Quantifying Specific Ion Effects on the Surface Potential and Charge Density at Silica Nanoparticle–Aqueous Electrolyte Interfaces

Abstract

The surface charge density and surface potential of oxide surfaces are to a large extent regulated by the co-and counterion distributions in the electrical double layer. Here we study the effect of different anions (Cl − , Br − , I − , HCOO − and NO 3 − ) in sodium electrolytes and different cations (Li + , Na + , K + and Cs + ) in chloride electrolytes on the surface charge density and relative surface potential of colloidal nanometer sized silica (SiO 2 ) as a function of electrolyte concentration and bulk pH using potentiometric titrations, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) from a liquid microjet. Our results reveal that the identity of the anion has no significant effect on the nanoparticles surface charge density and relative surface potential at bulk pH where silica is negatively charged, consistent with textbook arguments of electrostatics and their exclusion from the region of the electrical double layer that regulates these properties. By contrast, the identity of the cation in solution is significant on both the surface charge density and surface potential. Specific cation effects are rationalized by their respective distance of closest approach to the nanoparticles surface-the hydrated cation diameter sets the outer Helmholtz plane and in turn the capacitance of the Stern layer.

Quantifying electron-transfer in liquid-solid contact electrification and the formation of electric double-layer

“…After the liquid being vaporized, the surface charge densities on the ceramic surfaces were measured by using KPFM at different substrate temperatures. According to previous studies, ions will be produced by ionization reaction on the oxide and nitride surfaces when they contact the aqueous solutions [25][26][27][28][29] . For example, O − ions will be generated by the ionization reaction on the SiO 2 surface as shown below (The hydroxyl on the SiO 2 surface is usually produced by adsorbing water molecules in the air or contacting with water) 29 :…”

The elusive silica/water interface: isolated silanols under water as revealed by vibrational sum frequency spectroscopy

“…Moreover, pH dependent studies show that the pK a of the isolated silanols is higher than 10.5. Finally, the identification of the isolated silanol band opens new opportunities to further understand the mechanism of adsorption of various molecules, including specific ion interactions, [44][45][46][47] on the surface of this commonly used material. , B3400 cm À1 have the same sign (i.e.…”

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

“…The internal void space allows for interrogating liquids in a confined space, and the huge surface area will allow for sensitive probing of solid-liquid interfacial chemistry. While X-ray photoelectron spectroscopy was used to obtain electronic structure information on colloidal silica nanoparticles using liquid jets, [166][167][168] and attosecond XUV streaking from aerosolized silica nanoparticles 169 have been reported in the literature, we propose to extend these studies to use electron angular information to provide a more complete picture on the evolution of water phase changes within the nanoparticle. Not only will we be able to determine the thickness of the shell of silica nanoparticles, we also anticipate that information on chemistry located within the environment of these nanoparticles will become accessible.…”