Nanoparticles of metals

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

Veranth JM, Kaser EG, Veranth MM, Koch M, Yost GS (2007) Cytokine responses of human lung cells (BEAS-2B) treated with micron-sized and nanoparticles of metal oxides compared to soil dusts. Part Fibre Toxicol 4(1) 2. 

FIGURE 1.2. Formation of nanoparticles of metal oxide by reverse micelle method. A solution of inverse micelles is first formed by adding a long-chain alkylamine to a toluene solution. A small amount of water is trapped in the reverse micelle core. Mixing the reverse micelle solution with an aluminum alkoxy amine adduct results in hydrolysis of the aluminum alkoxide adduct and formation of nano-sized particles of aluminum oxyhydroxide after drying. These particles are shown in the SEM picture above. 

The size of fine particles, especially nanoparticles, of metal can be measured only by transmission electron microscopy (TEM). Usually a microscope with the magnitude larger than 100,000 is used for the measurement. The sizes of more then 200 individual particles should be measured. The results are shown as histograms, from which the average diameter and standard deviation can be calculated. If the relative standard deviation is less than 10%, the particles can be said to be well monodispersed. 

Nanoparticles of metals such as Au, Ag, Pd and Pt embedded in exfoliated sheets of aminociays of the type R8Si8Mgs0lfi-(OH)4, where R = CH2CH2NH2 are entirely water soluble. These sheets of the composite come to the organic-aqueous interface on addition of alkane thiols to the aqueous layer. 

Microemulsions are used as reaction media for a variety of chemical reactions. The aqueous droplets of water-in-oil micro emulsions can be regarded as minireactors for the preparation of nanoparticles of metals and metal salts and particles of the same size as the starting microemulsion droplets can be obtained [1-3]. Polymerisation in micro emulsions is an efficient way to prepare nanolatexes and also to make polymers of very high molecular weight. Both discontinuous and bicontinuous micro emulsions have been used for the purpose [4]. Microemulsions are also of interest as media for enzymatic reactions. Much work has been done with lipase-catalysed reactions and water-in-oil microemulsions have been found suitable for ester synthesis and hydrolysis, as well as for transesterification [5,6]. 

Most of our discussion thus far has involved some rather extreme synthetic environments of laser, arc, or pyrolysis. However, a preferred route toward nano-clusters/nanoparticles of metals and their compounds is through use of relatively mild conditions - often taking place at room temperature on the benchtop. This is not possible for carbon nanoallotropes, since the precursor e.g., graphite) contains... 

Photoreactions on titanium dioxide have been the focus of considerable interest for some time. Titania offers the opportunity to oxidize organic compounds in polluted environments, and has also been exploited to generate titania-supported nanoparticles of metals (e.g., silver) via photoreduction reactions [85]. While there is not enough room here to thoroughly treat photocatalytic processes, a brief introduction to the subject is presented below. Readers seeking detailed treatments of this subject are referred to a recent review by Yates etal. on titania-facilitated photocatalysis [86]. 

Walter EC, Murray BJ, Favier F, Penner RM (2003) Beaded bimetallic nanowires wiring nanoparticles of metal 1 using nanowires of metal 2. Adv Mater 15 396-399... 

Recently, Chen et al. [54] have synthesised nanoparticles of metallic Cu and also CU2O by radiolytic reduction of Cu2+in microemulsion medium where non-ionic surfactants, e.g. Brij30, Brij56 or Triton X100 with different co values were used. Anions and surfactants had remarkable effect on the radiolytic reduction process. They also affected the morphologies of the reduction products. Thus, in the presence of toluene with Brij56 microemulsion the radiolytic reduction product was metallic copper but replacement of toluene... 

Pulsed laser ablation of metal samples in liquid environments by combination (in coincidence or in sequence) of two laser beams at different wavelengths has been examined in order to clarify a possibility of formation of size-selected metal nanoparticles. It has been shown that dual laser ablation technique in transparent liquids is suitable for fabrication of nanoparticles of metals where the size of particles can be controlled. The mean diameter of silver particles fabricated in water was typically in the range of 15-20 nm. 

A major new sub-field of cluster chemistry is that of nanoparticles of metals in which there are no intentionally appended ligands. These are not molecular and thus neither homodisperse nor crystalline. 

The addition of superacid metal (IV) phosphonates is particularly suitable for the preparation of hybrid membranes. The proton conductivity in some cases reaches values even higher than 0.1S cm. The presence of nanoparticles of metal phosphonates in the electrode interface Nalion/Pt already improves the electrochemical characteristics of fuel cells in the temperature range 80-130°C [36]. 

Most often, the reaction with the nanoparticles of metal is performed without solvent but some experiments were made with Sn(n-C4H9)4 in heptane. Whatever the method and the metal, the reaction can be decomposed into several steps, quite similar to those reported for the reaction of organometallics with the surfaces of oxides [78] ... 

A. I. Kryukov, N. N. Zinchuk, A. V. Koizhak, S. Ya. Kuchmiy An Influence of the Conditions of Catalytic Synthesis of Nanoparticles of Metallic Silver on Their Plasmon Resonance, Theoret iExperim. Khimiya. 2003, v. 39,N 1,8-13 (inRussian). 

On the other hand in the case of nanoparticles of metals, their oxides, etc., the macromolecules provide both ligand protection and stabilization of the nanosized particles. Different techniques such as microencapsulation, mech-anochemical dispersion or formation/structural organization of nanoparticles in macromolecules are used for preparing such systems. The catalytic activities of these materials, in which the nanoparticles form the active part, are particularly studied. 

Nanoparticles of metals may be co-dispersed with a polymer matrix in different ways in high-speed planetary mills, disk integrators or vibrators of various types including ultrasonic. Magnetodynamic dispersers are used for the dispersion of magnetic particles in polymers (specifically, y-Fe203). 

Whereas the appropriate forms of zeolites and related solids are widely used in acid-catalysed industrial processes, microporous solids are not currently of importance in commercial base-catalysed conversions. Instead, high-surface-area forms of alkali metal and alkaline earth metal oxides and hydroxides, often supported on alumina, fulfil the need for solid base catalysts. Nevertheless, interest remains in characterising basic sites in cationic zeolites and in developing routes to more strongly basic sites in microporous solids." Routes to the latter include the introduction of metallic forms of alkali metals or nanoparticles of metal oxides and the partial replacement of amine groups at the sites of framework oxygen atoms. Porous solid bases have been shown to exhibit a varied catalytic chemistry, particularly for reactions such as dehydrogenations,... 

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