Using Post Synthetic Treatment of AuNPs to Improve Uniformity of Their Thiol Ligand Coverage and Electronic Properties

Gold nanoparticles are valued for their unique electronic properties and electronic structure as well as the tunability of their size and surface chemistry. However, there exist a number of open questions regarding the connection among size, morphology, surface chemistry, and electronic structure. Herein, we report a study that tracks changes in these aspects for small (∼3 nm diameter) hexanthiolate-protected gold nanoparticles aged in a dialysis bag that allowed free diffusion of ligand, but not metallic core. Using TEM, we find that statistically significant changes in size accompany aging. Using inductively coupled plasma atomic/optical emission spectroscopy, we find that statistically significant changes in the ligand-to-gold ratio accompany aging. Finally using a modified Evans NMR technique, we observe that statistically significant changes in the electronic structure accompany aging. Examining all these aspects, we conclude that the only meaningful connection between them is that both the ligand-to-gold ratio and the electronic structure properties experience a “focusing” in their values during aging, meaning that the standard deviation in these values decreases. We therefore suggest that during aging, the nanoparticles undergo a restructuring that leads to this focusing of the electronic structure. Additionally, we demonstrate that this dialysis treatment is an effective means to obtain particles with a more consistent electronic structure at the population level.