V. N. Krasilnikov

Structural, Optical, and Photocatalytic Properties of Quasi-One-Dimensional Nanocrystalline ZnO, ZnOC:nC Composites, and C-doped ZnO

Various thermolysis rotes of zinc glicolate complexes are considered for the synthesis of quasi-one-dimensional nanostructured aggregates ZnO and Zn–O–C used as photocatalysts. Structural features of quasi-one-dimensional aggregates Zn–O–C and ZnO are investigated in detail. Transmission electron microscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy methods demonstrate that the aggregates Zn–O–C have either composite structure (ZnO crystallites in amorphous carbon matrix) or a C-doped ZnO single-phase structure depending on heat treatment conditions, and that all the aggregates exhibit as a rule a tubular morphology, a nanocrystalline structure with a high specific surface area, and a high concentration of singly charged oxygen vacancies. The mechanism of the nanocrystalline structure formation is discussed and the effect of thermolysis condition on the formation of the textured structure of aggregates is investigated. The results of examination of the photocatalytic and optical absorption properties of the synthesized aggregates are presented. The photocatalytic activity for the hydroquinone oxidation reaction under ultraviolet and visible light increases in the series: the reference ZnO powder, quasi-one-dimensional ZnO, quasi-one-dimensional aggregates C-doped ZnO, and this tendency correlates with the reduction of the optical gap width. As a result of our studies, we have arrived at an important conclusion that thermal treatment of ZnO:nC composites allows a C-doped ZnO with high catalytic activity. This increasing photoactivity of C-doped ZnO aggregates is attributed to the optimal specific surface area and electron-energy spectrum restructuring to be produced owing to the presence of singly charged oxygen vacancies and carbon dissolved in the ZnO lattice.

Synthesis, crystal structure and optical properties of Me(OH)(HCOO)2 (Me = Al, Ga)

The formation conditions, crystal structure and luminescence properties of aluminum and gallium hydroxide diformates, Me(OH)(HCOO)2, have been established. Both compounds crystallize in a monoclinic lattice (space group C2, #5 and Z = 8) with parameters: a = 8.8629(2) A, b = 9.9890(2) A, c = 10.2411(1) A, β = 106.223(1)°, and V = 870.56(3) A3 (Al) and a = 8.8746(1) A, b = 10.3291(1) A, c = 10.27870(9) A, β = 105.7565(6)°, and V = 906.81(2) A3 (Ga). The emission spectra of Me(OH)(HCOO)2 under UV excitation with wavelength λ = 285 nm exhibit maxima in the range of 440–470 nm. The emission accompanied by light-blue luminescence is greatly enhanced when going from the aluminum to the gallium compound. The origin of intrinsic emission centers responsible for the luminescence properties of Me(OH)(HCOO)2 is suggested and the higher emission of the gallium hydroxide diformate is substantiated by means of density-functional theory calculations.

Optical properties, emission characteristics, and photocatalytic activity of nanosize titanium dioxide doped with europium

Nanosized solid solutions Ti1 − xEuxO2 − x/2 (x = 0.05, 0.1, 0.15) with a high specific surface area have been produced by the original precursor method using glycolate of the composition Ti1 − xEux(OCH2CH2O)2 − x/2 as a precursor. The structural properties of the synthesized solid solutions have been examined by electron microscopy and Raman spectroscopy methods. The effect of temperature and concentration of dopant in the solid solutions on the anatase-rutile phase transition has been studied. The emission characteristics of Eu3+ luminescence centers in titanium dioxide are presented. An essential shift in the optical absorption edge to the ultraviolet region has been registered for the composition Ti0.9Eu0.1O1.95, which is due to the size factor. It was established that these solid solutions can serve as photocatalysts in ultraviolet and visible radiation and their photocatalytic activity increases with the dopant concentration.

CRYSTAL STRUCTURE AND VIBRATIONAL SPECTRA OF M[VO(2)(SeO(4))(H(2)O)(2)]center dot H(2)O (M = K, Rb, NH(4))

By the hydration of MVO(SeO4)2 with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition M[VO2(SeO4)(H2O)2]·H2O (K, Rb, NH4) are synthesized and their physicochemical properties are studied. Based on the X-ray and neutron diffraction data, it is found that their crystal structure is composed of VO6 octahedra linked in infinite chains by bridging SeO4 tetrahedra. Each of the VO6 octahedra has two short terminal V-O bonds forming a bent dioxovanadium group VO2+. Two water molecules are coordinated by vanadium and one molecule is out of the first coordination sphere in the interchain space. The vibrational spectra of the studied compounds are completely consistent with their structural features.