Kravchenko A. Theoretical simulation of interaction of surface nanoparticular silica with aqueous solution of electrolytes

The equilibrium spatial structures have been found of respective adsorption complexes as well as those of the activated complexes formed due to transitions between the molecular states and charge-separated ones what gives an opportunity to evaluate the deprotonation energy values for surface silanol groups taking into account not only the energy necessary to rupture a Si-OH bond but also the proton hydration one. It has been shown within the frameworks of the model developed that adsorption of cations on silica surface seems to occur preferably on deprotonated silanol groups due to ion exchange. This is accompanied by changes in the protolytic equilibrium of surface groups. The results of calculations testify the formation of a cationic form of silanol group due to contact of silica surface with acidic medium. Relative deprotonation constant is determined by the anion nature and its absolute value increases with an increase in its radius. The model proposed gives a possibility to evaluate the value of zero charge point for silica surface provided it bears adsorption complexes of various nature. Within the frameworks of generalized model for hydrated adsorption complexes of alkali metal compounds in the molecular states and in charge-separated ones involving water molecules and silanol groups of silica surface the pKMe values have been calculated that increase in a row Li<Na<K, what agrees with experimental data. rption on fumed silica corresponds to four-step model, and the pH-dependence of adsorption is determined by the contribution of electrostatic and hydrophobic interactions of BMPA molecules with the sorbent surface. Quercetin and rutin are adsorbed on the fumed silica from organized solutions much more effectively than from aqueous solutions due to the formation of supramolecular complexes (in solution or on the surface), and the pH-dependence of flavonoid adsorption in the composition of these complexes is determined by the sorption properties of individual PVP, HSA and BMPA.