Nanoparticles using surfactant assemblies

By employing metal 2-ethylhexanoate precursors which act as photo-reactive surfactants, de Oliveira et al. have developed new routes to metal oxide nanoparticles. This surfactant assembles into a reverse micelle in organic solvent, in effect forming a nanoreactor which promotes metal oxide nanoparticle formation within the micelle. The authors have demonstrated the synthesis of C03O4 and Bi metal nanoparticles using this route, but it is likely this clean approach could be employed to prepare a range of nanoparticles with a choice of surfactants. 

Surfactants provide several types of well-organized self-assembhes, which can be used to control the physical parameters of synthesized nanoparticles, such as size, geometry and stability within liquid media. Estabhshed surfactant assembles that are commonly employed for nanoparticie fabrication are aqueous micelles, reversed micelles, microemulsions, vesicles [15,16], polymerized vesicles, monolayers, deposited organized multilayers (Langmuir-Blodgett (LB) films) [17,18] and bilayer Upid membranes [19](Fig. 2). 

Some miscellaneous examples of QD synthesis using surfactant systems are described below. A layer-by-layer [206] structure of dithiol self-assembled monolayers (SAM) and CdS mono- and multilayer nanoparticles were fabricated on a gold substrate covered with alkanedithiol. SAMs were formed by an alternate immersion of the substrate into ethanolic solutions of dithiol, and dispersion of CdS nanoparticles (ca. 3nm in diameter), the latter of which was prepared in A0T/H20/heptane w/o microemulsions. 

To arrange NC or nanoparticles into an assembly is inevitable in order to utilize them for practical purposes. An assemblage in a finely regulated manner is always desired. It is therefore developed to control the interparticle separation. One of the most interesting methods, very rational but not too complicated, is the use of the thermal change in the state of surfactants adsorbed on the surface of nanoparticles. Kotov et al. (30) showed that the interparticle separation of titania NC of 2.0 0.5 nm could be controlled from 0.9 nm to 0.2 nm depending on the heat treatment condition, from 90 min at 70°C to 120 min at 90°C. 

Nanoparticle shape control can be easily effected by using self-assembled structures such as micelles (arising due to spontaneous assembly of suitable surfactants in water) as templates [4-6]. 

Improvement in the photocatalytic activity of these materials has been achieved in recent years by different methods including sensitization of the catalyst using dye molecules and doping the catalyst with norrmetals such as nitrogen, carbon, fluoride and iodide, and transition metals (Au, Pt, Ag, and Pd). Hahnemann and Ismail [110] have recently reviewed the recent developments in the syntheses of mesoporous TiOj as active photocatalysts by the surfactant assembly as well as the preparation and characterization of doped mesoporous Ti02 networks with transition metals ions, noble metals, and nonmetal species. Mesoporous titania nanoparticles will play an important role in the environmental protection and the search for renewable and clean technologies. 

The preparation of nanomaterials is one of the most active fields in material science. Number of techniques have been used for the production of nanoparticles gas-evaporation [11], sputtering [12], sol-gel method [13], hydrothermal [14], microemulsion [15, 16], polyols [17], laser pyrolysis [18], sonochemical synthesis [19], chemical coprecipitation [20-22], and so on. Among them, the surfactant assembly mediated synthesis is attracting more attention because it allows for a good... 

Mesoporous oxides have been fabricated using a variety of methods spanning templated self-assembly of nanoparticles, nanocasting and using surfactants to act as a molecular scaffold to help build the mesoporous architecture. Template-free self-assembly of nanoparticles via ice crystallisation has also been achieved, where the phase change from water to ice sculpts the nanoparticles into... 

Conventional SERS substrates typically have disordered nanoscale features, such as that found in electrochemically roughened Au or Ag surfaces.170 SERS substrates can also be rationally designed by lithography, by self-assembly, or a combination of the two. Both supramolecular and nanoscale self-assembly methods can be used to fabricate two-dimensional Au nanoparticle arrays with tunable optical properties.33 171172 For example, macrocyclic surfactants based on resorcinarenes (a subclass... 

One of the first examples of mesoscopic-macroscopic two-dimensional ordering within a structure involved a bacterial superstructure formed from the co-aligned multicellular filaments of Bacillus subtilis that was used to template macroporous fibers of either amorphous or ordered mesoporous silica [82], The interfilament space was mineralized with mesoporous silica and, following removal of the organic, a macroporous framework with 0.5 pm wide channels remained. Mesoporous silica channel walls in this hierarchical structure were curved and approximately 100 nm in thickness. Dense, amorphous walls were obtained by replacing the surfactant-silicate synthesis mixture with a silica sol solution. The difference in the mode of formation between porous and non-porous wall structures was explained in terms of assembly from close-packed mesoporous silica coated bacterial filaments in the former compared to consolidation of silica nanoparticles within interfilament voids in the latter. 

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