Interaction of surface-modified silica nanoparticles with clay minerals

In this study, the adsorption of 5-nm silica nanoparticles onto montmorillonite and illite is investigated. The effect of surface functionalization was evaluated for four different surfaces: unmodified, surface-modified with anionic (sulfonate), cationic (quaternary ammonium (quat)), and nonionic (polyethylene glycol (PEG)) surfactant. We employed ultraviolet-visible spectroscopy to determine the concentration of adsorbed nanoparticles in conditions that are likely to be found in subsurface reservoir environments. PEG-coated and quat/ PEG-coated silica nanoparticles were found to significantly adsorb onto the clay surfaces, and the effects of electrolyte type (NaCl, KCl) and concentration, nanoparticle concentration, pH, temperature, and clay type on PEG-coated nanoparticle adsorption were studied. The type and concentration of electrolytes were found to influence the degree of adsorption, suggesting a relationship between the interlayer spacing of the clay and the adsorption ability of the nanoparticles. Under the experimental conditions reported in this paper, the isotherms for nanoparticle adsorption onto montmorillonite at 25 degrees C indicate that adsorption occurs less readily as the nanoparticle concentration increases.