Tailored Core−Shell−Shell Nanostructures:  Sandwiching Gold Nanoparticles between Silica Cores and Tunable Silica Shells

Abstract

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.

Preparation of silica stabilized Tobacco mosaic virus templates for the production of metal and layered nanoparticles

“…In the case of silica, the hydroxyl groups on hydrophilic silica surface provide reactive sites that permit interaction with inorganic ions [29][30][31][32]. Alternatively, the use of crosslinking molecules has been extensively investigated to facilitate coatings of gold and silver onto silica particle surfaces [32][33][34][35]. In this paper we examine the application of these techniques on the different silica-coated TMV templates.…”

One-step deposition of Au nanoparticles onto chemically modified ceramic hollow spheres via self-assembly

“…The glass ultramicrotome knife was prepared by breaking a glass strip (1-cm thick) using a knife maker (type 7801A). Ultrathin (80-100 nm) sections of the block were obtained using a diamond knife set at a clearance angle of 6 . The gold coloured sections were captured onto formvar-coated grids by sweeping the section out of the water.…”

“…From the literature, it is seen that a variety of approaches have been used to prepare Au-'Si' composites . There are papers dedicated to adsorbing Au NPs inside [2][3][4][5][6][7][8][9][10][11], outside [12][13][14][15][16][17][18][19][20][21][22][23][24][25] or both sides [25][26][27] of 'Si' spheres. The surface of the 'Si' or template would usually be chemically modified to allow the assembly of Au NPs or AuCl the surfaces of the spheres [29].…”

“…Au NPs can be distributed on the internal surface of a hollow sphere using different methods, i.e. reduction of HAuCl 4(aq) on the inside 'Si' hollow spheres [4], preparation of sacrificial core-Au NP-'Si' or 'Si' core-Au NP-'Si' composite [2,5,6], Au NPs interdispersed inside the 'Si' shell [9] or Au-'Si' core-shell NPs have been assembled on polystyrene spheres [10]. However, the extent of Au NP coverage achieved by these methods is not high.…”

Preparation of hollow multiple-Ag-nanoclustes-C-shell nanostructures and their catalytic properties

“…Such kind of core/shell nanostructures offer protection to the metal cores [29][30][31][32] and are more conveniently to be separated and recycled [33] in terms of catalytic applications. New functionalities can be introduced into these hybrid core/shell nanostructures, which generate a possibility to combine the advantages or distinctive properties of various materials [34].…”