Bischoff Marie, Biriukov Denys, Předota Milan, Marchioro Arianna
Laboratory for fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 16610 Prague 6, Czech Republic.
J Phys Chem C Nanomater Interfaces. 2021 Nov 18;125(45):25261-25274. doi: 10.1021/acs.jpcc.1c07191. Epub 2021 Nov 9.
Ion-specific effects play a crucial role in controlling the stability of colloidal systems and regulating interfacial processes. Although mechanistic pictures have been developed to explain the electrostatic structure of solid/water colloidal interfaces, ion-specific effects remain poorly understood. Here we quantify the average interfacial water orientation and the electrostatic surface potential around 100 nm SiO and TiO colloidal particles in the presence of NaCl, RbCl, and CaCl using polarimetric angle-resolved second harmonic scattering. We show that these two parameters can be used to establish the ion adsorption mechanism in a low ionic strength regime (<1 mM added salt). The relative differences between salts as a function of the ionic strength demonstrate cation- and surface-specific preferences for inner- vs outer-sphere adsorption. Compared to monovalent Rb and Na, Ca is found to be preferentially adsorbed as outer-sphere on SiO surfaces, while a dominant inner-sphere adsorption is observed for Ca on TiO. Molecular dynamics simulations performed on crystalline SiO and TiO surfaces support the experimental conclusions. This work contributes to the understanding of the electrostatic environment around colloidal nanoparticles on a molecular level by providing insight into ion-specific effects with micromolar sensitivity.
离子特异性效应在控制胶体系统的稳定性和调节界面过程中起着至关重要的作用。尽管已经提出了一些机理模型来解释固体/水胶体界面的静电结构，但离子特异性效应仍未得到充分理解。在这里，我们使用偏振角分辨二次谐波散射来量化在存在氯化钠、氯化铷和氯化钙的情况下，100纳米二氧化硅和二氧化钛胶体颗粒周围的平均界面水取向和静电表面电位。我们表明，这两个参数可用于在低离子强度范围（添加盐浓度<1 mM）内建立离子吸附机制。盐之间的相对差异作为离子强度的函数，表明了阳离子和表面对内层与外层吸附的特异性偏好。与单价铷和钠相比，发现钙在二氧化硅表面优先以外层形式吸附，而在二氧化钛上观察到钙主要以内层形式吸附。在结晶二氧化硅和二氧化钛表面进行的分子动力学模拟支持了实验结论。这项工作通过提供对具有微摩尔灵敏度的离子特异性效应的深入了解，有助于在分子水平上理解胶体纳米颗粒周围的静电环境。
