Particles in reversed micelles

A higher level of size and morphology control in the incipient semiconductors has been accomplished in reversed micelles prepared from cadmium AOT [614] and from mixtures of cadmium AOT and sodium AOT [615] or, alternatively, by arresting particle growth by surface derivatization [592, 621, 622]. Indeed, surface derivatization of semiconductor clusters was first reported for particles in reversed micelles [621] the reversed micelles act to confine precursor ions and to control the growth of the semiconductor particles. Conditions are typically arranged so that, initially, there is no more than one metal ion (say Cd2+) per water pool. Addition of a heptane solution of bis(trimethylsilyl) selenium resulted in the formation of size-quantized metal selenide particles (say CdSe) in the reversed micelles. This solution could be evaporated to dryness and the resultant particles could be reconstituted in a hydrocarbon solvent Alternatively, addition of metal (say Cd2+) ions to the reversed-micelle-entrapped metal selenide particles, followed by the addition of alkyl(trimethylsilyl)selenium, RMSiMe3, led to the formation of alkyl-capped... 

Hirai T., Sato H., Komasawa I. Mechanism of formation of titanium dioxide ultrafine particles in reverse micelles by hydrolysis of titanium tetrabutoxide. Ind. Eng. Chem. Res. 1993 32 3014-... 

Pileni MP, Lisiecki I (1993) Nanometer metallic copper particle synthesis in reverse micelles. Colloids Surf A 80 63-68... 

It is important to note that in addition to microporous solids, other chemical systems have been used to template the growth of nanomaterials. For example, emulsions have been used to pattern both the pores in titania [14] and the packing of latex particles [46]. Reversed micelles have also been used as patterning agents. Examples include the syntheses of super-paramagnetic ferrite nanoparticles [15] and BaC03 nanowires [47]. Finally, carbon nanotubules have also been used as templates [16,48,49]. A variety of nanomaterials including metal oxides [16,48,49] and GaN have been synthesized inside such tubules [50]. 

Sato H, Ohtsu T, Komasawa 1 (2000) Atomic force microscopy study of ultrafine particles prepared in reverse micelles. J Colloid Interface Sci 230 200-204... 

Hirai T, Bando Y, Komasawa I (2002) Immobilization of CdS nanoparticles formed in reverse micelles onto alumina particles and their photocatalytic properties. J Phys Chem B 106 8967-8970... 

In principle, silica growth kinetics may be controlled by (1) slow release of monomer via alkoxide hydrolysis in the particle-free reverse micelles, (2) slow surface reaction of monomer addition to the growing particle, and (3) slow transport processes as determined by the dynamics of intermicellar mass transfer. There is strong experimental evidence to support the view that the rate of silica growth in the microemulsion environment is controlled by the rate of hydrolysis of TEOS (23,24,29). Silica growth kinetics can be analyzed in terms of the overall hydrolysis and condensation reactions ... 

A OT/Cd(NO )2Hsooctanel Water Reverse Micelles in the Presence and the Absence of HMP. In the presence of an excess of cadmium ions, [Cd2+]/[S2 l = 2, the absoiption spectra obtained at various water content, w, in Na( AOT) reverse micelles in the presence and in the absence of HMP show a red shift with increasing the water content, w. For a given w value, a blue shift in the presence compared to the absence of HMP is observed. As described in the litterature (28,34,37), the average size of the particles can be deduced from the absorption onset. The size of the semiconductor is always less than that obtained in aqueous solution. The presence in reverse micelles of HMP as a protecting agent allows a reduction in the size of the particle. 

The addition of macrocycles on CdS synthesis in reverse micelles induces a strong change in absorption spectra. For a given water content, a red shift of absorption onset is observed in presence of macrocycles. This effect is more pronounced in presence of Kryptofix 222 and when the CdS nanocrystallite synthesis is realized in presence of an excess of sulfide S2 ions (x = ). This red shift is characteristic of an increase in the average nanocrystallite size. It can be noticed that absorption of CdS particles synthetized in reverse micelles in presence of an excess of cadmium Cd2+ ions (x = 2) is reduced in presence of macrocycles. This indicates a decrease in the yield of CdS particles and is attributed to complexation of functionalized... 

The analogous capping of cadmium selenide particles by organo(silyl)-selenides in reversed micelles will be discussed in Sect. 4.4. 

AOT-isooctane-H20 reversed micelles 50-A-diameter CdS particles generated in situ in reversed micelles from CdCl2 or Cd(N03)2 by H2S Reversed-micelle-entrapped CdS was fluorescence quenched by methylviologen band-gap excitation in the presence of Rh as catalyst and PhSH as sacrificial electron donor resulted in water photoreduction 611... 

A0T-heptane-H20 reversed micelles Small (10 A diameter) CdS particles prepared in situ in reversed micelles from Cd(C104)2 and Na2S Agglomeration number grew discontinuously CdS was fluorescence quenched by MV2+ 612... 

AOT-isooctane-H20 reversed micelles Monodispersed CdS particles generated in situ in reversed micelles Size of CdS depended on the ratio of Cd2+ to S2 strong fluorescence was observed in the presence of excess Cd2+ high yield of CdS-mediated MV2+ photoreduction 612... 

Cadmium lauryl sulfate-, Cd(LS)2, and cadmium dioctylsulfosuccinate-, Cd(AOT)2, isooctane-H20 reversed micelles Size-quantized CdS particles generated in situ in reversed micelles Immobilized Cd(LS)2 or Cd(AOT)2 controlled the sizes of incipient CdS 614... 

NaA0T-n-heptane-H20 reversed micelles Size-quantized CdS particles generated in situ in reversed micelles... 

NaA0T-n-heptane-H20 reversed micelles Single-compartment, 800-to 1000-A-diameter dihexadecylphosphate (DHP) surfactant vesicles Single-compartment dioctadecyldimethylammonium chloride (DODAC) (6) vesicles Thiophenolate-ion-capped, size-quantized CdS generated in situ in reversed micelles CdS particles prepared in situ in vesicles from Cd2+ by controlled exposure to h2s CdS particles generated in situ in DODAC vesicles by several methods... 

Colloidal semiconductor particles were in situ generated and coated by catalysts in reversed micelles, surfactant vesicles and polymerized surfactant vesicles. 

Figure 4. Schematic description of the preparation of capped CdSe particles by arrested precipitation in reverse micelles,...

Particles of the enzymatically synthesized phenolic polymers were also formed by reverse micellar polymerization. A thiol-containing polymer was synthesized by peroxidase-catalyzed copolymerization of p-hydroxythiophenol and p-ethylphenol in reverse micelles [70], CdS nanoparticles were attached to the copolymer to give polymer-CdS nanocomposites. The reverse micellar system was also effective for the enzymatic synthesis of poly(2-naphthol) consisting of qui-nonoid structure [71], which showed a fluorescence characteristic of the naphthol chromophore. Amphiphilic higher alkyl ester derivatives were enzymatically polymerized in a micellar solution to give surface-active polymers at the air-water interface [72, 73]. 

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