Ion–ion correlation, solvent excluded volume and pH effects on physicochemical properties of spherical oxide nanoparticles

• Published in: Journal of colloid and interface science Vol. 462; pp. 325 - 333
• Main Authors: Ovanesyan, Zaven, Aljzmi, Amal, Almusaynid, Manal, Khan, Asrar, Valderrama, Esteban, Nash, Kelly L., Marucho, Marcelo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.01.2016
• Subjects: Chemistry, Physical; Density functional theory; Electrolytes - chemistry; Hydrogen-Ion Concentration; Ions - chemistry; Nanoparticles; Nanoparticles - chemistry; Particle Size; Quantum Theory; Silicon Dioxide - chemistry; Solvents - chemistry; Surface charge density; Surface chemistry; Surface Properties; Zeta potential; Nanoparticles; Surface charge density; Density functional theory; Zeta potential; Surface chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2015.10.019

The comparison between conventional mean field Poisson–Boltzmann Theory (Fig. a) and the proposed classical solvation density functional theory (Fig. b) reveals that water crowding and ion correlation effects play an important role in the physicochemical properties of spherical silica nanoparticle. [Display omitted] One major source of complexity in the implementation of nanoparticles in aqueous electrolytes arises from the strong influence that biological environments has on their physicochemical properties. A key parameter for understanding the molecular mechanisms governing the physicochemical properties of nanoparticles is the formation of the surface charge density. In this article, we present an efficient and accurate approach that combines a recently introduced classical solvation density functional theory for spherical electrical double layers with a surface complexation model to account for ion–ion correlation and excluded volume effects on the surface titration of spherical nanoparticles. We apply the proposed computational approach to account for the charge-regulated mechanisms on the surface chemistry of spherical silica (SiO2) nanoparticles. We analyze the effects of the nanoparticle size, as well as pH level and electrolyte concentration of the aqueous solution on the nanoparticle’s surface charge density and Zeta potential. We validate our predictions for 580Å and 200Å nanoparticles immersed in acid, neutral and alkaline mono-valent aqueous electrolyte solutions against experimental data. Our results on mono-valent electrolyte show that the excluded volume and ion–ion correlations contribute significantly to the surface charge density and Zeta potential of the nanoparticle at high electrolyte concentration and pH levels, where the solvent crowding effects and electrostatic screening have shown a profound influence on the protonation/deprotonation reactions at the liquid/solute interface. The success of this approach in describing physicochemical properties of silica nanoparticles supports its broader application to study other spherical metal oxide nanoparticles.