Gold Nanoparticle Assemblies by Metal Ion−Pyridine Complexation and Their Rectified Quantized Charging in Aqueous Solutions

Abstract

Gold nanoparticle assemblies were constructed by exploiting the complexation interactions between divalent metal ions and pyridine moieties. The thickness (layers) of the particle thin films was readily controlled by the repetition of the alternate dipping cycles, as monitored by quartz crystal microbalance (QCM). Electrochemical studies of these surface-immobilized nanoparticle layers revealed rectified quantized charging characters in aqueous solutions in the presence of hydrophobic anions. The effects of the nature of the electrolyte ions were investigated in the context of their hydrophobicity and interactions with the surface-bound particle molecules. It was found that the onset voltammetric potentials, as well as the effective molecular capacitance of the nanoparticles, were sensitive to the solution compositions. The behaviors were quite similar to those with the nanoparticle assemblies fabricated by dithiol linkages. The present study provided additional experimental parameters that could be used for the manipulation of nanoscale electron transfer.

Chemical manipulations of nanoscale electron transfers

“…Electrochemical quantized capacitance charging was first exemplified by (relatively) monodisperse gold nanoparticles protected by an alkanethiolate monolayer [19][20][21][22][23][24][25][26][27][28][29][30][37][38][39][40][41]. The synthesis of these MPCs was first reported by Schiffrin and co-workers [19] using a biphasic system.…”

“…However, for small and monolayer-protected nanoparticles, the process could be quite tedious, presumably due to steric hindrance [50]. Recently we developed a new two-step procedure involving place-exchange reactions and selfassembling for the efficient surface-immobilization of nanoparticles [37][38][39][40][41]51]. In this approach (Scheme 2), alkanethiolate-protected nanoparticles first undergo surface place-exchange reactions with alkanedithiols of similar chain lengths, rendering the particles surface active with varied copies of peripheral thiol groups.…”

“…These discrete charge transfer processes can also be observed in solutions at ambient temperature, representing an unprecedented class of electrochemical phenomena, namely, electrochemical quantized capacitance charging [19][20][21][22][23][24][25][26][27][28][29][30]. More intriguingly, with electrode-supported nanoparticle organized assemblies, these nanoscale electron transfers can be rectified by simple electrolyte ions [37][38][39][40][41] by virtue of the ion-pair formation between the hydrophobic electrolyte ions and the nanoparticle molecules which leads to the manipulation of the electrode interfacial double-layer capacitance.…”

Ion Limited Charging of Nanoparticle Thin Films

“…The anion influence on the onset potential for film oxidation has been studied in detail. [7][8][9]11,12 The onset potential for the oxidation in voltammetric measurements is dependent on the nature of the anion and shifts to more negative potentials with increasing anion hydrophobicity in the following order: NO 3 -< BF 4 -< ClO 4 -< PF 6 -. 9 This apparent anion rectifying effect has been interpreted in terms of ion association where the oxidized MPC ion pairs with the electrolyte anion.…”

“…9 This apparent anion rectifying effect has been interpreted in terms of ion association where the oxidized MPC ion pairs with the electrolyte anion. [8][9][10]12 The shift in onset potential would then be due to the differing MPC + -anion association constants, with more hydrophobic ions binding more strongly. However, ion association cannot explain why comparable ion-induced rectification is not seen when the films are immersed in lower permittivity solvents such as dichloromethane.…”