Gold nanoparticles mechanism

The use of a lipophilic zinc(II) macrocycle complex, 1-hexadecyl-1,4,7,10-tetraazacyclododecane, to catalyze hydrolysis of lipophilic esters, both phosphate and carboxy (425), links this Section to the previous Section. Here, and in studies of the catalysis of hydrolysis of 4-nitrophenyl acetate by the Zn2+ and Co2+ complexes of tris(4,5-di-n-propyl-2 -imidazolyl)phosphine (426) and of a phosphate triester, a phos-phonate diester, and O-isopropyl methylfluorophosphonate (Sarin) by [Cu(A(A(A/,-trimethyl-A/,-tetradecylethylenediamine)l (427), various micellar effects have been brought into play. Catalysis of carboxylic ester hydrolysis is more effectively catalyzed by A"-methylimidazole-functionalized gold nanoparticles than by micellar catalysis (428). Other reports on mechanisms of metal-assisted carboxy ester hydrolyses deal with copper(II) (429), zinc(II) (430,431), and palladium(II) (432). 

In a recent review, Haruta has reassessed the mechanism of CO oxidation on the basis of the Bond and Thompson and Kung models, i.e. that the CO is activated by adsorption on Au° on the surface of the gold nanoparticles and that dioxygen is activated by the atoms at the periphery between the support and the gold nanocrystals (Fig. 4.7). The atoms at the periphery are proposed by Haruta to be cationic in nature, possibly Au(OH)s or Au(OH) formed by the presence of water vapor that is essential for the observed high activity catalysts. It is clear that the debate will continue for the immediate future. There are two reasons why finding an answer to the key question of the nature of the active site in gold catalysts for CO oxidation. The first is purely scientific... 

This chapter is divided into three parts. Firstly, the catalytic activities and stabilities of gold nanoparticles supported on allotropic Ti02 phases are compared. To understand the mechanism of catalysis of the gold nanoparticles deposited on metal... 

The formation of Au-OHad or surface oxides on gold in alkaline electrolyte was in fact proposed to explain some of the electrocatalytic properties observed for a gold electrode (e.g., incipient hydrous oxide/adatom mediator model ). Our previous measurement of the interfacial mass change also indicated the formation of Au oxides (AU2O3, AuOHorAu(OH)3) on gold nanoparticle surfaces. A detailed delineation of the catalytic mechanism is part of our on-going work. 

Cao L, Liu Z, Zhu T (2006) Eormation Mechanisms of Non-Spherical Gold Nanoparticles During Seeding Growth Roles of Anion Adsorption and Reduction Rate. J Colloid Interface Sci 293 67-69... 

Chitosan-stabilized Au NPs can be selectively synthesized on surfaces like poly (dimethylsiloxane) (PDMS) films using HAuC14 as precursor. The computation of surface plasmon bands (SPBs) based on Mie theory and experimental results indicates that the particles are partially coated by chitosan. The proposed mechanism implies that chitosan acts as a reducing/stabilizing agent. Furthermore, PDMS films patterned with chitosan could induce localized synthesis of gold nanoparticles in regions capped with chitosan only [110]. 

Figure 3.24 Molecular mechanism of glucose oxidation with gold nanoparticles (Au/C) [175].

TianY,TatsumaT. Mechanisms and applications of plasmon-induced charge separation at Ti02 films loaded with gold nanoparticles. J Am Chem Soc 2005 127 7632-7. 

Schrinner M, Polzer F, Mei Y, Lu Y, Haupt B, Ballauff M, Goldel A, Drechsler M, Preussner J, Glatzel U (2007) Mechanism of the formation of amorphous gold nanoparticles within spherical polyelectrolyte brushes. Macromol Chem Phys 208 1542-1547... 

The mechanistic aspect of the fungal reduction of metal ions led by colloidal suspension is still an open question. However, in the fungal case, this process occurs probably either by reductase action or by electron shuttle quinines, or both. To elucidate the mechanism of nanoparticles formation, a novel fungal/enzyme-based in vitro approach was for the first time explained by Mukherjee et al. (2002). They successfully used species-specific NADH-dependent reductase, released by the F. oxysporum, to carry out the reduction of AuClJ ions to gold nanoparticles. Duran et al. (2005) later reported that the reduction of the metal ions occnrs by a nitrate-dependent reductase and a shuttle quinone extracellular process. The same... 

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