Stable nanoparticles, synthesis

It must be pointed out that formation and stabihzation of nanoparticles in reversed micelles are the result of a delicate equilibrium among many factors. In addition, lacking a general theory enabling the selection a priori of the optimal conditions for the synthesis of nanoparticles of a given material with the wanted properties, stable nanoparticles containing w/o microemulsions can be achieved only in some system-specific and experimentally selected conditions. 

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. 

In summary, in this Section we have described how electronic and geometric effects may contribute to facilitate the ORR reaction on a bimetallic alloy. The next question is, what elements are on the surface of a bimetallic alloy, and even more complex, what is on the surface of a nanoalloy Obviously this question is closely dependent on the nanoparticle synthesis, but it also relates to the thermodynamic and kinetic conditions that make an alloy particle of a given size and shape to be stable or to adopt other configurations such as core-shell stractures, which is the topic of the next Section. 

One of the main problems in modern nanotechnology is the preparation and stabilization of nanoparticles of different nature semiconductors, metals, organic compounds, etc. Nowadays there are a number of methods for nanoparticle synthesis [1]. Among them water-in-oil reverse micelles (RMs) are the successful technique for the controlled preparation of very small and monosized nanoparticles. Water-in-oil RMs are thermodynamically stable dispersion of nanosized water drops in organic solvent, stabilized by surfactants. RMs are formed spontaneously due to the surfactants, which diminish the interface tension down to ultralow values, and as a result the free energy decreases when the total oil-water interfacial area increases. Thermodynamically stable water-in-oil microemulsions can be produced at strictly defined conditions. It is possible to change the size of the water pool of RMs by variation of the ratio between water and surfactant concentrations. This allows changing the size of nanoparticles, which are stabilized in such microemulsions. 

Several approaches have recently been developed that directly apply natural architectures for artificial chanical reactions, some of which are detailed in different chapters of this book. Although not classified as homogeneous catalysis, the reduction of metal salts inside nanoreactors could be the first step on the way to reactivity with the corresponding metal coUoids or nanoparticles in e.g. hydrogenation reactions. A variety of carrier systems have been studied lately, including virus capsids, polymeric micelles, miniemulsions and hollow core-shell particles, as nanoreactors and hosts for the synthesis and encapsnlation of well-defined, stable nanoparticles. ... 

A successful SERS application to microfiuidic biosensors requires several key steps, including an instrumental setup of the Raman microscope, a special design for the microfiuidic channel, a synthesis of stable nanoparticles and antibody conjugations, and an optimal flow rate control. The overview of the SERS detection techniques can be simply denoted as follows (Fig. 1). 

Aerosol nanoparticle synthesis of various chemistries 6.3.1.1.3.1 Generation of stable S1O2 aerosol nanoparticles... 

ATRP in inverse miniemulsion [149] and microemulsion [150] polymerizations has been applied to the prodnction of water-soluble POEOMA homopolymer and copolymers. The first successfnl ATRP in inverse miniemulsion described the synthesis of stable nanoparticles of well-controlled water-soluble POEOMA... 

CuNPs) in Fig. 7 shows the monodisperse and uniformly distributed spherical particles of 10+5 nm diameter. The solution containing nanoparticles of silver was found to be transparent and stable for 6 months with no significant change in the surface plasmon and average particle size. However, in the absence of starch, the nanoparticles formed were observed to be immediately aggregated into black precipitate. The hydroxyl groups of the starch polymer act as passivation contacts for the stabilization of the metallic nanoparticles in the aqueous solution. The method can be extended for synthesis of various other metallic and bimetallic particles as well. 

Malik, M. A. Revaprasadu, N. and O Brien, P. (2001). Air-stable single-source precursors for the synthesis of chalcoeenide semiconductor nanoparticles. Chem. Mater., 13, 913-920. 

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