I. V. Baklanova

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+.

Crystal structure and optical properties of germanates Ln2Ca(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y)

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln2Ga(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.

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.

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.

Electronic band structure, optical absorption, and photocatalytic activity of iron-doped anatase

Quasi-one-dimensional solid solutions of the composition Ti1 − xFexO2 − x/2 (0.005 ≤ x ≤ 0.050) with the anatase-type structure and extended aggregates have been prepared by the precursor method. The absorption spectra of the solid solutions have been investigated in the ultraviolet and visible regions, and the photocatalytic activity in the oxidation reaction of hydroquinone in water has been estimated. It has been found that the synthesized solid solutions serve as photocatalysts only under ultraviolet irradiation, and their photoactivity increases with an increase in the dopant concentration. The first-principles calculations of the electronic band structure and optical absorption in iron-doped anatase and rutile have been performed using the pseudopotential method LSDA + U (with the VASP software package). The on-site exchange-correlation parameters have been calibrated in the calculations of the electronic band structure of hematite α-Fe2O3 and ilmenite FeTiO3. It has been shown that, despite the appearance of impurity states within the band gap of anatase and rutile, doping with iron does not cause substantial absorption in the visible region, which correlates with the increase in photocatalytic activity only under ultraviolet irradiation. The most probable cause of the experimentally observed absorption in the visible region is the presence of finely dispersed hematite impurities in the obtained samples.

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

Synthesis, structure, and properties of V2O3(XO4)2 (X = S, Se)

Compounds described as V2O3(XO4)2, where X = S or Se, were prepared from vanadium(V) oxide mixtures with concentrated sulfuric and selenic acids. The physicochemical properties of the products were studied; for V2O3(SeO4)2, the crystal structure was determined by powder X-ray diffraction and neutron diffraction, and its key differences from the structure of V2O3(SO4)2 were identified. V2O3(SeO4)2 crystallizes in the monoclinic system with the unit cell parameters a = 15.3831(2)Å, b = 5.54096(5)Å, c = 9.71644(7)Å, β = 111.886(1)°, V = 768.51Å3, space group C2/c (no. 15).

Synthesis and vibrational spectra of solid solutions based on lanthanum gallate

The synthesis conditions for single-phase solid solutions based on lanthanum gallate, LaGa1 − xMgxO3 − δ(x= 0–0.25, solid-phase method) and La1 − ySryGa1 − yMgyO3 − δ(y= 0–0.2, glycine nitrate method), have been investigated. The structural parameters have been calculated using X-ray powder diffraction data. The IR and Raman spectra have been analyzed. Regularities in the changes in the structural parameters and vibrational spectra with composition are established.

Synthesis, structure and spectroscopic characteristics of Ti(O,C)2/carbon nanostructured globules with visible light photocatalytic activity

A morphology-controlled facile synthesis of titanium-glycolate precursors with subsequent annealing in He and air atmospheres has been exploited for the production of nanostructured composite globules, whiskers and plates of C-modified titanium dioxide. Characterisation tests proved the as-obtained globule composites to exclusively exhibit high-specific surface area (up to 150–170 m2 g−1), thus being useful for photocatalytic applications in the visible-light region. The combination of the electron paramagnetic resonance, X-ray photoelectron spectroscopy, absorption spectroscopy and transmission electron microscopy revealed the presence of three kinds of carbon in the globules: a small bandgap (with measured width of 0.8 eV) amorphous carbon surrounding the anatase nanocrystallites, C-containing radicals including carbonates on the surface of TiO2 and interstitial carbon in the oxygen position of the TiO2 lattice. It was found that the maximum visible-light photocatalytic activity of the globules is determined by the optimal surface concentration of amorphous carbon of about 0.002 wt.% m−2. Under these conditions, the highest synergic photosensitising effect on TiO2 nanocrystallites of all three kinds of carbon is expected.

Observation of ferromagnetism at room temperature in polycrystalline Zn1 − x Fe x O solid solutions synthesized by the precursor method

Polycrystalline Zn1 − xFexO (0 ≤ x ≤ 0.075) solid solutions with the wurtzite structure, which belong to the class of diluted magnetic semiconductors, have been synthesized by the precursor method using a mixed formate of the composition Zn1 − xFex(HCOO)2 · 2H2O as a precursor. It has been found that the iron concentration in Zn1 − xFexO solid solutions, which exhibit ferromagnetic properties with a high degree of magnetization at room temperature, is determined by two factors: (1) the degree of substitution of iron for zinc in the structure of zinc formate Zn(HCOO)2 · 2H2O and, therefore, in the structure of zinc oxide ZnO and (2) the conditions of heat treatment of the precursor. It has been shown using samples with x = 0.025 and 0.05 as an example that the magnetization of Zn1 − xFexO solid solutions regularly increases with an increase in the iron concentration. Based on the results of the X-ray photoelectron spectroscopy analysis of Zn1 − xFexO powders, it has been suggested that the iron concentration increases in the surface layer of particles, and the oxidation state of iron is 3+.