Microemulsion synthesis

Zarur AJ, Ying JY (2000) Reverse microemulsion synthesis of nanostructured complex oxides for catalytic combustion. Nature 403 65-67... 

Darbandi, M., and Nann, T. (2005) Single quantum dots in silica spheres by microemulsion synthesis. 

MICROEMULSION SYNTHESIS AND MAGNETIC PROPERTIES OF Co Pt CORE-SHELL NANOPARTICLES... 

Tilley RD, Yamamoto K. The microemulsion synthesis of hydrophobic and hydrophilic silicon nanocrystals. Adv. Mat. 2006 18 2053-2056. 

The potential capabilities of microemulsion synthesis of colloidal silica and related materials are yet to be realized. For example, the compartmen-talization of reagents at the molecular level in these media may allow close control of chemical homogeneity in the synthesis of glass (e.g., Si-Al) particles. In situ synthesis of silica-supported catalysts and synthesis protocols involving seeding techniques, coating techniques, or infiltration are also possible. 

During the last few years, different synthetic procedures have been reported for the synthesis of magnetic nanoparticles. These methods include co-precipitation, thermal decomposition and/or reduction, microemulsion synthesis, and hydrothermal synthesis. Despite poor shape control and quite polydisperse particles, co-precipitation is probably the simplest synthetic route. By contrast, thermal decomposition is experimentally more demanding but affords the best results in... 

As a solution-based materials synthesis technique, the microemulsion-mediated method [10-18] offers the unique ability to effect particle synthesis and particle stabilization in one step. The solubilized water droplets serve as nanosize test tubes, thus limiting particle growth, while the associated surfactant films adsorb on the growing particles, thereby minimizing particle aggregation. The purpose of this chapter is to review the literature on the microemulsion-mediated synthesis of metal hydroxides and oxides the definition of a metal is extended here to include the semimetal silicon. Since metal oxides are frequently produced by decomposing metal salts, aspects of the literature on microemulsion-derived metal salts are also considered. In principle, any previously established aqueous precipitation chemistry can be adapted to the microemulsion synthesis technique. Accordingly,... 

Only one study was found on microemulsion-based preparation of zinc oxide [103]. The two-microemulsion synthesis protocol was used by Hingorani et al. [103] to prepare zinc carbonate that was then calcined ( 220 C) to produce zinc oxide. Working with the CTAB/butanol/octane/water microemulsion system and the two-microemulsion protocol, one aqueous pseudophase contained zinc nitrate while the other contained ammonium carbonate. X-ray diffraction identified the resulting calcined particles as ZnO with an average particle size of 14 nm. 

Fig. 5.9 Technological flowsheet for microemulsion synthesis of the ferroelectric nanoparticles...

Fig. 5.10 Barium titanate particle size distribution originating from microemulsion synthesis (a) and HRTEM image of single particle (b)...

Table 5.7 Characteristics of nanoferroics obtained by micellar/microemulsion synthesis [117]...

Table 2.2 Some surfactants used in macro- and microemulsion synthesis of particles.

On heating the dried precursor up to 600 C/3h, well-crystallized y-Fe203 was obtained as an intermediate. At 650"C, the first signs of the ferrite were observed. Pure phase SrFei20i9 was obtained at 900 C/3h. The particle size (78 nm after calcination at 900"C) was much larger than expected in microemulsion synthesis. 

A W/O microemulsion synthesis of Fe203, Ni, sZn5Fe204 and Mn, 5ZngFe204 particles was recently reported by Yener and Giesche [314]. The synthesis was carried out by the two-microemulsion technique using AOT/isooctane/aqueous phase, where the aqueous phase was either... 

A reverse microemulsion synthesis of CaCOa was reported later by Roman et al [339] who used xylene, a diluent oil (100-150 NS grade), 70% active sulfonic acid, calcium hydroxide and methanol the water content was evidently very small. Carbon dioxide was bubbled through the system the conversion was almost total within 0.5h. Water and methanol were separated by distillation. The particle size of the carbonates was around 1.5-3.0 nm. 

Rees et al. [342] provide an elaborate description of two-microemulsion synthesis of CaS04 which clearly indicates a dependence of the particle morphology on the w value and concentrations of the other constituents. As an example, in the system Ci2E4/cyclohexane/aqueous Ca-nitrate or Na-sulfate, a progressive change in the value of w from 2 to 20 changed the particle morphology from nanospheres to nanorods via nanowires. 

An additional experimental feature in two-microemulsion synthesis of CdS clusters, reported by Liu etal. [224], was hydrothermal treatment. The continuous phase was petroleum ether, the surfactant a mixture of NP-5 and NP-9 (weight ratio 2 1), and the water phases in the two microemulsions were aqueous solutions of cadmium chloride and thioacetamide (both of O.IM concentration). The two microemulsions were mixed in equal amounts under stirring at room temperature. The mixture was charged into a teflon-lined autoclave for hydrothermal treatment at 30° and 120°C. The produced clusters had average size of 20 nm (30°C) and 80 nm (120°C) the crystals were a-CdS (Greenockite type). 

Brij 30 or ammonium laurate in hexane constituted the reverse micelle used by Bonini etal. [230] for two-(reverse)microemulsion synthesis of gold particles. The microemulsions contained HAUCI4.3H2O or hydrazine hydroxide in the aqueous phase. The w value was the same ( l-5) in both the cases, but the concentrations of the aqueous phases were different [hydrazine] = I0[gold]. 

The importance of polydispersity - or its control - in microemulsion-mediated synthesis of particles has been mentioned early in this Chapter. Indeed, Pileni [100] has indicated that for future optical (e.g. non-linear) devices, a control on the formation of monodisperse nanoclusters will prove to be important. Similar observations have been made by various other workers [e.g. 242]. It is therefore justified, before we end this discussion on microemulsion synthesis of nanoparticles, to look at the observations of some of the workers in this area and see if some commonalities can be observed for general application. 

While effective removal of surfactant molecules from freshly precipitated nanoparticles constitutes one of the involved issues in microemulsion synthesis, a coating of surfactants on nanoparticles has been found to improve their luminescence behavior in certain cases. Thus, Fei etaL [284] synthesized a-Fe203 particles from reverse microemulsions in which sodium dodecyl benze sulfonate (DBS) was the selected surfactant. The a-Fe203 organosols with the particles coated by DBS and heat-treated at 140 C showed strong visible luminescence while the uncoated particles prepared under similar conditions were not luminescent. 

X. Zhang and K. Y. Chan, Microemulsion synthesis and electrocatalytic properties of platinum-... 

Fig. 6.5 Example of microemulsion synthesis chemical reduction of metal precursors aiming at preparing metal nanoparticles (Reproduced from Ref. [71] with the permission of hiTech)...

Zhang X, Chan KY. Water-in-oil microemulsion synthesis of platinum ruthenium nanoparticles, their characterization and electrocatalytic properties. Chem Mater 2003 15 451-9. 

In recent decades, there have been many attempts to fabricate CNT/PANI composites [329-337]. The incorporation of nanotubes into PANI can result in novel composite materials with enhanced electrical, electrochemical, and mechanical properties. Eor example, Yu et al. prepared MWCNT/PANI nanocomposites through in situ inverse microemulsion synthesis [334]. Such nanocomposites are characterized by very strong interaction between MWCNTs and conducting polymers. Moreover, MWCNT/PANI core-shell nanowires exhibited better thermal stability and electrical conductivity than the pure PANI. The electrical conductivity of MWCNT/PANI composite containing 1 wt% of MWCNTs increased by one order of magnitude (pure PANI 0.02Scm MWCNT/PANI composite 0.20Scm-i) [334]. 

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