Аdsorption of zinc (II) on silica and alumina-silica surfaces: results of experiment and simulation

Studying interaction of zinc (II) with silica and alumina-silica surfaces is important for several reasons. From a practical point of view, it is carried out in the framework of the creation of a medicinal product, the ingredients of which are, in particular, silica(alumina)containing sorbent and zinc compound; from a theoretical point of view, it is a search for the adsorption patterns on the mentioned surfaces in a series of d-elements with a close electronic structure (zinc, copper, nickel, cadmium, etc.). In addition, it is advisable to supplement the experimental adsorption data with the results of quantum chemical simulation of the structure and formation energy of zinc (II) complexes with active surface centers. Adsorption of Zn 2+ ions from a neutral aqueous solution on silica and alumina-silica materials was studied by means of the method of adsorption isotherm. The specific surface of the materials was determined by method of thermal desorption of argon. Quantum chemical analysis of the structure and energy of formation of the hydrated zinc sulfate ion pair on silica and alumina-silica surfaces was performed by means of Hartree-Fock-Roothaan method with extended basis set 6‑31++G(d,p).  According to the magnitude of adsorption (A) of zinc, the test materials are divided into three groups: 1) enterosgel, kaolin, nanosilica A-300 and polymethylsiloxane, for which А max is from 0.15 to 0.3 mg/g; 2) Syloid® 244 FP, KG-60 and KG-40, aminopropylaerosil, smectite (А max  from 1.2 to 12.0 mg/g); 3) zeolites NaA-TK-1173 and NaX (А max more than 30 mg/g). It is concluded that the high adsorption activity of zinc(II) is primarily due to the presence of developed porous structure. The most probable places of interaction between hydrated zinc ions and hydroxyl group of silica and alumina-silica surfaces are determined by means of quantum chemical simulation. The pK Me values have been calculated of ion exchange of silica surface when interacting with Zn 2+ cations.