Effect of Postsynthesis Purifications on Gold and Silver Nanoparticle Ligand Coverage
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- 作者：Siyam M. Ansar ; Fiaz S. Mohammed ; Gregory von White II ; Maeve Budi ; Kristin Conrad Powell ; O. Thompson Mefford ; Christopher L. Kitchens
- 刊名：Journal of Physical Chemistry C
- 出版年：2016
- 出版时间：March 31, 2016
- 年：2016
- 卷：120
- 期：12
- 页码：6842-6850
- 全文大小：482K
- ISSN：1932-7455
文摘
Wet chemical nanoparticle synthesis is commonly employed because of the ability to tailor and control nanoparticle size, shape, polydispersity, and surface chemistry; however, excess ligands or free surfactants in the colloidal dispersion can be detrimental for many nanoparticle applications. Postsynthesis purification using antisolvent precipitation is a widely employed method to remove the excess ligands or precursors; however, there has been little in-depth fundamental investigation of the dynamics between the nanoparticle, ligand, and dispersing media as well as the morphology and fate of the nanoparticle and ligands during nanoparticle processing. In this paper, we investigate the changes in ligand surface coverage for dodecanethiol-stabilized gold and silver nanoparticles in response to repetitive antisolvent precipitation and redispersion using gas chromatography, thermogravimetric analysis, and small-angle neutron scattering. These techniques were each used to determine percent surface coverage and equilibrium ligand partitioning between the nanoparticle surface and bulk solution, which was then modeled with the Langmuir isotherm to determine the binding free energy. The binding free energy for dodecanethiol on 4.2 nm diameter gold nanoparticles was found to be −23 kJ/mol by gas chromatography (GC) and −34 kJ/mol by small-angle neutron scattering (SANS). The binding free energy for dodecanethiol on 7.7 nm diameter silver nanoparticles was found to be −21 kJ/mol by TGA and −29 kJ/mol by SANS. While these numbers demonstrate variability based on the method, they are comparable to literature values. Other notable results from this work demonstrate the optimization of the purification process and avoidance of using excess antisolvent which can lead to coprecipitation of the excess ligand with the nanoparticles, hindering the purification. Finally, multiple techniques for determining ligand binding free energy are demonstrated as well as evaluation of the pros and cons of each method.