In Situ Non-DLVO Stabilization of Surfactant-Free, Plasmonic Gold Nanoparticles: Effect of Hofmeister鈥檚 Anions

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• 作者：Vivian Merk ; Christoph Rehbock ; Felix Becker ; Ulrich Hagemann ; Hermann Nienhaus ; Stephan Barcikowski
• 刊名：Langmuir
• 出版年：2014
• 出版时间：April 22, 2014
• 年：2014
• 卷：30
• 期：15
• 页码：4213-4222
• 全文大小：496K
• 年卷期：v.30,no.15(April 22, 2014)
• ISSN：1520-5827

文摘

Specific ion effects ranking in the Hofmeister sequence are ubiquitous in biochemical, industrial, and atmospheric processes. In this experimental study specific ion effects inexplicable by the classical DLVO theory have been investigated at curved water鈥搈etal interfaces of gold nanoparticles synthesized by a laser ablation process in liquid in the absence of any organic stabilizers. Notably, ion-specific differences in colloidal stability occurred in the H眉ckel regime at extraordinarily low salinities below 50 渭M, and indications of a direct influence of ion-specific effects on the nanoparticle formation process are found. UV鈥搗is, zeta potential, and XPS measurements help to elucidate coagulation properties, electrokinetic potential, and the oxidation state of pristine gold nanoparticles. The results clearly demonstrate that stabilization of ligand-free gold nanoparticles scales proportionally with polarizability and antiproportionally with hydration of anions located at defined positions in a direct Hofmeister sequence of anions. These specific ion effects might be due to the adsorption of chaotropic anions (Br^{鈥?/sup>, SCN鈥?/sup>, or I鈥?/sup>) at the gold/water interface, leading to repulsive interactions between the partially oxidized gold particles during the nanoparticle formation process. On the other hand, kosmotropic anions (F鈥?/sup> or SO₄2鈥?/sup>) seem to destabilize the gold colloid, whereas Cl鈥?/sup> and NO₃鈥?/sup> give rise to an intermediate stability. Quantification of surface charge density indicated that particle stabilization is dominated by ion adsorption and not by surface oxidation. Fundamental insights into specific ion effects on ligand-free aqueous gold nanoparticles beyond purely electrostatic interactions are of paramount importance in biomedical or catalytic applications, since colloidal stability appears to depend greatly on the type of salt rather than on the amount.}