L. N. Obolenskaya

Synthesis, characterization, and properties of nanoscale titanium dioxide modifications with anatase and η-TiO2 structures

Nanoscale titanium dioxide modifications with anatase and η-TiO2 structures have been obtained by the sulfate method. Bands characteristic of the η-TiO2 phase are selected in the Raman and IR spectra of the samples containing this phase. A study of the properties of synthesized samples applying a complex of physicochemical methods revealed that nanocrystals in the samples containing phases of different modifications differ in size, structure, and surface composition. It is shown that the abovementioned nanoscale modifications are characterized by the efficient sorption of As (V), Bi (III), and V (V) from aqueous media; the degree of sorption depends on the size and structural form of nanocrystals.

Synthesis and morphology of anatase and η-TiO2 nanoparticles

Samples containing anatase and η-TiO2 nanoparticles have been prepared from titanyl sulfate solutions and characterized by X-ray diffraction, transmission electron microscopy, and electron diffraction. Unit-cell parameters of η-TiO2 have been proposed that do not rule out a relationship between the anatase and η-TiO2 structures. The samples containing anatase and η-TiO2 differ in crystallite size and specific surface area and consist of agglomerates of particles of various sizes covered with an amorphous layer. We have studied the effect of synthesis conditions on the ability to prepare a particular titania polymorph with various functional characteristics.

Influence of the conditions of the sulfate method on the characteristics of nanosized anatase-type samples

The nanosized anatase modification of titanium dioxide was prepared from two forms of solvated titanyl sulfate (TiOSO4·2H2O and TiOSO4·xH2SO4·yH2O) at different initial concentrations of the reagent under different conditions of the hydrolysis and coagulation. The sample characteristics (the sizes of aggregates, microparticles, nanoparticles, and coherent scattering regions, the specific surface area, the nano- and ultrananopore volumes) were deter-mined by scanning electron microscopy, small-angle and wide-angle X-ray diffraction, and physical adsorption of nitrogen at −196 °C. The relationship between these characteristics and the conditions of the sample preparation was established. The optimal processing conditions were found for the synthesis of samples with a high practical yield of the anatase-type phase.

Composition, microstructure, and properties of anatase and η-TiO2 nanoparticles

Nanoparticulate anatase and η-TiO2 prepared via a sulfate route have been shown (using powder X-ray diffraction, scanning electron microscopy, X-ray microanalysis, and IR spectroscopy) to differ in micro- and nanoparticle size and elemental composition. The degree of As(V), V(V), and Bi(III) extraction from aqueous solutions (for the last element, a content below its maximum allowable concentration has been reached) using nanoparticulate titania adsorbents depends on their composition, crystal structure, crystallinity, and microstructure. The synthesized anatase and η-TiO2 powders are shown to be potentially attractive carriers of PdCl2-CuCl2/TiO2 catalysts for low-temperature carbon monoxide oxidation in air.

Efficiency of sensitizing nano-titania with organic dyes and peroxo complexes

A new method of sensitizing titania by treatment of the reaction mixture with Methylene Blue, Methyl Red or hydrogen peroxide is developed; the sensitizer was introduced into the reaction mixture while synthesizing nanosize TiO2 from titanyl sulfate. The samples prepared by this method are compared to the samples prepared by cold impregnation of Methylene Blue, Methyl Red or hydrogen peroxide on titania, pre-synthesized by sulfate method, or commercial Degussa P25 and Hombikat UV100. The samples were characterized by X-ray diffraction; their photocatalytic activity was studied in the model reaction of Methyl Orange decomposition in aqueous solution under UV and visible light. The highest photocatalytic activity under visible light was found for titania, sensitized with titanium peroxo complexes by the new method. It is also active for photodegradation of salicylic acid under visible light.

Effect of methylene blue modification on the structural, morphological, and photocatalytic properties of nanosized η-TiO2

The structural and morphological features of samples containing titanium dioxide, obtained by the sulfate method in the presence of methylene blue dye MeB (sample with η-TiO2) and in its absence (sample with anatase), have been determined using a complex of analytical methods. For the sample with η-TiO2, the sizes of titanium dioxide crystallites (5.0(2) nm) are smaller than the nanoparticle sizes (5.5–9.0 nm), which does not exclude their defect structure. This sample exhibited a higher tendency of nanoparticles to agglomeration (the presence of strong bonds between nanoparticles) and a low tendency to aggregation (the presence of weak bonds). It is shown that a MeB-modified sample with η-TiO2 has high photocatalytic activity in the visible spectral range in the model reaction of methyl orange dye decomposition.

Photocatalytic properties of composites containing titania nanoparticles on submicron Y2O3 spheres

The photocatalytic properties of TiO2/Y2O3 composites prepared by coating with anatase and η-TiO2 nanoparticles, Degussa P25, and Hombifine N by simultaneous dispersing Y2O3 and TiO2 powders in a weakly alkaline aqueous medium (procedure I) or Y2O3 powder in an acidic titanium-containing hydrosol (procedure II) have been studied for the first time. The results demonstrate that, after sonication, the η-TiO2/Y2O3 and anatase/Y2O3 composites have almost identical photocatalytic activities (PCAs), which are however lower than those of anatase and η-TiO2, whereas the PCA of the samples prepared by procedure II is comparable to that of nano-TiO2 under UV irradiation and exceeds the activity of Degussa-N,S (Degussa P25 annealed with thiourea) exposed to visible light. The highest PCA is offered by a TiO2〈Cl〉/Y2O3 composite modified with the products of titanium tetrachloride hydrolysis in air.

Nanocomposites based on silicon dioxide of different nature with functional titanium dioxide nanoparticles

Nanocomposites TiO2/SiO2 with photocatalytic and adsorptive properties were prepared by codispersing of η-modification and anatase (commercial Hombifine N) and SiO2 (opal, granules, ultrafine) in ethanol (or ethanol–water mixture in the presence of chlorophylls or porphyrins) with ultrasonic treatments of the mixture (method 1) and an aqueous solution of KOH with a microwave treatment (method 2), as well as the introduction of SiO2 in the reaction mixture during the synthesis of TiO2 by brief hydrolysis of sulfate titanyl (method 3). It was found that the state of titania in the sample (X-ray amorphous or nanocrystalline) and its deposition on SiO2 nanocomposites depend on the method and the conditions of obtaining. It was established that the photocatalytic activity of nanocomposite TiO2/SiO2 (granules) (method 1) photosensitized by coproporphyrin I in the visible range and the photocatalytic activity of nanocomposite TiO2/SiO2 (opal) (method 3) in the near UV range exceed activity of the commercial sample of TiSiO4 by more than 20-fold and ~7-fold, respectively. It was shown that the nanocomposite TiO2/SiO2 (opal) significantly reduces the concentration of cations (in particular, Be, Ni, Bi) in the model water systems.

Conditions for Titania(IV) Recrystallization from the η Modification to Anatase

The effect of some sensitizers (methylene blue, methyl red, chlorophylls, coproporphyrin I, and hydrogen peroxide) on the transformation of η-TiO2, which is an anatase precursor in titanyl sulfate hydrolysis, into anatase has been studied. A decrease in the average crystallite size and suppression of the transformation of η-TiO2 into anatase is observed in the presence of methylene blue and methyl red organic dyes, as well as Ti(IV) peroxocomplexes,. The sample synthesized in the presence of 1 M H2O2 is characterized by the smallest crystallite sizes (2−4 nm) and the highest photocatalytic activity.

Molecular interaction between DNA molecules and nanoscale modifications of titanium dioxide with the structures of anatase and η-TiO2

The interaction of linear DNA molecules (hydrolysis products of Lambda phage DNA) with nanoscale modifications of titanium dioxide with anatase and η-TiO2 structures is studied. The photosensitization of adsorption and degradation processes of DNA under the effects of visible light is revealed. It is established that the anatase exhibits increased activity towards DNA in a low salt buffer, while η-TiO2 has a higher adsorption capacity in a buffer with high ionic strength. Recommendations on the practical application of nanoscale modifications of titanium dioxide with the structures of anatase and η-TiO2 are given.