Nanoparticles synthesis approach

Figure 3. Schematic representation of the selective synthesis of metal nanowires and nanoparticles by the Sintering Controlled Synthesis approach, (a) Mesoporous silica, (b) impregnation of mesoporous silica with metal ions, (c) addition of water/alcohol vapors and UV-irradiation, or wet H2-reduction, (d) formation of metal nanowires, (e) dry H2-reduction, (f) formation of metal nanoparticles.

The approach described later on in this chapter builds upon a report in 2002, in which we proposed microfluidic reactors as favourable systems for nanoparticle synthesis, and showed that nanocrystalline cadmium sulfide prepared in such reactors exhibited improved monodispersity compared with particles prepared in conventional bulk-scale vessels (Edel et al., 2002). 

Currently, there is a growing need to develop environmentally benign nanoparticle synthesis processes that do not use toxic chemicals in the synthesis protocol. As a result, researchers in the held of nanoparticles synthesis and assembly have turned to biological systems for inspiration. The secrets gleaned from nature have led to the development of biomimetic approaches to the growth of advanced nanomaterials (Sastry et al., 2003). Besides this, the utilization of nontoxic chemicals. 

Mukherjee, P., Ahmad, A., Mandal, D., Sainkar, S.R., Khan, M.L, Parischa, R., Ajayakumar, P.V., Alam, M., Kumar, R., and Sastry, M. 2001a. Fungus mediated synthesis of silver nanoparticles and their immobilization in the mycelial matrix A novel biological approach to nanoparticle synthesis. Nano Letters, 1 515-9. 

Ferritin induced nanoparticle synthesis was adapted from a number of different synthetic strategies reliant upon the physical nature of ferritin. For instance, ferritin can readily exist in two stable forms (native ferritin with an intact iron oxide core or apo-ferritin lacking a mineral core) owing to the enhanced structural integrity of the protein shell. As a result, two general reaction schemes were adopted. The first route utilized the iron oxide core of native or reconstituted ferritin as a precursor to different mineral phases and types of iron nanoparticles, while the second invokes mineralization within the empty cavity of apo-ferritin. In the latter approach, the native protein must be demetallated by reductive dissolution with thioglycolic acid to yield apo-ferritin. Ultimately, apo-ferritin provides a widely applicable means to the synthesis of various nanoparticle compositions under many conditions. 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

Recent scientific literature demonstrates a growing interest in new methods of nanoparticle synthesis, driven primarily by an ever-increasing awareness of the unique properties and technological importance of nanostructured materials. The fabrication of nanoparticles within reverse microemulsions [40, 146] has been shown to be a convenient route to monodisperse particles of controllable size. A recognised goal of these synthetic approaches is to achieve control over the composition, size, surface species, solubility, stability, isolability and other functional properties of the nanostructures. The combination of reverse microemulsion and microwave heating has the added advantage that the oil phase in the reverse microemulsion system is transparent to microwave so that the aqueous domains are heated directly, selectively and rapidly. 

Thus, the first approach to CdS nanoparticle synthesis in both the outer and inner surfaces of the lipid vesicles seems to have been found. The main factors that control the sizes of the CdS nanoparticles in the inner cavities of the lipid vesicles were determined and some attempts to determine the nature of the rate-controlling step in the process of CdS particle growth in these cavities were also undertaken. 

Abstract Nanoparticles (NPs, diameter range of 1-100 nm) can have size-dependent physical and electronic properties that are useful in a variety of applications. Arranging them into hollow shells introduces the additional functionalities of encapsulation, storage, and controlled release that the constituent NPs do not have.This chapter examines recent developments in the synthesis routes and properties of hollow spheres formed out of NPs. Synthesis approaches reviewed here are recent developments in the electrostatics-based tandem assembly and interfacial stabilization routes to the formation of NP-shelled structures. Distinct from the well-established layer-by-layer (LBL) synthesis approach, the former route leads to NP/polymer composite hollow spheres that are potentially useful in medical therapy, catalysis, and encapsulation applications. The latter route is based on interfacial activity and stabilization by NPs with amphiphilic properties, to generate materials like colloidosomes, Pickering emulsions, and foams. The varied types of NP shells can have unique materials properties that are not found in the NP building blocks, or in polymer-based, surfactant-based, or LBL-assembled capsules. 

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