Persistent Multilayer Electrode Adsorption of Polycationic Au Nanoparticles

Abstract

Multilayers of mixed monolayer thiolate-protected Au nanoparticles with polycationic ligand shells are strongly and persistently adsorbed on Pt electrodes from dilute CH 3 CN/electrolyte solutions of the nanoparticles. The adsorption is so robust that the electrodes can be transferred, with rinsing, to nanoparticle-free CH 3 CN/ electrolyte (and other organic solvents) and their voltammetry observed without significant desorption. The nanoparticles have the average composition [Au 225 (TEA-thiolateThe cation sites are a quaternary ammonium-terminated ligand (TEA-thiolate + ) -S(CH 2 ) 11 N(CH 2 CH 3 ) 3 + ). The ferrocene content of the ligand shell (Y) allows voltammetric detection of the adsorption, and also affects it. This work describes how the extent of nanoparticle adsorption (surface coverage, Γ NP mol/cm 2 ) depends on the manner of exposure of the electrode (with potential scanning, at a fixed potential, or at open circuit) to the nanoparticle solution, and on the nanoparticle concentration, the electrolyte and its concentration, and on the mixed monolayer composition. Increase of the cationic TEA-thiolate + component of the mixed monolayer from X ) 18 to 27 increases, for a given exposure mode, the attained amount of adsorption from < one monolayer to > two monolayers, and broadens the voltammetric wave. The adsorption phenomenon is interpreted as induced by multiple ion-pair bridges between cation sites and electrolyte anions, and as such represents an entropic consequence of multiple interactions between nanoparticles and between nanoparticles and the electrode.

Tunable Aminooxy‐Functionalized Monolayer‐Protected Gold Clusters for Nonpolar and Aqueous Oximation Reactions

“…For example, after reaction of Au(C 6 S)( AOT ) MMPCs with ferrocene (Fc)‐carboxaldehyde ( Figure A), electrochemical measurements on the Fc‐derivatized MMPCs in solution (Figure B, red CV) demonstrated oxidation/reduction behavior characteristic of ferrocene. The small 45 mV peak splitting and symmetric waves indicate that the Au(C 6 S)( AOT‐ ferrocene) MMPCs are strongly adsorbed to the Pt working electrode surface, similar to previous results on other Fc‐MPCs with high loading . A CV of the working electrode after removal from the solution of Au(C 6 S)( AOT‐ ferrocene) MMPCs and placing in solvent and electrolyte only (Figure B, blue CV) confirms strong adsorption of these MMPCs to the electrode surface since the Fc peaks remain in the CV and they are symmetric with small peak splitting.…”

“…The small 45 mV peak splitting and symmetric waves indicate that the Au(C 6 S)(AOT-ferrocene) MMPCs are strongly adsorbed to the Pt working electrode surface, similar to previous results on other Fc-MPCs with high loading. [35,36] A CV of the working electrode after removal from the solution of Au(C 6 S)(AOT-ferrocene) MMPCs and placing in solvent and electrolyte only ( Figure 4B, blue CV) confirms strong adsorption of these MMPCs to the electrode surface since the Fc peaks remain in the CV and they are symmetric with small peak splitting. The fluorophore 1-pyrenecarboxaldehyde was attached to the Au(C 6 S)(AOT) MMPCs by simple mixing and the fluoresence of the resulting MMPCs was measured.…”

“…Charact. 2019, 36,1900093 www.advancedsciencenews.com www.particle-journal.com provides an approximate cluster molecular formula when combined with the known cluster diameter.…”

“…Charact. 2019, 36,1900093 rendering the Au MMPCs water-soluble (Scheme 3), and reacted efficiently with the water-soluble aldehydes to yield the corresponding oxime ether adducts as mixtures of E/Z isomers ( Figures 2E and 3A). In the case of propanal, neutralization of the adduct solution by washing with basic buffer restored the organic solubility and enabled extraction of the derivatized MMPCs into organic solvent for ease of isolation.…”

“…Charact. 2019, 36,1900093 (SC 6 www.advancedsciencenews.com www.particle-journal.com for 20 min using a stream of argon before heating the solution at reflux for 20 h. The reaction mixture was then cooled to rt, quenched with diethyl ether (10 mL) and concentrated by rotary evaporation to afford the crude product, which was dissolved in CHCl 3 (20 mL…”