Monodisperse nanoparticles

Fig. 1.4 Size and shape control of Pt coUoid nanoparticles. Monodispersed platinum nanoparticles 1.7 and 7.2 nm in size (left) with weU-controUed cubic or cuboctahedral shapes (right). Scale bar (left) 5 nm, (center) 50 nm, and (right) 5 nm. The % values (right) refer to the % of nanoparticles with the corresponding shape. (Adapted from ref [28], reprinted with permission)...

Figure C2.17.3. Close-packed array of sub-micrometre silica nanoparticles. Wlren nanoparticles are very monodisperse, they will spontaneously arrange into hexagonal close-packed stmcture. This scanning electron micrograph shows an example of this for very monodisperse silica nanoparticles of -250 nm diameter, prepared in a thin-film fonnat following the teclmiques outlined in [236].

In the transmission electron microscopy (TEM) images, the starch nanoplatelets (SNPs) are believed to aggregate as a result of hydrogen bond interactions due to the surface hydroxyl groups [13] (Fig. lA). Blocking these interactions by relatively large molecular weight molecules obviously improves the individualization of the nanoparticles. The acetylated starch and cellulose nanoparticles (SAcNPs and CelAcNPs) appeared more individualized and monodispersed than their unmodified counterparts with a size of about 50 nm (Fig. IB C). 

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. 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

Oluwafemi, O. S. and Revaprasadu, N. (2009). A Facile, Green" One - Step, Room Temperature Synthesis of a Series of monodispersed MSe(M = Cd or Zn)Water Dispersible Nanoparticles. Mater. Res. Soc. Symp. Proc., 1138, FF 12-19. 

Moreover, stable liquid systems made up of nanoparticles coated with a surfactant monolayer and dispersed in an apolar medium could be employed to catalyze reactions involving both apolar substrates (solubilized in the bulk solvent) and polar and amphiphilic substrates (preferentially encapsulated within the reversed micelles or located at the surfactant palisade layer) or could be used as antiwear additives for lubricants. For example, monodisperse nickel boride catalysts were prepared in water/CTAB/hexanol microemulsions and used directly as the catalysts of styrene hydrogenation [215]. 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

The synthesis of nanoparticles has been intensively pursued not only for their fundamental scientific interest, but also for many technological applications [1]. For many of these applications, the synthesis of monodisperse nanoparticles (standard deviations a < 5%) with controlled particle sizes is of key importance, because the electrical, optical, and... 

The primary goal of the researchers has been to produce Q-dots possessing all of the attributes of the Q-dots prepared using liquid-phase synthetic methods (that is adjustability of the nanocrystal identity and diameter and size monodispersity) and also the technological utility of Q-dots prepared by MBE (specifically, the deposition of nanocrystals with a defined orientation and an electrical output contact). It was shown that the E/C-synthesized 5-CuI and CdS Q-dots were indeed epitaxial with narrow size distribution and strong photoluminescence tunable by the particle size. Qne of the advantages of the E/C method is that it can be made size selective. The key point is that the size as well as the size dispersion of product nanoparticles are directed actually by the corresponding properties of the metal nanoparticles therefore the first deposition step assumes special importance. 

In order to make practical use of the physical properties of nanoparticles, whether individual or collective, one has to find a way to address them. If we leave out the near field techniques, this in turn requires that the particles be monodisperse and organized in two or three dimensions. It is therefore necessary to imagine techniques allowing the self-organization and even, ideally, the crystallization of nanoparticles into super-lattices. 

In summary, control of the surface chemistry and the presence of clean surfaces allow the coalescence of initially isotropic nanoparticles into regular, often monodisperse, nano-objects of anisotropic shape (cubes, rods, wires). It is possible that the inclusion of the initially present nanoparticles into superlattices play an important role in these coalescence processes. 

The efficient hydrogenation of various benzene compounds in biphasic systems has also been described by similar surfactant-protected irid-ium(O) nanoparticles [47]. The solubility of the nanoparticles was assured by 10 equivalents of water-soluble N,N-dimethyl-N-cetyl-Ar-(2-hydroxyethyl)-ammonium chloride salt. TEM observations show that the particles are monodispersed in size with an average diameter of 1.9 0.7 nm (Fig. 7). 

Electric-field-directed growth of gold nanorods in aqueous surfactant solutions. Advanced Functional Materials, 14, 571-579 (d) Jana, N.R. (2005) Gram-scale synthesis of soluble, near-monodisperse gold nanorods and other anisotropic nanoparticles. Small,... 

An interesting 3D superlattice of the main group metal tin has recently been generated [36]. When Sn(NMe2)2 is treated with hexadecylamine and HCl, perfect 3D superstructures of monodisperse 18 x 15nm Sn nanoparticles could be characterized. 

From the viewpoint of size control, bimetallic systems are usually very convenient to produce monodispersed metal nanoparticles [49]. Although the exact reason is not clear yet, this is probably attributed to the redox equilibrium between the two elements. 

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