| Hollow spheres with nano-and micro-sizes, as a special class ofmaterials, have attracted much attention, because of diverse applications,including catalysis, drug delivery, electric magnetic absorption, chemicalsensors, structural materials, and so on. The template method is the mostcommon for the synthesis of hollow structures. In general, the templatemethod includes hard, soft and sacrificial template strategy. Hardtemplate-based strategy has been regarded as a very effective method forthe synthesis of hollow structures; however, it has intrinsic shortcomings,which include the complicated multi-step processes, high cost, difficultiesfor removal of the templates. Compared with the hard template route, softtemplate-based strategy has many own advantages, such as simpleprocedures (especially one-pot synthesis), variability of the templatesources, and easy removal of the templates by washing. Usually, thesesoft template routes must make use of the gas or liquid particles(surfactant micelles, bubbles, microemulsion droplets and so on) asreactive precursors or need the adsorption of the particle surfaces for areactant, and then the reaction can occur at the surface of the templates,leading to the formation of hollow spheres. Sacrificial template strategyneeds a specific template that is a reactant or intermediate. However, allof these template routes must use the templates as reactive precursors orneed strong physical or chemical interactions between the surfaces oftemplates and the reactants. So the application of these routes will belimited by the difficulty in preparing different hollow spheres.We presented a novel template-interfacial-reaction route for thepreparation of hollow spheres in this dissertation. In this way, hollowspheres could be obtained directly since the reaction of two reactantsrespectively dissolved in two different phases of a two phases systemonly occurs at the oil/water interface. By changing the reactants in the two phases, different hollow spheres can be prepared. Neither a reactivetemplate nor the interactions between the oil droplets interface and areactant is needed. Therefore, our approach solves the common problemthat fabrication of different hollow spheres needs diverse templates, andis a versatile method for preparing hollow spheres. Based on this idea,difference hollow spheres and novel nanostructures have beensynthesized in the microemulsion two phases system. The main contentand conclusions of this thesis are described as follows:(1) Nano-size CuS hollow spheres have been successfully synthesizedthrough a facile microemulsion-template-interfacial-reaction route. Theaverage diameter of the CuS hollow spheres can be adjusted from110to280nm by changing the content of oil phase. Based on the study of theformation mechanism of the CuS hollow spheres, it can be conclude thatthe reaction conditions that can control interfacial reaction rate areimportant factors for forming hollow spheres. Therefore, it is a key forforming hollow spheres to ensure the growth of the nuclei on the interfaceby controlling reaction conditions to optimize the interfacial reaction rate.In addition, the two-phase method experiences a much longer andrelatively slow nucleation and growth process. The poorly crystallizedCuS aggregates (or poorly crystallized hollow spheres) composed of CuSnuclei can be obtained at a low temperature in a two phases system andthen grow into the nanoplate-based hierarchical CuS architectures (orhierarchical hollow spheres) through a recrystallization growth process ata higher temperature.(2) The SiO2hollow spheres and nanowires have been obtained in amicroemulsion system. The morphology of SiO2is determined by themass ratio of TEOS to Dimethylbenzen. When the mass ratio of TEOS toDimethylbenzen is1:3, the products are nanowires composed ofnanoparticles with a mean diameter of70nm. This is probably becausethat the cagelike nanoparticles self-assemble into the nanowires due to theguidance of the surfactant and the trend of convergence of internal liquidTEOS. When the mass ratio of TEOS to Dimethylbenzen is1:1, thehollow spheres with the diameters ranging from0.5to1μm can beobtained. The formation of hollow spheres is dependent on the template of oil-water interface. It is a key for forming hollow spheres to properlyincrease the hydrolysis and condensation reaction rates of TEOS bycontrolling reaction conditions. Therefore, the appropriate increasing theconcentration of ammonia and the reaction temperature are conducive tothe formation of hollow spheres.(3) Ni hollow spheres with an average diameter of about100nm havebeen successfully synthesized through a microemulsion-templateinterface-reaction route using nickel naphthenate as metal precursor andhydrazine hydrate as reductant. The results show that excess surfactant isnot conducive to the formation of nickel nuclei.(4) SiO2hollow spheres and nanowires have a good adsorptiveproperty for methylene blue. The adsorption capacity and rate of the SiO2hollow spheres is much higher than that of the SiO2nanowires.Adsorption isotherms of MB on silica hollow spheres and nanowiresaccord with Freundlich equation. The adsorption capacities of the SiO2hollow spheres and nanowires for MB are64.52mg/g and50.66mg/g,respectively. Moreover, the SiO2hollow spheres and nanowires exhibitsuperior adsorption capacity over multi-shelled mesoporous silica hollownanospheres (25mg/g) and the silica absorbent prepared by sol-gelmethod (33.3mg/g) in the literatures. The changes in standard freeenergy of the SiO2hollow spheres and nanowires are less-20kJ/mol,which indicates that the adsorption of the SiO2hollow spheres andnanowires is physical adsorption.(5) The absorption spectrums of the hierarchical CuS show anincreased absorption in the near-IR region, which is the characteristicband for covellite CuS. However, the characteristic absorption band ofCuS is completely absent in the poorly crystallized CuS. The band gapsof the different morphologically CuS are to some extent larger than thereported value for bulk CuS (Eg=1.85eV), because of small size effect.The as-prepared CuS with difference morphology exhibit highphotocatalytic activity for the degradation of methylene blue in thepresence of hydrogen peroxide under natural light. About90%of the MBwas degraded after40min, and the hollow spheres exhibit superiorphotodegradation efficiency over solid structures. In a word, the template-interfacial-reaction route is a versatile softtemplate method for preparing hollow spheres. Different hollow sphereshave been successfully synthesized by changing the reactants in the twophases. Furthermore, it is proven that our approach is applicable todifferent interfacial reactions. If diverse the morphologically oil/waterinterfaces, such as cylindrical interface of cylindrical microemulsions, areused as the templates, the other hollow nanostructures with differentmorphologies should be fabricated. So this approach will expand theapplication of microemulsions and two phase system in the preparation ofnanomaterials. |
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