Article

New preparation method of gold nanoparticles on SiO2.

Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México (UNAM), Circuito Exterior S/N, A. P. 70-186, C. P. 04510, Ciudad Universitaria, México D. F., Mexico. zanella@ aleph.cinstrum.unam.mx
The Journal of Physical Chemistry B (Impact Factor: 3.61). 06/2006; 110(17):8559-65. DOI: 10.1021/jp060601y
Source: PubMed

ABSTRACT It is shown that adsorption of the [Au(en)(2)](3+) cationic complex can be successfully employed for the deposition of gold nanoparticles (1.5 to 3 nm) onto SiO(2) with high metal loading, good dispersion, and small Au particle size. When the solution pH increases (from 3.8 to 10.5), the Au loading in the Au/SiO(2) samples increases proportionally (from 0.2 to 5.5 wt %), and the average gold particle size also increases (from 1.5 to 2.4 nm). These effects are explained by the increase in the amount of negatively charged sites present on the SiO(2) surface, namely, when the solution pH increases, a higher number of [Au(en)(2)](3+) species can be adsorbed. Extending the adsorption time from 2 to 16 h gives rise to an increase in the gold loading from 3.3 to 4.0 wt % and in the average particle size from 1.8 to 2.9 nm. Different morphologies of gold nanoparticles are present as a function of the particle size. Particles with a size of 3-5 nm show defective structure, some of them having a multiple twinning particle (MTP) structure. At the same time, nanoparticles with an average size of ca. 2 nm exhibit defect-free structure with well-distinguishable {111} family planes. TEM and HAADF observations revealed that Au particles do not agglomerate on the SiO(2) support: gold is present on the surface of SiO(2) only as small particles. Density functional theory calculations were employed to study the mechanisms of [Au(en)(2)](3+) adsorption, where neutral and negatively charged silica surfaces were simulated by neutral cluster Si(4)O(10)H(4) and negatively charged cluster Si(4)O(10)H(3), respectively. The calculation results are totally consistent with the suggestion that the deposition of gold takes place according to a cationic adsorption mechanism.

0 Bookmarks
 · 
74 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An aero-self-assembly to fabricate Au-SiO2 /IBU-PLL functional nanobunches is introduced for the first time for the efficient inhibition of cell proliferation through NIR-induced chemo-thermal therapy. This functional nanoparticle design approach provides useful insights for improving the applica-bility of Au-based hybrid nanoparticles for the development of smart controlled release systems.
    Small 06/2014; · 7.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The heterogenization of homogeneous catalysts is a current topic in sustainable chemistry and catalysis. Such immobilized molecular catalysts provide access to environmentally benign chemical syntheses due to the ease of product separation and concomitant waste decrease. This perspective focuses on the fabrication of nanostructured catalysts by using amorphous (non)porous silica or metal oxides and periodic mesoporous (organo)silicas PM(O)S as 1(st) and 2(nd) generation supports, respectively, as well as metal (silyl)amide complexes as tailor-made grafting precursors. The pertinent SOMC (SOMC = surface organometallic chemistry) places special emphasis on organometallic hybrid materials that display properties distinct from the respective molecular catalysts and on new catalytic avenues which originate from 2(nd) generation supports.
    Dalton Transactions 07/2013; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The unique interfacial sites of Au nanoparticles supported on TiO2 are known to catalyze the activation of oxygen and it's addition to small molecules including H2, CO, NO and propylene. Herein we extend these ideas and show that the unique Au-Ti dual perimeter sites that form at the Au/TiO2 interface can also catalyze more demanding C-H and C-O bond activation reactions involved in the deoxygenation organic acids such as acetic acid. We have shown previously that acetic acid can be partially oxidized on a Au/TiO2 catalyst to form a novel gold ketenylidene (Au2==C==C==O) intermediate. In the present work we use in situ infrared spectroscopy and first-principle density functional theory (DFT) to examine the mechanism and the kinetics by which this reaction proceeds. The reaction was found to be localized at the dual perimeter sites of the Au/TiO2 catalyst, where 02 was activated. In contrast to Au/TiO2, no ketenylidene formation was observed on a similar Au/SiO2 catalyst or a TiO2 blank sample. The reaction involves the activation of multiple C-H bonds as well as the C-O bond in the adsorbed CH3COO species. C-O bond scission is postulated to occur at the TiO2 sites, while C-H bond scission occurs on Au sites, both near the active Au-Ti4+ dual perimeter sites. 18O2 isotopic labeling indicated that the O moiety of the ketenylidene species originates from the acetic acid during the oxidation process involving molecular O2. The rate-limiting step was found to be the C--O bond scission resulting in an apparent overall activation energy of 1.72 eV as determined from DFT calculations. This is in very good agreement with the experimentally measured apparent activation energy of 1.7 +/- 0.2 eV. A deuterium kinetic isotope effect of approximately 4 indicates that C-H bond activation is kinetically involved in the overall acetate oxidation reaction.
    Faraday Discussions 01/2013; 162:247-65. · 3.82 Impact Factor