Oxidation-Induced Self-Assembly of Ag Nanoshells into Transparent and Opaque Ag Hydrogels and Aerogels

Abstract

The synthesis of hollow Ag nanoshells (NSs) with tunable plasmon bands in the visible spectrum and their oxidative-assembly into high-surface-area, mesoporous, transparent, and opaque Ag gel frameworks is reported. Thiolate-coated Ag NSs with varying size and shell thickness were prepared by fast chemical reduction of preformed Ag2O nanoparticles (NPs). These NSs were assembled into monolithic Ag hydrogels via oxidative removal of the surface thiolates, followed by CO2 supercritical drying to produce metallic Ag aerogels. The gelation kinetics have been controlled by tuning the oxidant/thiolate molar ratio (X) that governs the rate of NP condensation, which in turn determines the morphology, optical transparency, opacity, surface area, and porosity of the resultant gel frameworks. The monolithic Ag hydrogels prepared using high concentration of oxidant (X > 7.7) leads to oxidative etching of precursor colloids into significantly smaller NPs (3.2-7.6 nm), which appeared to eliminate the visible light scattering yielding transparent gel materials. In contrast, the opaque Ag aerogels composed entirely of hollow NSs exhibit enormously high surface areas (45-160 m(2)/g), interconnected meso-to-macro-pore network that can be tuned by varying the inner cavity of Ag colloids, and accessibility of chemical species to both inner and outer surface of the hollows, offering perspectives for a number of new technologies. An advantage of current synthesis is the ability to transform Ag NSs into monolithic hydrogels within 4-12 h, which otherwise is reported to require weeks to months for the oxidation-induced metallic gel synthesis reported to date.

Modern Inorganic Aerogels

“…[102][103][104][105] Thei nitial nanoshells are produced via ag alvanic replacement reaction of pre-formed Ag and Ni nanoparticles,respectively.Au/Ag, Pd/ Ag, and Pt/Ag alloyed nanoshells were first concentrated by either simple solvent evaporation or with the help of centrifuge membrane filters.Colloidal solutions concentrated through solvent evaporation spontaneously formed ag el when stored in the dark for several days,w hereas the nanoshell solution concentrated with centrifuge filters could be destabilized by the addition of NaCl. [102][103][104][105] Thei nitial nanoshells are produced via ag alvanic replacement reaction of pre-formed Ag and Ni nanoparticles,respectively.Au/Ag, Pd/ Ag, and Pt/Ag alloyed nanoshells were first concentrated by either simple solvent evaporation or with the help of centrifuge membrane filters.Colloidal solutions concentrated through solvent evaporation spontaneously formed ag el when stored in the dark for several days,w hereas the nanoshell solution concentrated with centrifuge filters could be destabilized by the addition of NaCl.…”

Function‐Led Design of Aerogels: Self‐Assembly of Alloyed PdNi Hollow Nanospheres for Efficient Electrocatalysis

“…[4] Arachchige et al expanded Ag-based metallic aerogels into controlled morphologies. [5] Meanwhile,our group has reported on aseries of pure and mixed aerogels (made of noble metals,s emiconductors,a nd quantum dots). [6] Thea erogels reported up to now have shown great application potential in the areas of catalysis,energy storage,and thermoresistors.…”

Nanostructuring Noble Metals as Unsupported Electrocatalysts for Polymer Electrolyte Fuel Cells

“…[52] Thiolate-coated Ag nanoshells with varying size and shell thickness were then assembled into monolithic hydro/aerogels via oxidative removal of the surface thiolates. [53] By taking advantage of hydrogel engineering, PtAg nanotubular aerogels were fabricated via a simple galvanic replacement reaction between the in situ, spontaneously gelated Ag hydrogel and the Pt precursor. [43] As shown in Figure 4g-i, the resulting PtAg aerogels possess hierarchical porous network features with primary macro-pores from the aerogel network and secondary micro-pores from the porous surface of the nanotube-backbones, resulting in high porosities and large specific surface areas.…”