Heating-Induced Evolution of Thiolate-Encapsulated Gold Nanoparticles:  A Strategy for Size and Shape Manipulations

Abstract

A heating treatment strategy for inducing size and shape change of composite nanoparticles in solutions is described. The composite nanoparticles are ∼2 nm gold cores encapsulated with alkanethiolate monolayers. The development of abilities in size and shape controls constitutes the motivation of this work. We demonstrated a remarkable evolution of the preformed particles in solutions toward monodispersed larger core sizes with well-defined and highly faceted morphologies. The particles thus evolved were encapsulated with the thiolate shells, and exhibited striking propensities of forming long-range ordered arrays. The morphological and structural evolutions were characterized using transmission electron microscopy, X-ray diffraction, UV−vis and infrared spectroscopies. Although temperature-driven crystal growth is known for nonencapsulated particles, the evolution of the thiolate-encapsulated nanoparticles in solutions into well-defined morphologies represents an intriguing example of temperature manipulations in size monodispersity and shape control.

Synthesis, processing, assembly and activation of core-shell structured gold nanoparticle catalysts

“…It is known that melting starts at the surface layer where the solid core is in equilibrium with the surrounding liquid shell. The temperature-correlation of melting predicts that the lowering of melting point is inversely proportional to the particle size (18). In comparison with a melting temperature of 1320 K for bulk gold, gold particles of 2.5 nm diameter are predicted to melt at ~5 00 K. The surface melting temperature could be even lower, and the temperature change is also related to the capping-dominated surface tension.…”

“…The two-phase synthesis protocol developed by Schiffrin and co-workers (16-17) is now widely used for fabricating stable and soluble gold and alloy nanoparticles of a few nanometers in core diameter, which is briefly described in the Experimental section. The nanocrystal cores can be re-sized or re-shaped in a solution by a thermally-activated processing protocol developed recently in our laboratory (18)(19). Briefly, the processing starts from the pre-synthesized nanoparticles (1-2 nm) in concentrated solutions and molten salt solutions by thermally inducing desorption of capping molecules, coalescence of nanocrystal cores and re-encapsulation.…”

“…The exothermic process due to a significant increase of temperature within the particle (20) could be extremely important in the coalescence process by reducing the coalescence time by as much as a few orders of magnitude. Gold and alloy nanoparticles in the 1-10 nm range have been successfully prepared using this thermal processing protocol (18)(19)(21)(22)(23)(24).…”

Electrocatalytic reduction of oxygen: Gold and gold-platinum nanoparticle catalysts prepared by two-phase protocol

“…Unlike some of our earlier electrocatalytic studies in which gold nanoparticles were assembled on planar glassy carbon electrodes (20)(21)(22)(23)(24), the gold and gold-platinum nanoparticles with different bimetallic ratios prepared by two-phase protocol (32)(33)(34)(35) are assembled on carbon black support materials and activated by calcination. More importantly, we have attempted an initial comparison of the electrocatalytic ORR activities of our carbon-supported Au and AuPt nanoparticle catalysts with commercially-available Pt/C and PtRu/C catalysts (E-tek) under the same voltammetric measurement conditions.…”

Self-assembly of nanoparticles employing polymerization-induced phase separation

“…For example, a POSS cube with 7 isobutyl groups and 1 glycidyloxypropyl group at its corners could be dissolved at high temperatures in epoxy precursors based on stoichiometric amounts of diglycidylether of bisphenol A (DGEBA) and 4,4' methylenebis(2,6-diethylaniline) 6 (MDEA) [3]. The morphologies arising from PIPS will depend on the composition of the blend and the polymerization temperature.…”