Quantized Double-Layer Charging of Highly Monodisperse Metal Nanoparticles

Abstract

We describe unprecedented resolution of electrochemically observed quantized double layer (QDL) charging, attained with use of reduced solution temperatures and with an annealing procedure that produces hexanethiolate monolayer protected gold clusters (C6 MPCs) with a high level of monodispersity in charging capacitance, C(CLU). The spacing DeltaV = e/C(CLU) on the electrochemical potential axis between one electron changes in the electronic charge of nanoscopic metal particles is determined by their effective capacitance C(CLU). The high monodispersity of the C6 MPCs with Au(140) cores facilitates (a) detailed rotated disk and cyclic voltammetric measurements, (b) simulation of QDL waveshapes based on assumed reversible, multivalent redox-like behavior, (c) determination of nanoparticle diffusion rates, and (d) observation of as many as 13 changes in the MPC charge state, from MPC(6-) to MPC(7+). The single electron QDL charging peaks are quite evenly spaced (DeltaV constant) at potentials near the MPC potential of zero charge, but are irregularly spaced at more positive and negative potentials. The irregular spacing is difficult to rationalize with classical double layer capacitance ideas and is proposed to arise from a correspondingly structured (e.g., not smooth) density of electronic states of the nanoparticle core, resulting from its small HOMO/LUMO gap and incipiently molecule-like behavior.

Solvent Effect on Redox Properties of Hexanethiolate Monolayer-Protected Gold Nanoclusters

“…14 Finally, a fraction of MPCs that are ethanol soluble with a mean diameter of 1.6 ( 0.4 nm in the metallic core were obtained as demonstrated previously. 12 2.3.…”

“…In general, the values of D are within a range of 2.0-4.0 × 10 -6 cm 2 s -1 , which is in good agreement with those reported previously. 14 …”

Absolute Standard Redox Potential of Monolayer-Protected Gold Nanoclusters

“…31 The MPCs were prepared by the Brust reaction 1,2 followed by extraction and annealing processes to harvest a population of MPCs with relatively uniform metallic cores. 16 Briefly, 1.55 g of HAuCl 4 ‚3H 2 O in water was mixed with 1.12 g of TOABr in toluene under vigorous stirring. After AuCl 4 -was completely extracted into toluene, 1.8 mL C6-SH corresponding to a 3:1 molar ratio (S/Au) was added.…”

“…[3][4][5][6] At ambient temperature, both freely diffusing and electrode-attached MPCs demonstrate the voltammetric responses featuring a series of evenly spaced current peaks. 4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] This ensemble behavior is equivalent to a series of classical Coulomb staircase charging events or sequential electrochemical redox reactions, which occur as MPCs encompass an intermediate dimension between small molecules and bulk materials. Previously, the sequential electrontransferhasbeenobservedforfullerene(andderivatives) [22][23][24][25][26] and Pt-carbonyl nanoclusters [Pt n (CO) m ], [27][28][29] which led Weaver et al 30 to develop an electrostatic model to relate the electron transfer energetics of molecular capacitances in gas-and solution-phase systems.…”

Atomistic Simulations of Functional Au144(SR)60 Gold Nanoparticles in Aqueous Environment

“…3,47−50 The structural model of Au 144 (SR) 60 is based on the recent theoretical model by LopezAcevedo et al 51 which was shown to be in very good agreement with the experimental X-ray powder diffraction measurements, 52 and the AuNP electronic structure is consistent with the chemical voltammetry measurements and optical properties. 43,53,54 We discuss several aspects of electrostatics in systems comprised of charged nanoparticles and ions in aqueous environments. We consider the ordering and dynamics of ions and water around AuNPs, and the range of water-mediated interactions between AuNPs and other objects.…”