composite nanoparticles have been applied in catalyst,electronic devices and so on due to the possible interactions between metals andsemiconductors in the particles and the researches on their preparation andproperties have aroused general interest. Zinc sulfide is a fine semiconductormaterial with some characteristics such as infrared transparency, fluorescence andphosphorescence, and has been extensively used in sensors, high resolutiondisplays and electro luminescence materials and so on. The properties of ZnSnanomaterials are dependent to particle size and distribution of their particles aswell as their morphology to a great extent, thus it is a key to control these factors. There are many methods of preparing hybrid nanoparticles, which have theirrespective features. For example, the preparation of metal/semiconductorcomposite nanoparticles needs to tread the interface relations between metals andsemiconductors, which generally are achieved by modifying the surface polar ofmetals using an appropriate coupling agent, and the experimental proceduresgenerally are overelaborate;Inverse emulsion technique is a new preparationtechnique, which uses non-polar media as a continuous phase, and waterdissolving reactants as a dispersed phase to form isolated very fine aqueous cellsas a micromicelle reactor or nano-reactor (or aqueous core called). Inverseemulsion technique is a simple, fast and effective method for preparing variouscharacteristic nanomaterials by designing and adjusting the reactionmicroenvironment, and open up a new way to prepare new materials.In this dissertation, we first report the structural design and controllablepreparation of Ag/TiO2 hybrid nanoparticles for the purpose of obtainingexpectant properties by use of the reduction of Ag+ in water phase and thehydrolysis of Ti(OC4H9)4 at the water/oil interface in water-in-oil emulsions.Ag/TiO2 hybrid nanoparticles with core-shell and strawberry-like structures wererespectively obtained by the use of the special interfacial properties in inverseemulsions under the optimized experimental conditions. The chemicalcomponents, morphology and photo-electric properties of the Ag/TiO2 hybridnanoparticles were characterized with TEM,IR,TG-DTA,XPS,XRD and SPS.The phase transformation of TiO2 from anatase, a crystal phase with catalyticactivity, to rutile usually occurs at 500-600℃. However, in our experiments, bothTiO2 and Ag@TiO2 nanoparticles prepared in the same system of inverse emulsionkept their anatase structure after calcinations at 700℃ for 4h. This observationopens up new possibilities for the application of photocatalysis over a widertemperature range. The effect of preparation methods on the phase-transformationtemperature of TiO2 from anatase to rutile needs further investigation. The resultsof Raman spectra indicated that the Ag/TiO2 hybrid nanoparticles withstrawberry-like structure are a surface-enhanced Raman scattering active medium.It is essential for controlling morphology of hybrid nanoparticles by usingconfinement and channel effect of water-soluble polymers in inverse emulsions oninorganic reactions to construct a stable inverse emulsion containing polymers.The stability of inverse emulsions can be usually adjusted though controllingexperimental conditions such as regulating oil/water ratio, emulsifiers and so on.The complication of constitution in an inverse emulsion containing polymersdecides the complication of the factors influencing their stability, and it is not onlydifficult to obtain a stable inverse emulsion containing polymers but go so far asto result in a phase inversion, if only some one factor is considered simply. Thus,the stability and phase behavior of acrylamide-based emulsions, prepared withsurfactants consisting of lipophilic Span80 and hydrophilic OP10, before and afterpolymerization were investigated. The research results two kinds of phaseseparation mechanisms caused by the ratio of toluene to water and an equivalenceprinciple of acrylamide concentration and HLB value. When the water volumefraction was larger, the phase separation mechanism was mainly a penetrating ofaqueous molecules from the dispersed phase droplets. When the water volumefraction was smaller, the phase separation mechanism was mainly sedimentationof the separated aqueous droplets. At a fixed toluene /water ratio, the emulsionstability and the emulsion type do not only relate to the ratio of the two surfactantsbut also to acrylamide concentration, and the effect of increasing acrylamideconcentration on character of the emulsions is similar to that of increasing OP10mass fraction (increasing HLB value), which determines the correspondingrelationship between acrylamide concentration and HLB value in the most stableemulsion system. In order to obtain the most stable emulsion at a fixed acrylamideconcentration, the emulsion with higher acrylamide concentration needs lowerHLB value for the emulsion systems. This work laid a foundation for optimizing arecipe of a stable acrylamide-based emulsion by controlling these factors.On the basis of the above research on the stability of the acrylamide-basedemulsions, ZnS nanoparticles with various shapes were prepared in variousinverse emulsions containing polyacrylamide(PAM) and the formation mechanismof ZnS nanoparticles was investigated. The morphology of ZnS nanoparticlesprepared in this series of water-in-oil (W/O) emulsions was studied with TEM andXRD, and their photoelectric characteristics were characterized simply withphotoluminescence spectra and surface photovoltaic spectroscopy (SPS)measurements. The research results indicate that not only the PAM template butalso the precipitating agents (Na2S or H2S) can have an effect on the modalities ofZnS nanoparticles. The method developed in this work, based on the confinementand channel effect of the water-soluble polymer in an inverse emulsions on theinorganic reactions, can achieve success in controlling the morphology of ZnSnanomaterials in the various designed polymer templates by using differentprecipitators. The thermal stability of ZnS/PAM composite microspheres has anobvious increase, compared with the PAM microspheres. The hybrid materialswith a core-shell structure of the ZnS nanoparticles coated by PAM have potentialapplications in fluorescence and electroluminescence materials.In summary, some novel semiconductor hybrid nanoparticles were preparedby inverse emulsion technique in this dissertation, and the results obtained by thesystematic study in the dissertation have revealed the feasibility for thecontrollable preparation of the semiconductor hybrid nanomaterials by the use ofinverse emulsion technique.