Galina M. Kuzmicheva

On the nature of the phase “η-TiO2”

Conditions for a sulfate method for the synthesis of a metastable modification, which has been previously described as “η-TiO2” (Dadachov, 2006), were found and the stability region of this phase in the hydrolysis temperature–hydrolysis duration coordinates was determined. Investigation by a number of methods (X-ray powder diffraction, a differential dissolution method, thermogravimetry, IR spectroscopy, Raman spectroscopy) showed that the η-phase is not a polymorph of TiO2 but is a pseudo-polymorph of titanium dioxide hydrate. It was demonstrated that nanoparticles of the low-temperature η-phase consist of the [TiO2−x·mH2O] core, the structure of which can be described as a superstructure in relation to anatase, and an amorphous shell containing TiO2−x (trace amount), OH, HSO4 and water. The average crystallite size depends on the ratio of the constituents.

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.

Introduction of peroxo groups into titania: preparation, characterization and properties of the new peroxo-containing phase

A new phase, where peroxo groups are incorporated into titania particles, along with anatase and hydrated η-TiO2 with peroxo groups on the surface of titania nanoparticles were prepared by introduction of H2O2 into reaction mixtures while synthesizing TiO2 from TiOSO4 or by cold impregnation of pre-synthesized TiO2. The samples were studied by a range of methods (classical and synchrotron-radiation X-ray powder diffraction, small-angle X-ray scattering, high-resolution scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray absorption spectroscopy, IR and Raman spectroscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance and absorption spectroscopy, DSC). The [TiOx(O2)2−x(H2O)m] phase was first structurally characterized and compared to η-TiO2. Most samples of H2O2-sensitized TiO2 discolor methyl orange under visible light irradiation faster than commercial Hombikat UV100 treated with H2O2. The activity of the samples strongly relating to their phase composition was associated with the existence of a large amount of titanium peroxo complexes along with formation of mixed-phase samples.

KH2PO4 single crystals activated with the Ti4+ ions in the form of TiO2−x × nH2O nanoparticles: Structural peculiarities, point defects, and dielectric properties

Potassium dihydrogen phosphate KH2PO4 (KDP) single crystals activated with Ti4+ ions in the form of TiO2−x × nH2O nanoparticles in the η-phase, synthesized by the sulfate method using TiOSO4 × хH2SO4 × yH2O, have been first grown by the temperature lowering method and cut from pyramidal (P) and prismatic (Pr) growth sectors. The first-performed neutron powder diffraction investigation of P and Pr samples cut from the KDP:Ti4+ crystal allowed us to reveal vacancies in the K and H sites for both samples, their number being larger in the Pr structure compared to the P one. Taking into account the deficiency of the K and H sites, full occupation of the O site, presence of Ti4+ ions in the structure, and the electroneutrality condition, a partial substitution of (PO4)3− anion by the (SO4)2− one, larger for the Pr sample, was observed. The real compositions of P and Pr samples, correlated with the cation-anion internuclear distances, were refined. The dielectric permittivity of the Pr sample was significantly l...

Preparation, physicochemical properties and antimicrobial activity of η-modification of titanium(IV) oxide intercalated with poly( N -vinylcaprolactam)

PVCL-intercalated samples containing nano-dimensional phases with η-modification of the TiO2−x·nH2O composition are obtained by hydrolysis of TiOSO4·xH2SO4·yH2O or TiOSO4·xH2O in the presence of poly(N-vinylcaprolactam) (PVCL). The incorporation of PVCL with water molecules into the interlayer space of the structure of the η-phase—TiO2−x·(PVCL nH2O)—is established by the X-ray diffraction study while the presence of PVCL in the sample composition is confirmed by the X-ray photoelectron and IR spectroscopy CHNS analysis and X-ray spectral microanalysis. Intercalated samples manifest the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. It is shown that the sample composition (the content of hydrated titanium dioxide) the composition of the η-phase (the presence of PVCL and H2O or the water content in the interlayer space of the structure), and the surface composition (S in the form of SO42− groups O in the form of adsorbed water and OH groups) affect the antimicrobial activity in the dark.