O. I. Gyrdasova

Synthesis and properties of titanium glycolate Ti(OCH2CH2O)2

A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH2CH2O)2 has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH2CH2O)2 in air gives titanium dioxide as anatase (400–500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500–950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO2−xCx phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiOx(OCH2CH2O)2−2x(OH)2x·xH2O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology.

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 and structure of quasi-one-dimensional zinc oxide doped with manganese

Nanotubes of manganese-doped zinc oxide Zn1 − xMnxO (0 ≤ x ≤ 0.2) were synthesized by heating the Zn1 − xMnx(HCOO)(OCH2CH2O)1/2 precursor in air at 500°C. The precursor with extended crystals was synthesized by a solvothermal method based on heat treatment of a mixture of Zn1 − xMnx(HCOO)2 · 2H2O with an ethylene glycol excess at 100–130°C. The tubular morphology of Zn1 − xMnxO particles was identified by transmission electron microscopy. Tubular quasi-one-dimensional particles were shown to have a nanodispersed polycrystalline structure, the size of separate crystallites being from 5 to 20 nm. X-ray photoelectron spectroscopy suggested that the manganese distribution on the outer surface layer of Zn1 − xMnxO nanotubes is nonuniform.

Optical and Photocatalytic Properties of Carbon-Activated Anatase with Spherical Shape of Aggregates

Carbon-doped anatase with spherical shape of aggregates has been synthesized by the developed precursor technique with the use of Ti(OCH2CH2)2 as a precursor. The synthesized samples of the general composition TiO2−yCy:nC with different carbon content have been tested for the photocatalytic activity in the oxidation reaction of water-dissolved hydroquinone during irradiation in ultraviolet and visible light. It was shown that the optical and photocatalytic properties of TiO2−yCy:nC depend strongly on the concentration of carbon. The first-principles calculations of the electronic band structure and optical absorption spectra have been carried out. The probabilities of formation of carbon for oxygen substitutional defects and interstitial defects (implantation of carbon atoms into interstitial sites) have been analyzed. The calculations performed allowed us to determine the dominating type of defects responsible for absorption and photocatalytic activity of carbon-doped anatase in the visible spectral region.Graphical Abstract

Nature of defects in nanocrystalline zinc oxide with particles of tubular morphology

Nanostructured ZnO powders with particles of tubular form were synthesized by a precursor method. A narrow symmetrical line with a g factor of 2.002 was detected in the ESR spectra of the materials. On the basis of analysis of the dependence of the line intensities on the heat treatment conditions it was concluded that the signal belongs to singly charged oxygen vacancies VO+.

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].