Nanoassemblies of Colloidal Gold Nanoparticles by Oxygen-Induced Inorganic Ligand Replacement

Abstract

This article reports a novel method of the fabrication of floating ultrathin nanoporous films and superlattice-like bottom sediment flakes of colloidal gold nanoparticles (Au NPs) by the oxygen-induced ligand replacement of inorganic species. The two nanoassemblies were realized in a weighing bottle simply by aging the Au colloid, which was synthesized and stabilized using more divalent tin Sn(II) than required for the reduction of HAuCl(4). In situ Raman spectroscopy was employed to trace the assembly process, and we found that the protective Sn(II) species (mostly SnCl(3)(-)) of the gold colloid could be gradually replaced by Cl(-) ions in the solution, while the strongly chemically adsorbed Sn(II) species on the Au NPs was oxidized by O(2) from the air contact. The destabilized colloidal Au NPs by the ligand replacement of SnCl(3)(-) with Cl(-) first assembled into an ultrathin nanoporous film at the air-water interface and then sedimentated to the bottom. Superlattice-like sediment flakes of Au NPs can be obtained at lower temperature (approximately 5 degrees C). Particularly, this method does not involve any organic substances, providing clean ultrathin nanoporous films and superlattice-like flakes of Au NPs. The ultrathin nanoporous films and superlattice-like flakes of Au NPs can serve as SERS substrates with strong and long activity.

Fabrication of nano-network gold films via anodization of gold electrode and their application in SERS

“…These facts imply that the strong SERS effects depend much more on the nanogaps in the nano-networks than on the nano-junctions between the film and the large individual gold nanoparticles. In our previous work [38], purely network-like nanoporous gold films assembled at the air-water interface also showed very strong SERS activity using Py probe molecules, confirming that nanogaps in nano-networks play the key role in the huge enhancement [4,39,40].…”

Facile preparation of ordered arrays of polystyrene spheres dissymmetrically decorated with gold nanoparticles at air/liquid interface and their SERS properties

“…Then 10 mL of sodium dodecyl sulfate (2 wt% in water) was dropped onto the water surface, forming a stable monolayer film of PS spheres. The monolayer film of PS spheres was picked up with a silicon plate, and transferred onto the surface of the Au colloid, which were prepared according to the method previously reported by our group 28 but with reduced volume of precursor solutions (see Table S1 in ESI{). Then the colloid was kept at room temperature (20 uC) or heated to 60 uC for different periods of time without stirring.…”

“…We recently demonstrated that Sn 2+ ions can serve as a reducing agent and stabilizer to prepare Au colloids. 28 Through the oxygen-induced ligand replacement of protective SnCl 3…”

A novel strategy to assemble colloidal gold nanoparticles at the water–air interface by the vapor of formic acid

“…Although there are many contributions on the assembly of NPs at air-water [11,12] and water-oil [13][14][15] interfaces, to our knowledge this is a first report on the assembly of NPs at the air-water interface utilizing vapor of a volatile weak electrolyte. Usually, strong electrolytes resulted in serious aggregation and amalgamation of colloidal NPs in bulk and formation of network-or scrambled-like films at the air-water interface [23][24][25][26]. However, our new strategy of controlling interfacial concentration gradient of electrolyte proposed here can make monolayer films of closepacked gold NPs from colloids in a short period of time without inducing serious aggregation and coagulation.…”

“…Small and 3D network aggregations of Au or Ag NPs were obtained in bulk colloids by adding small amount of NaBH 4 and/or NaCl into the colloids, where electron injection into the NPs in the presence of NaBH 4 decreased the colloidal stability [24]. Recently, we performed a novel assembly of gold [25] or palladium [26] NPs into thin network films at the air-water interface by oxygen-induced ligand replacement of protective SnCl À 3 by aggressive Cl À . We speculate that electrolytes could be employed more sophisticatedly to assemble colloidal NPs at the air-water interface, such as utilizing vapors of weak electrolytes instead of direct addition of strong electrolytes into colloids.…”