Study On The Synthesis And Properties Of Semiconductor Colloidal Particles And Composite Microspheres

Semiconductor colloidal particles as building blocks can be applied to fabricate novel functional materials according to their special light and electric properties. As for the preparation of semiconductor colloidal particles and composite microspheres, the simple, green, low cost and scalable synthetic system are highly required by the potential application in traditional and novel industry. The particle size, morphology and aggregation can be well tuned by changing the reaction parameter and the particle could have excellent disperibility in green solvents such as water. Moreover, some special colloidal particles which can not be prepared conveniently through traditional synthetic methods could successfully obtained by simple reaction procedure.1. Over past decades, highly monodisperse and water-soluble colloidal nanocrystal clusters have been the object of intensive scientific and technological interest. However, the assembly of nanocrystals in a facile manner into advanced secondary structures with continuous size tuning remains a significant challenge. The formation mechanism also needs to be detailed discussed. So the poloyl such as diethylene glycol has high boiling point, permittivity and good stability, was chose for synthesis of colloidal nanocrystal clusters with controllable particle size.ZnO colloidal nanocrystal clusters (CNCs) have been one-pot synthesized through poloyl mediated high temperature hydrolysis reaction. The particle size can be tuned from 60nm to about 180nm by changing the volume of NaOH in the reaction system due to more OH- could accelerate the hydrolysis of metal cation. We further synthesized monodisperse PbS CNCs under similar condition based on ZnO CNCs. The molar ratios of lead cation to thiourea have great effect on the particle size of product. The formation mechanism of colloidal nanocrystal clusters has also been discussed. PbS nanocubes of ~27nm can be obtained by varying the reaction parameter, and they can disperse stably in water for a long time. The PbS nanocubes and CNCs with different size lead to the different absorption spectra in UV, visible and near IR area. Moreover, the very uniform and highly charged PbS CNCs form periodic structures with regular interparticle spacing of a few nanometers according to the different particle size so that the system strongly diffract light. They are the simplest photonic crystals only in particular directions. The key point in our synthesis is to use poly(acrylic acid) as the surfactant. It shows very strong coordination of carboxylate groups with metal cations, and the uncoordinated carboxylate groups on the polymer chains extend into aqueous solution conferring upon the particles a high degree of dispensability in water. An additional benefit of uncoordinated carboxylate groups is to provide conjunction points for further attachment of other materials.2. There are several oxidation states for some special transition metal, these transition metal usually have poor solubility, easy to hydrolyze and very sensitive to pH value, so it's very difficult to obtain the pure metal with tunable size or morphology by controlling the reaction procedure. In this paper, we developed two kinds of synthetic methods to prepare metal vanadium oxide colloids with tunable particle size. The products have excellent optical or catalytic properties, and can be applied in relevant areas. Monodisperse vanadium oxide colloids such as V2O5, V2O3 and VO2 colloids spheres have been successfully prepared though facile reduction method by hydrogen. The particle size can be well tuned between 200~500nm. The reversible phase transition of VO2 colloids spheres at about 68oC from low temperature monoclinic to tetragonal phase at high temperature is detailedly discussed. The obvious changes of optical property in visible region before and after the phase transition have been monitored by VU-vis absorption spectra. The result shows that these VO2 colloids spheres have high phase transition efficiency and their optical properties are highly related to the particle size. The simulation of the experimental results indicates that the experimental data are agree well with the theoretical simulation. The product could be a promising candidate for potential applications in optical switching devices, temperature-sensing devices and optical data storage medium.3. Multifunctional colloids have been successfully prepared by doping QDs, magnetic nanocrystals or catalyst into silica or polymer beads. Considering their extensive biological and medical application, the facile, green and scalable synthetic methods are required, high loading of functional nanocrystals are also very important. In the paper, we introduce the so-called"surface protected etching method"to render the silica shell of Fe3O4@SiO2 microspheres porous structure. The UV-Vis spectrometry is used to monitor this process by measuring the transmission of the solution because of the original solution becomes more and more transparent with the prolonged etching time. Unlike the traditional methods, the QDs are directly grown within Fe3O4@SiO2 beads, and produce dual-functional microspheres with a series of single light, high loading and high quantum yields. The porous shells also act as physical barriers preventing the aggregation of the particles in the reaction. There were a few references reported recently that incorporation QDs into silica or polymer beads, unfortunately, the potential application to biological field was limited by size of these microspheres and the preparation method, the particle size is too large, the existing method have some trouble with low loading capacity, fluorescence quenching and low quantum yield of QDs. Moreover, ollow silica sphere with mobile magnetic cores were also successfully fabricated. The porosity of the shell can be conveniently tuned by the extent of etching time, thus providing a possibility to control the diffusion of molecules through the shell according their sizes. The method described here is therefore expected to find use in important application areas such as drug delivery and biological sensing.