Characterization of Ligand Adsorption at Individual Gold Nanocubes

Abstract

Cetyltrimethylammonium bromide (CTAB) is a widely used surfactant that aids the aqueous synthesis of colloidal nanoparticles. However, the presence of residual CTAB on nanoparticle surfaces can significantly impact nanoparticle applications, such as catalysis and sensing, under hydrated conditions. As such, consideration of the presence and quantity of CTAB on nanoparticle surfaces under hydrated conditions is of significance. Herein, as part of an integrated material characterization framework, we demonstrate the feasibility of in situ atomic force microscopy (AFM) to detect CTAB on the surface of Au nanocubes (Au NCs) under hydrated conditions, which enabled superior characterization compared to conventional spectroscopic methods. In situ force–distance (FD) spectroscopy and Kelvin probe force microscopy (KPFM) measurements support additional characterization of adsorbed CTAB, while correlative in situ AFM and scanning electron microscopy (SEM) measurements were used to evaluate sequential steps of CTAB removal from Au NCs across hydrated and dehydrated environments, respectively. Notably, a substantial quantity of CTAB remained on the Au NC surface after methanol washing, which was detected in AFM measurements but was not detected in infrared spectroscopy measurements. Subsequent electrochemical cleaning was found to be critically important to remove CTAB from the Au NC surface. Correlative measurements were also performed on individual nanoparticles, which further validate the method described here as a powerful tool to determine the extent and degree of CTAB removal from nanoparticle surfaces. This AFM-based method is broadly applicable to characterize the presence and removal of ligands from nanomaterial surfaces under hydrated conditions.

Unraveling the Structural Sensitivity of CO2 Electroreduction at Facet-Defined Nanocrystals via Correlative Single-Entity and Macroelectrode Measurements

“…Nanocrystal morphology was well preserved after the removal of surface ligands following our reported procedures (Figure S9). , Constant-potential electrolysis was conducted to evaluate CO 2 RR activity and selectivity (Figure S10) with a CO 2 -saturated solution of 25 mM KHCO 3 and 10 mM KCl as the electrolyte to better correlate with SECCM studies (see below). Post-mortem SEM images indicated that nanocrystal faceting was well maintained after electrolysis (Figure S11).…”

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth

“…However, due to the detection limit of FTIR, a trace amount of CTAB may remain on the Au nanocubes. Further, CV cycling was conducted in 100 mM HClO 4 to remove additional CTAB from the Au nanocubes as was reported by Choi et al 44…”

Recent Developments in Single-Entity Electrochemistry

“…To address this, Wilson et al removed CTAB bilayers from Au nanowires by heating them on ITO for 1 h in boiling water, enhancing electrochemiluminescence signals . Also, Choi et al achieved effective CTAB removal (evidenced with AFM and SEM characterization) from single Au nanocubes on glassy carbon substrates through a two-step cleaning procedure involving methanol soak and electrochemical cycling . Ramasamy and Ha employed oxygen plasma treatment to remove CTAB from single Au NRs, enhancing their electrocatalytic activity for hydrogen peroxide formation .…”