Citrate Coordination and Bridging of Gold Nanoparticles: The Role of Gold Adatoms in AuNP Aging.

David-Benjamin Grys,Bart De Nijs,Wenting Wang,Junyang Huang,Andrew R Salmon,Jeremy J Baumberg,Wei-Hsin Chen,Oren A Scherman

doi:10.1021/acsnano.0c03050

Abstract

Gold nanoparticles used in many types of nanostructure are mostly stabilized by citrate ligands. Fully understanding their dynamic surface chemistry is thus essential for applications, particularly since aging is frequently a problem. Using surface-enhanced Raman spectroscopy in conjunction with density functional theory calculations, we are able to determine Au–citrate coordination in liquid with minimal invasiveness. We show that citrate coordination is mostly bidentate and simply controlled by its protonation state. More complex binding motifs are caused by interfering chloride ions and gold adatoms. With increasing age of stored gold nanoparticle suspensions, gold adatoms are found to move atop the Au facets and bind to an additional terminal carboxylate of the citrate. Aged nanoparticles are fully refreshed by removing these adatoms, using etching and subsequent boiling of the gold nanoparticles.

Highlights

Gold nanoparticles used in many types of nanostructure are mostly stabilized by citrate ligands
We employ SERS, which is advantageous compared to previous techniques, as it records the vibrational signatures of citrate anions directly in the liquid state and exclusively at the metal interfaces of colloidal gold nanoparticles
To probe the surface chemistry using SERS, the gold nanoparticles are aggregated into clusters with the help of the linker molecule cucurbit[5]uril (CB[5]), which acts as a precise molecular spacer (Figure 1a, ii, see Figure S2 for alternative salt aggregation)

Summary

Introduction

Gold nanoparticles used in many types of nanostructure are mostly stabilized by citrate ligands Understanding their dynamic surface chemistry is essential for applications, since aging is frequently a problem. ACS Nano www.acsnano.org the need for aggregating agents allow us to record SERS spectra in the absence of chloride and citrate decomposition products. By this method, we provide strong evidence that the timeand temperature-dependent rearrangement of citrate anions (from μ2 to μ4, c2 to c2t2, see Figure S6 for details on custom notation) on the AuNP surface (aging) is driven by migration of Au adatoms on the facet.

Methods

Results

Conclusion