Revealing the etching process of water-soluble Au25 nanoclusters at the molecular level

Yitao Cao,Bihan Zhang,Tongyu Liu,Jianping Xie,Tiankai Chen,De-En Jiang

doi:10.1038/s41467-021-23568-0

Abstract

Etching (often considered as decomposition) is one of the key considerations in the synthesis, storage, and application of metal nanoparticles. However, the underlying chemistry of their etching process still remains elusive. Here, we use real-time electrospray ionization mass spectrometry to study the reaction dynamics and size/structure evolution of all the stable intermediates during the etching of water-soluble thiolate-protected gold nanoclusters (Au NCs), which reveal an unusual “recombination” process in the oxidative reaction environment after the initial decomposition process. Interestingly, the sizes of NC species grow larger and their ligand-to-metal ratios become higher during this recombination process, which are distinctly different from that observed in the reductive growth of Au NCs (e.g., lower ligand-to-metal ratios with increasing sizes). The etching chemistry revealed in this study provides molecular-level understandings on how metal nanoparticles transform under the oxidative reaction environment, providing efficient synthetic strategies for new NC species through the etching reactions.

Highlights

Etching is one of the key considerations in the synthesis, storage, and application of metal nanoparticles
To exclude all other by-products and small complexes that could affect the etching process as well as the real-time electrospray ionization mass spectrometry (ESI-MS) measurement, we purified the product by ultrafiltration and polyacrylamide gel electrophoresis (PAGE)
The pH value of the solution is maintained at 9.10 ± 0.20, because this pH can provide the best signal in the ESI-MS measurement, and the pH value remained almost unchanged during the reaction (Supplementary Fig. 1)

Summary

Introduction

Etching (often considered as decomposition) is one of the key considerations in the synthesis, storage, and application of metal nanoparticles. We use real-time electrospray ionization mass spectrometry to study the reaction dynamics and size/structure evolution of all the stable intermediates during the etching of water-soluble thiolate-protected gold nanoclusters (Au NCs), which reveal an unusual “recombination” process in the oxidative reaction environment after the initial decomposition process. The etching chemistry revealed in this study provides molecular-level understandings on how metal nanoparticles transform under the oxidative reaction environment, providing efficient synthetic strategies for new NC species through the etching reactions. As etching is a reversed process of growth, the comparison of both processes at molecular level may further reveal the fundamental aspects of the formation and transformation of metal NCs under either reductive or oxidative reaction environment. Our findings shed light into how metal nanoparticles transform in oxidative environment at molecular level and provide guidance to synthesize new NC species by etching reactions

Methods

Results

Conclusion