ISSN 1063-7745, Crystallography Reports, 2014, Vol. 59, No. 3, pp. 430–436. © Pleiades Publishing, Inc., 2014. Original Russian Text © P.A. Demina, A.M. Zybinskii, G.M. Kuz’micheva, L.N. Obolenskaya, E.V. Savinkina, N.A. Prokudina, 2014, published in Kristallografiya, 2014, Vol. 59, No. 3, pp. 477–483. 430 INTRODUCTION Currently, the purification, conservation, and regeneration of water resources are urgent problems. This concerns all types of aqueous systems, including natural, domestic, and industrial. In recent years, requirements for drinking-water quality have become more stringent. Inorganic adsorbents such as Al 2 O 3 , SiO 2 , ZrO 2 , and TiO 2 are characterized by better mechanical properties and higher thermal stability than other biosorbents and organic sorbents. Among inorganic sorbents, nanoscale titanium dioxide modi- fications with anatase, rutile, brookite, and η-TiO 2 structures hold a particular place [1]. All modifica- tions have a high ability of absorbing As(III) and As(V), independent of the formal charge (rutile, broo- kite, anatase, or η-TiO 2 ) [1–3]; U(VI) (rutile) [2]; and Bi (V) (anatase) [4] from aqueous media and a favor- able adsorption kinetics for extracting other insoluble metals present in aqueous systems in low concentra- tions (Cu(II) [5], As(V) [6–8], V(V) [9], Cu(II) and Mn(II) [10], and Cd(II) [11]). These properties ensure rapid purification from heavy metals and/or facilitate the reduction of their concentration to a few micrograms per liter. The adsorption capacity is known to depend on the surface properties: chemical composition, physical state, porosity, and specific surface. The unique adsorption properties of nanoscale titanium dioxide modifications are attributed to the formation of sur- face hydroxyl groups with high activity at a crystallite size (in this case, the crystallite size is equal to the coherent scattering region) reduced to 100 Å or smaller; it is of fundamental importance that the num- ber of such crystallites must be close to 100% [1, 2]. These groups are self-generated when contacting water due to the quantum-size effect on wide-gap tita- nium dioxide semiconductors (3.2 eV for anatase, 3.0 eV for rutile, and above 3.25 eV for brookite). It can be increased, for example, by 0.15 eV or more for anatase at a crystallite size of 30–40 Å [1, 2]. In other words, when the size of a titanium dioxide crystallite decreases to a few nanometers, the physicochemical behavior of surface atoms changes strongly due to the variation in the ratio of the numbers of surface and inner atoms, which is much larger in very small crys- tallites than in micrometer-sized crystals. Note that the properties of atoms on the crystallite surface differ significantly from those of large crystals: the oxygen atoms in crystallites that are adjacent to surface tita- nium atoms are transformed to highly active hydroxyl groups when contacting water; thus, the adsorption properties of crystallites are much better than those of large crystals. As was shown in [1, 2], the adsorption properties of one large crystal are much worse than those of several small crystallites with the same total surface. It was suggested in [1] that the generation of surface hydroxyl groups results from the photodecom- position of water molecules by nanosized semicon- ductors (by nano-TiO 2 in the case under consider- ation). Important factors affecting the sorption of metals is the composition of the liquid solution phase from which analytes are extracted (pH, ionic force, and the nature and concentration of analytes) and the sorption con- ditions (temperature, contact time, adsorbent mass, etc.). The studies on the extraction of analytes onto NANOMATERIALS, CERAMICS Adsorption Ability of Samples with Nanoscale Anatase to Extract Nb(V) and Ta(V) Ions from Aqueous Media P. A. Demina a , A. M. Zybinskii a , G. M. Kuz’micheva a , L. N. Obolenskaya a , E. V. Savinkina a , and N. A. Prokudina b a Moscow State University of Fine Chemical Technology, pr. Verndaskogo 86, Moscow, 119571 Russia b Aspect Association, pr. Vernadskogo 86, Moscow, Russia e-mail: galina_kuzmicheva@list.ru Received June 6, 2013 Abstract—The adsorption ability of titanium dioxide samples with nanoscale anatase prepared by the sulfate method and Degussa (Evonik) P25, Hombfine N, and Hombikate UV-100 commercial agents with different compositions and characteristics to extract Nb(V) and Ta(V) ions from a model aqueous system has been investigated for the first time. It is established that the degree of sorption R (%) depends on the sorption con- ditions and the nature of analyte. It is demonstrated that the degree of sorption of Nb(V) ions in the presence of all samples is the highest (R max = 99.9%) for Degussa P25, except for the peroxide-modified samples on which the maximum sorption of Ta(V) ions with R max = 99.9% has been attained. DOI: 10.1134/S1063774514030079