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The Control Synthesis of Nanosilica and CdS@SiO2 Core-shell Nanomaterials in Triton X-100 Reverse Microemulsion

Author: YaoLin
Tutor: XuGuiYing
School: Shandong University
Course: Physical and chemical
Keywords: Iso- butyl phenol polyoxyethylene (10) ether (Triton X-100) Reverse Microemulsion SiO2 CdS @ SiO2
CLC: TB383.1
Type: Master's thesis
Year: 2007
Downloads: 572
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Abstract


In recent years, the size of the micro-nanoscale SiO 2 because it has important applications in the field of catalysis, materials science, electronics, ceramics, chromatography, adsorption, drug transport, thermal insulator, and the date such times attention. In particular, the Advantages Because of SiO 2 , nontoxic, chemically inert, optically transparent and easy surface-modified, it can be blended with other materials or doped forming a composite material having special properties. By SiO 2 wrapped semiconductor nanoparticles has become a hot research field in recent years colloid and materials science. By SiO 2 wrapped semiconductor nanocomposites without wrapped raw materials with improved optical, electrical and other physical and chemical properties, and SiO 2 surface can be easily classic surface chemistry modification, can increase the solubility of the semiconductor nanocrystals in different solvents, to extend its application field. As a novel liquid phase chemical method, the reverse microemulsion method has been used to prepare a variety of nanomaterials. Recently, this method successfully prepared SiO 2 stick by SiO 2 involved in the core-shell structure composite. In particular, this method in the process of preparing the core-shell structure shows significant advantages prepared nuclear material can be prepared, and a silicon shell formed all in a micro-reactor, to avoid surface pre-modification of the nuclear material, the experimental operating simplify. But also by changing the reaction parameters R ([H 2 O] / [Surfactant]), and h ([H 2 O] / alkyl silicate) and the reaction effective regulation of reagent concentration on SiO 2 and core-shell nanoparticle size, size distribution, single-core or multi-core core-shell particles and SiO 2 shell thickness . The papers on the basis of previous studies, the use of non-ionic surfactant Triton X-100 formed inverse microemulsion synthesized SiO 2 nano-particles, and of CdS _AT_ SiO 2 core-shell nanoparticles. The experiment has made certain achievements, inverse microemulsion medium synthetic nanoparticles and core-shell structure of nanomaterials has certain reference value. The thesis is divided into four parts, is briefly described as follows: 1. Introduction detailed description of the process to the inverse microemulsion prepared SiO 2 , by changing the reaction parameters R ([H 2 O] / [Surfactant]), and h ([ H 2 O] / alkyl silicate), the types of surfactant and the oil phase, the co-surfactant agent SiO 2 regulation of particle size and size distribution; addition, by changing the composition of the inverse microemulsion, surfactants and oil phase type of SiO 2 regulation and control of the morphology and microstructure. Improvements the Stober synthesis as well as the inverse microemulsion method detailed summary and comparison, we can see the the inverse microemulsion synthesis because of its simple operation, the core-shell particles can be controlled in the preparation of a variety of nanocrystalline spherical core-shell nanoparticles the size and distribution of benefits has become the method of preparation of core-shell materials in the 21st century, chemists have preferred. In addition, despite the precise and widely applicable methods of the core-shell structure of a single quantum dot is prepared containing a very long way, but has been able by changing the reaction parameters such as reaction reagent concentration or adding other substances SiO 2 the shell wrapped nanocrystalline number control. 2. Triton X-100-based the inverse microemulsion characterization and reaction parameters determine the first to be prepared SiO 2 nanoparticles reverse microemulsion liquid phase diagram drawn, excluding alcohol, the TX- 100 / cyclohexane system inverse microemulsion liquid region is small, will have a significant ability of solubilizing aqueous phase, only when about 20% of the mass fraction of the TX-100 in cyclohexane. When ammonia is used as the aqueous phase, the the reverse microemulsion liquid region larger than the use of the three phase region distilled water as the aqueous phase. With the increase of the ammonia concentration, the the reverse microemulsion liquid region is gradually increasing. Adding alcohol, compared with no alcohol, the reverse microemulsion liquid region increased significantly. Under normal circumstances, with the alcohol chain length increases, the the inverse microemulsion liquid region to expand. Containing the Hexanol microemulsion liquid region when the mass fraction of the mixture (surfactant alcohol) in the range of 56-80%, the ratio of n-amyl alcohol-containing microemulsion liquid area. And when the mass fraction of the mixture is larger (about 80-90%) of the stars phase variation, the appearance of the system does not appear that the inverse microemulsion after bicontinuous phase directly converted to an O / W microemulsion. On the analysis of the phase diagram, and the basis of the consideration of other factors, we select the TX-100 concentration of 0.3mol / L. Does not contain alcohol, R is 0.5, 1 and 2, when the system contains an alcohol, we choose a 14.2% aqueous ammonia as the aqueous phase, R is 2,4,6,8,10,12 and 14. Does not contain alcohol, the conductance value of the system is small, less than 1μs · cm -1 . Particularly when R is 0.5, due to the detection limit of the conductivity meter smaller the conductance value detected no system, the displayed conductivity value is zero. For all the ammonia concentration, with the increase of R, the conductance value is first gradually increased, reaching a R value (4) increased dramatically, indicating the occurrence of phase separation. In the same R-value, the conductivity is increased with the increase of the concentration of ammonia. Containing alcohol, the changes in the conductance of the system is very interesting, with the increase of R, has experienced a steady increase and after the significant increase in the area, conductivity begins to decrease. When R is less than 12, with the alcohol chain length increases, the conductance value is reduced. This is because the alcohol chain length is longer, the greater the interface strength. When R is greater than 12, the micro-emulsion containing n-octanol having a maximum conductivity value. This is because then the inverse microemulsion containing octanol closest to the phase transition. The reverse micelle system excluding the alcohols, as R is increased until the phase separation, the methylene blue MB maximum absorption wavelength λ max has been increasing, indicating that the absence of free water in the reverse micelles. Reverse micelle system containing alcohol, with the increase of R, the beginning of λ max gradually increased until R 6:00, after λ max remain unchanged, suggesting that reverse micelles no longer change the water in the nuclear environment. When r is 6, the reverse micelle kernel consisting of water, the nature of the free water is similar to the bulk water. Than triple distilled, CdCl , 2 aqueous solution as the aqueous phase the reverse microemulsion liquid region the size of the impact is not obvious, the reverse microemulsion liquid region only slightly expanded. And with CdCl 2 of increasing concentrations of, microemulsion liquid region is only slightly increased. The comprehensive experimental conditions, we choose the surfactant mixture in cyclohexane for the mass fraction of 40%, the initially added CdC1 2 mass fraction of 8%, to study the influence of the starting water produced particles when starting added CdC1 2 mass fraction of 4%, 8% and 10%. 3. Triton X-100 (the positive alcohol) / cyclohexane / ammonia system nano-SiO 2 control of size and morphology of the synthesized using TX-100, the oil phase of cyclohexane, ammonia water phase SiO 2 nanoparticles and catalyst, prepared in reverse microemulsion investigated R spherical particle size and size distribution of ammonia concentration and positive alkanol chain length (5,6,8) adjusting the reaction parameters impact; still stirring synthetic fibrous SiO 2 , and propose a possible reaction mechanism. Excluding alcohol, 2 size was unchanged or downward trend in the first sharp increase as R increases, the average particle size between 15-60 nm; containing alcohol obtained spherical an SiO the spherical SiO 2 average particle size of 40-80 nm the SiO 2 size with the trend of R with alcohol-free situation is the opposite; does not contain alcohol spherical SiO 2 the size distribution of 12%. Containing alcohol, of SiO 2 the size distribution of between 4-16%, and the distribution with the increase in size of R increases first and then stabilized with the proximity of phase separation and showed an increasing trend. Excluding alcohol, When R is 0.5, as the ammonia concentration increases an SiO 2 size gradually increases; When R> 1, with the increase in the ammonia concentration of SiO 2 size of the minimum value of 8.94% of the ammonia concentration. Alcohol chain length for the the spherical SiO 2 2 general downward trend; close to the phase separation, the largest alcohol chain length SiO 2 Size the largest. As the alcohol chain length increases, SiO 2 size distribution of the changes is similar; SiO 2 size distribution close to the phase separation, the largest alcohol chain length is the maximum 's. Does not contain alcohol, the spherical morphology of the particles is not very regular. As R increases, the smoothness of the surface of the particles and dispersion properties have been improved, and this situation is more evident in the low ammonia concentrations. When cosurfactant alcohol is added, the rules of the spherical particles obtained good improvement. And when alcohol is added, SiO 2 and dispersion properties of the smoothness of the surface of the particles are very good. However, as R increases so that the system is close to the phase separation, the spherical morphology of the particles becomes irregular; when using the alcohol is n-octanol, as compared with the other two alcohols, an SiO , 2 rules of the worst of the spherical shape of the particles. Excluding alcohol is stirred in a higher R value or not for the Spherical an SiO 2 / sub> particles the size distribution of greater impact, vigorous stirring to favor the formation of single dispersion particle; lower and R stirring or not For a spherical SiO 2 particle size distribution of the impact is not significant. When the alcohol does not exist, without stirring, R 0.5 and ammonia concentration of 14.2% obtained when the fibrous of of SiO 2 ; does not exist alcohol, there is no agitation and specific R and ammonia concentration are fibers the necessary conditions for the formation of shaped particles. 4. Triton X-100 n-hexanol / cyclohexane / water system the CdS _AT_ SiO 2 control the synthesis of the core-shell structure and characterization using the inverse microemulsion Triton X-100 n-hexanol / cyclohexane / water system, using continuous sample generation of CdS nanocrystals and SiO 2 shell covering in a microreactor is completed, the systems of various reaction parameters of CdS @ SiO 2 core-shell nano-particles and CdS Nanocrystals nature. By increase in CdCl 2 with TAA (thioacetamide) volume than to 2:3 / 5, has been wrapped multiple CdS core-shell structure of the nano-products, known as \type structure. (Monodisperse particles is preferred, but the spherical shape is not very regular); determined by XRD experiments all CdS nanocrystals cubic structure, but calculated by the XRD patterns of CdS nanocrystals size is too small, indicating that this method to calculate the size of CdS Nanocrystals some error. Be wrapped nanocrystalline quantum size effects are reflected in the absorption and emission spectra; not wrapped in the average particle size of the nanocrystals with CdCl 2 , TAA, ammonia and TEOS volume ratio has nothing to do, no slightly larger than display quantum size effect; preparation of the core-shell structure resulting in an average particle size of CdS nanocrystals and not wrapped. The fluorescence spectra of the CdS nanocrystals through the wrapped compared to the strength and uncoated nanocrystalline increased slightly, but capture the emission intensity is significantly increased, indicating Nanocrystals increase in surface defects. Reaction time for the nature of the core-shell nanoparticles, was wrapped in nanocrystalline form of basic undifferentiated, TEM and XRD and UV absorption and fluorescence spectroscopy results are consistent. The particle size distribution of the reaction after 6h. The results of the fluorescence spectra show that the increase in reaction time helps to reduce surface defects of CdS nanocrystals. Small starting amount of water, the core-shell nano particle aggregation phenomenon is more severe with increasing initial water content, particle size and morphology changes. The starting CdS Nanocrystals increased water conducive crystalline. UV absorption by the wrapped and un-wrapped CdS nanocrystals show the quantum size effect, but the fluorescence spectrum just different luminous intensity. When CdCl 2 and TAA were 0.1mol / L and 0.01mol / L have been more interesting core-shell structure, in addition to multiple CdS nanocrystals are uniformly distributed in the SiO 2 the central portion, but also distributed over the surface of the core-shell nanoparticles. Interestingly, the average particle diameter of the wrapped parcel and without Nanocrystals undifferentiated. The fluorescence spectra showed that, a of SiO 2 shell covering an increase of the surface defects of the particles, and nano-crystalline two capture state exists. \the distribution of the central portion of the ball / sub> is attributed to the electrostatic interaction between the TEOS hydrolysis intermediates and CdS nanocrystals.

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