M. Yu. Yanchenko

Electronic structure and the optical and photocatalytic properties of anatase doped with vanadium and carbon

The electronic structures of undoped anatase and anatase doped with carbon and vanadium have been calculated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the LSDA + U approximation. It has been shown that the doping of TiO2 leads to the formation of narrow bands of the C and Vimpurity states in the band gap. The calculations of the imaginary part of the dielectric function have made it possible to estimate the intensity of the optical absorption. It has been established that the doping with vanadium and carbon leads to optical absorption in the visible range and to an increase in the absorption in the ultraviolet range up to 4 eV. This should result in an increase in the photocatalytic activity on the surface of the doped anatase. The experimental determination of the photocatalytic activity of whiskers of the anatase doped with carbon and vanadium in the reaction of hydroquinone oxidation has confirmed the increase in the activity of the doped materials under exposure to ultraviolet, visible, and blue light. The phenomenon of dark catalysis in the anatase doped with carbon and vanadium has been interpreted within the concept of low-energy electronic excitatio ns between the impurity levels of carbon.

Effect of Doping with 3d Elements (Co, Ni, Cu) on the Intrinsic Defect Structure and Photocatalytic Properties of Nanostructured ZnO with Tubular Morphology of Aggregates

The precursor-derived nanostructured solid solutions Zn0.95M0.05O (M = Co, Ni, Cu) with tubular aggregates have been investigated using optical absorption spectroscopy and electron paramagnetic resonance. The dependences of the concentration of intrinsic defects Vo+ and the effective band gap on the dopant type have been determined. It has been shown using the oxidation reaction of hydroquinone dissolved in water as an example that an increase in the photocatalytic activity in the series ZnO → Zn0.95Ni0.05O → Zn0.95Co0.05O Zn0.95Cu0.05O in the ultraviolet and visible spectral regions correlates with a decrease in the band gap and with an increase in the concentration of oxygen vacancies VO+.

Synthesis and photocatalytic activity of Ti[1 − x]VxO[2 − y]Cy whiskers in hydroquinone oxidation in aqueous solutions

Ti1−xVxO2−yCy (0 ≤ x ≤ 0.10 and x = 0.50) whiskers having the anatase structure were synthesized via thermolysis of vanadium-doped titanium glycolate of composition Ti1−xVx(OCH2CH2O)2 (0 ≤ x ≤ 0.10 and x = 0.50). The starting reagents used to prepare Ti1−xVx(OCH2CH2O)2 were mixtures of coprecipitated titanium and vanadyl hydroxides, which were heated in ethylene glycol at T ≤ 200°C: (1 − x)TiO(OH)2 + xVO(OH)2 + 2HOCH2CH2OH = Ti1−xVx(OCH2CH2O)2 + 3H2O↑. Thermolysis of vanadium-doped titanium glycolate in various gas media over a wide range of temperatures is useful to prepare titania samples doped with both vanadium and carbon to form a phase of the general composition Ti1 − xVxO2 − yCy whiskers prepared by thermolyzing Ti1 − xVx(OCH2CH2O)2 in air at 450°C were found to have a high photocatalytic activity in hydroquinone oxidation in aqueous solutions irradiated in the UV spectral range; the photocatalyst’s activity increases with increasing vanadium concentration. When hydroquinone was irradiated in the blue, the maximal catalytic activity was discovered in a sample of composition Ti0.50V0.50O2−yCy. Quantum-chemical calculations support experimental data that the double doping of titania (Ti1−xVxO2−yCy) enhances its photocatalytic activity compared to undoped anatase or anatase doped in one sublattice: Ti1−xVxO2 and TiO2−yCy.

Synthesis, optical properties, and photocatalytic activity of lanthanide-doped anatase

Quasi-one-dimensional (1D) Ti1 − xLnxO2 − x/2 anatase solid solutions were prepared by heating Ti1 − xLnx(OCH2CH2O)2 − x/2 precursors, where Ln = Nd, Eu, Tb, Er (x = 0.025), or Sm (0.005 ≤ x ≤ 0.025), in air. These solid solution were found to have a photocatalytic activity in hydroquinone oxidation in aqueous solution under exposure to UV radiation. UV-Vis absorption spectra were recorded for Ti1 − xLnxO2 − x/2 (Nd, Sm, Eu, Tb, or Er). The electronic structure and optical absorption spectra were calculated for anatase doped with neodymium, samarium, or terbium.

Synthesis and photocatalytic properties of low-dimensional cobalt-doped zinc oxide with different crystal shapes

The glycoxide complexes Zn1–xCox(HCOO)(HOCH2CH2O)1/2 and Zn1−xCox(OCH2CH2O) (0 ≤ x ≤ 0.3) have been synthesized by heating ethylene glycol solutions of zinc formate Zn(HCOO)2 · 2H2O or its mixtures with cobalt formate Co(HCOO)2 · 2H2O. The crystals of these complexes have the shape of filaments (needles, bars) and distorted octahedra, respectively. A new method in which these complexes are used as the precursor is suggested for the synthesis of low-dimensional wurtzite-like Zn1−xCoxO. The shape of the precursor crystals is fully inherited by Zn1−xCoxO resulting from their heat treatment. The Zn1−xCoxO solid solutions show high photocatalytic activity in hydroquinone oxidation in aqueous solution under UV or blue light irradiation, and their activity increases as their cobalt content is increased.

Glycolate Ti1 − xFex(OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − xFexO2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti1 − xFex(OCH2CH2O)2 − x/2 (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti1 − xFex(OCH2CH2O)2 − x/2 in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti3Fe2(OCH2CH2O)9 were described. It was found that the synthesized Ti1 − xFexO2 − 2x/2 solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti1 − xFexO(2 − x/2) − yCy) and also composites on its basis, which contain an excess amount of carbon, was proposed.

Synthesis, microstructure, and native defects of photoactive Zn 1 − x Cu x O solid solutions (0 ≤ x ≤ 0.1) with tubular aggregates

258 Design of photocatalysts based on nanosized zinc oxide for oxidation of toxic and colored organic com pounds has been a perspective direction of research in recent years [1–3]. The efficiency of such materials is determined by their composition, size, and aggregate morphology and microstructure, as well as by the existence of native structural defects. In particular, doping of ZnO with 3d metals or formation of particles of extended shape causes a considerable enhancement of the photocatalytic activity of zinc oxide and often leads to the shift of the catalytic process from the char acteristic UV to the visible spectrum [4, 7]. To fabri cate photocatalysts with enhanced functional charac teristics being active under visible light, we synthesized the Zn1 – xMxO solid solutions (M = Co, Mn, Fe, Ni) with tubular morphology of aggregates [5, 8].

Spectroscopic and voltammetric characteristics of α-Zn 2 SiO 4 :V luminophor

Single-phase luminophor Zn2SiO4:V with willemite structure is prepared by hydrothermal method. It is found that the Zn: Si: V ratio between cations is 2: 0.9: 0.1. It is shown that the inclusion of vanadium in the willemite structure reduces the width of the bandgap by ΔEg ≈ 2 eV. Using a combination of spectroscopic and voltammetric techniques, it is found the zinc silicate matrix contains vanadium ions with charge states V5+, V4+, and V3+. In addition, magnetic ions form clusters.

Synthesis and properties of M2V8O21 (M = K, Tl) octavanadates and K2−xTlxV8O21 (0 ≤ x ≤ 2) solid solutions

Formation parameters and properties of M2V8O21 octavanadates where M = K and Tl were studied using X-ray powder diffraction, microscopy, thermogravimetry, vibrational spectroscopy, EPR, and voltammetry. Original synthesis processes for these compounds were developed; their thermal stability parameters were determined. Potassium and thallium(I) octavanadates were shown to form complete solid solutions with each other. Potassium octavanadate in air is stable to 450°C; above this temperature, it transforms, on account of partial reduction of vanadium, to vanadium bronze by the reaction K2V8O21 ↔ K2V8O20.8 + 0.1O2. The K2V8O20.8 percentage in the sample increases with rising temperature. The substitution of small thallium amounts for potassium (x ≥ 0.025) enhances the stability of the phase until it melts at ∼525°C.

Structure and Catalytic Properties of a Cu2+-Containing Hydrogel of Zirconium Dioxide

The distribution of Cu2+ ions in ZrO2 and sulfated ZrO2 hydrogel phases was studied by EPR spectroscopy and voltammetry. The formation of the following three types of copper structures was observed: mononuclear Cu2+ complexes (A), magnetic associates (B), and Cu2+ compounds (C) that gave no EPR signals under the conditions used in the spectroscopic measurements. The specific catalytic activity of various Cu2+ compounds in the liquid-phase reaction of 2,3,5-trimethyl-1,4-hydroquinone oxidation was determined. The copper complexes C were found to exhibit the highest catalytic activity.