Nanoclusters stability

This chapter will mainly deal with the advantages of the alkaline EG synthesis method for the chemical preparation of noble metal nanoclusters stabilized by EG and simple ions, as well as the excellent performances of the functional materials assembled using these unprotected metal nanoclusters as building blocks. 

Scheme 1. Procedure of alkaline EG method for the chemical preparation of metal nanoclusters stabilized by EG and sample ions.

Synthesis of Metal Nanoclusters Stabilized by Ethylene Glycol and Simple Ions... 

Figure 1. TEM images and size distributions of Pt, Rh and Ru nanoclusters stabilized by EG and simple ions [11] (a) Pt nanoclusters (0.37g/1) (b) Pt nanoclusters (3.7g/1) (c) Rh nanoclusters (0.31 g/1) (d) Ru nanoclusters (0.32g/1). (Reprinted from Ref [11], 2000, with permission from American Chemical Society.)...

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

Figure 2. TEM micrographs of metal nanoclusters stabilized by microgel M5 from left to right Pd (reduced with NaHBEts), Pd (reduced with EtOH), Pt (reduced with NaHBEts).

In this section, a description of the experimental procedure used to prepare and characterize metal nanoclusters stabilized by DMAA-based microgels (M5, MIO, M20) is provided. Details of the experimental procedure used to prepare nanoparticles stabilized by MMA-based microgels have been reported elsewhere [13b]. 

Further insight into histidine encapsulation of nanoclusters (Au, Ag, Cu, Pt) was provided by infrared spectroscopy. IR spectra of free histidine showed a set of stretching bands for the N-H bond of the amine and strong peaks (1630 cm, 1413 cm ) attributed to an asymmetrical and symmetrical C02 stretch. As a result of nanocluster stabilization and the subsequent formation of a metal-N(His) interface, the N-H stretching frequencies broadened and the number of bands decreased relative to free histidine due to the interactions with the dielectric field at the nanocluster surface. ... 

Ott LS, Finke RG (2007) Transition-metal nanocluster stabilization for catalysis a critical review of ranking methods and putative stabilizers. Coord Chem Rev 251 1075 Yang J, Lee JY, Too H-P (2006) Size effect in thiol and amine binding to small Pt nanoparticles. Anal Chim Acta 571 206... 

Figure 3 Radiation-induced metal clusters, (a) Silver nanoclusters stabilized by PVA (10 nm). (b) STM imaging ofa single duster of the blue sol of silver oligomers Agd formed by y irradiation (n = 4). (c) Clusters ofAg, partially reduced by irradiation and then chemically developed by EDTA. (100 nm large and 15 nm thick), (d) TEM bright-held Image ofNi , PVA clusters (5 nm). (e) Two-dimensional self-assembled array of gold dusters (PVA) on mica with remarkable homodisperse size (5 nm). (f) Monocrystalline Pt nanotubes with CPCI (10 nm diameter and a few 100 nm long), (g) Pt nanorods with CTAB (3-4 nm thick and 20-40 nm long).

A rather effective catalyst proved to be the system of rhodium nanoclusters stabilized with pol5winylpirrolidone (PVP) and supported on finely dispersed oxides (gamma-alumina, silica, or titania) and modified with Cnd (Huang et al. ). With this system EtPy was hydrogenated at 25 C and 70 bar hydrogen in THE with a TOP of 58.6 min and an ee of 65.4%. 

Realistic models must account the stmeture of surface, shape and dimension of nanoclusters, as well as their chemical composition, which sufficiently change both their catalytic activity and corrosive resistance. It should be noted, that there are no theories of nanocluster stability improvements, developed up to date. 

FIGURE 15.3 The dependence of nanoclusters stability measure Aj on testing temperature T for PC(1) and PAR(2). The vertical shaded lines indicate temperature for PC (1 ) and... 

Therefore, the stated above results showed synergetics principles applicability for the description of association (dissociation) processes of polymer segments in local order domains (nanoclusters) in case of amorphous glassy polymers. Such conclusion can be a priori, since a nanoclusters are dissipative structures [6], Testing temperature increase rises nanoclusters stability measure at the expense of possible reformations number reduction [14, 15],... 

Another example of metal(O) nanoparticles catalysts for the dehydrogenation of DMAB has been reported very recently, describing the preparation and characterization of ruthe-nium(O) nanoclusters stabilized by 3-aminopropyltriethoxysilane [74,208]. They were prepared reproducibly by the decomposition of [Ru(COD)(C OT)] (COD=l,5-cyclooctadiene and COT=1,3,5-cyclooctatriene) in THF under 3 bar H2 in the presence of 1 equivalent stabilizer per mole of Ru at room temperature and showed a TOP value of 55 h and a TTO value of 1240 in the dehydrogenation of DMAB at 25 C. The isolability and reusability of ruthenium(O) nanoparticles, two crucial criteria in heterogeneous catalysis, were also tested in the catalytic dehydrogenation of DMAB and it was found that they retain 76% of their initial activity and provide >99% of conversion at the sixth run in the dehydrogenation of DMAB at room temperature. More importantly, ruthenium(0) nanoparticles stabilized by... 

Ott, LS. and Finke, R.G. (2007) Transition-metal nanocluster stabilization for catalysis a critical review of ranking methods and putative... 

The catalyst could be reused with negligible loss of catalytic activity after several runs. Gold nanoclusters, stabilized by the hydrophilic polymer poly(N-vinyl-2-pyrrolidone) (PVP), are also efficient catalyst for aerobic alcohol oxidation in water... 

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