Preparation of hydrophobic SiO<Subscript>2</Subscript>@(TiO<Subscript>2</Subscript>/MoS<Subscript>2</Subscript>) composite film and its self-cleaning properties

TiO₂/MoS₂ composite was encapsulated by hydrophobic SiO₂ nanoparticles using a sol–gel hydrothermal method with methyltriethoxysilane (MTES), titanium tetrachloride (TiCl₄), and molybdenum disulfide (MoS₂) as raw materials. Then, a novel dual functional composite film with hydrophobicity and photocatalytic activity was fabricated on a glass substrates via the combination of polydimethylsiloxane adhesives and hydrophobic SiO₂@(TiO₂/MoS₂) composite particles. The influence of the mole ratios of MTES to TiO₂/MoS₂ (M:T) on the wettability and photocatalytic activity of the composite film was discussed. The surface morphology, chemical compositions, and hydrophobicity of the composite film on the glass substrate were investigated by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle (water CA) measurements. The results indicated that the composite film exhibited stable superhydrophobicity and excellent photocatalytic activity for degradation of methyl orange (MO) even after five continuous cycles of photocatalytic reaction when M/T was 7:1. The water CA and degradation efficiency for MO remained at 154° and 94%, respectively. Further, the composite film showed a good non-sticking characteristic with the water sliding angle (SA) at about 4°. The SiO₂@(TiO₂/MoS₂) composite consisting of hydrophobic SiO₂ nanoparticles and TiO₂/MoS₂ heterostructure could provide synergistic effects for maintaining long-term self-cleaning performance.     

Increases in solar conversion efficiencies of the ZrO<Subscript>2</Subscript> nanofiber-doped TiO<Subscript>2</Subscript> photoelectrode for dye-sensitized solar cells

In this paper, in order to improve the efficiency of dye-sensitized solar cells, we introduced zirconia [ZrO₂] nanofibers into a mesoporous titania [TiO₂] photoelectrode. The photoelectrode consists of a few weight percent of ZrO₂ nanofibers and a mesoporous TiO₂ powder. The mixed ZrO₂ nanofibers and the mesoporous TiO₂ powder possessed a larger surface area than the corresponding mesoporous TiO₂ powder. The optimum ratio of the ZrO₂ nanofiber was 5 wt.%. The 5 wt.% ZrO₂-mixed device could get a short-circuit photocurrent density of 15.9 mA/cm², an open-circuit photovoltage of 0.69 V, a fill factor of 0.60, and a light-to-electricity conversion efficiency of 6.5% under irradiation of AM 1.5 (100 mW/cm²).     

Nanostructured composite ceramic materials in the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The composite ceramic materials based alumina and zirconia in the monoclinic form (10 wt %) or the tetragonal form stabilized by yttrium (7–45 wt %) are produced from metastable nanopowders through magnetic pulsed compaction followed by free sintering. The specific features revealed in the shrinkage are investigated at temperatures in the range 1400–1500°C. The development of the microstructure and polymorphic transformations are analyzed using X-ray diffraction and atomic-force microscopy. The fracture toughness and the microhardness of the samples are determined by the indentation technique.     

Novel electrochemical measurements on direct electro-deoxidation of solid TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript> in molten calcium chloride medium

A solid metal oxide cathode undergoes significant chemical changes during the molten salt electro-deoxidation process. The changes in the chemical composition lead to changes in the electrical resistivity and potential of the electrode. Two novel electrochemical techniques, based on these two parameters, have been employed to study the electro-deoxidation of solid TiO₂ and ZrO₂ in molten calcium chloride at 900 °C. The in situ resistance measurements carried out by the IR drop method conclusively proved that TiO₂ electrode remains highly conducting throughout the electro-deoxidation process and hence is amenable for reduction. The ZrO₂ electrode, on the other hand, developed very high resistance midway in the electro-deoxidation, and could not be reduced completely. The resistance measurements give strong indication that the electron-transfer reactions taking place at the cathode determine the rate and efficiency of the electro-deoxidation process to a great extent. The low-current galvanostatic electro-deoxidation of TiO₂ electrodes, in conjunction with a graphite pseudo reference electrode to monitor the half cell potentials, showed that the metal oxide passes through two stages during the electrolysis; a high current, low resistant stage 1, where Ca²⁺ ions are inserted to the metal oxide cathode to produce different intermediate compounds and stage 2 where electro-deoxidation of the cathode take place continuously. Removal of oxygen, from the cathode, in stage 1 of the electro-deoxidation is considered to be insignificant. The anodic and cathodic voltages in this stage remained more or less stable at ~1.4 V and ~−1 V, respectively. When the oxygen ions in the melt were depleted at the end of this stage, both the anode and cathode potentials were increased in the anodic direction and this behaviour suggested that the graphite pseudo reference electrode was changed from a C/CO electrode in stage 1 to a Ca²⁺/Ca electrode in stage 2.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite oxide and its photocatalytic degradation of rhodamine B

The composite semiconductor photocatalyst TiO₂/SiO₂ was prepared by template-hydrothermal method using carbon spheres as the template. The structural and optical properties of TiO₂/SiO₂ were characterized by XRD, SEM, BET, UV–Vis DRS, TG-DTA, PL techniques. The formation of hydroxyl radical on the surface of TiO₂/SiO₂ was studied with terephthalic acid as the probe molecule, combined with fluorescence technique. The results showed that the specific surface area of TiO₂/SiO₂ composite was 327.9 m²/g, and the specific surface area of TiO₂/SiO₂ was larger than that of pure TiO₂. Photocatalytic degradation of rhodamine B showed that TiO₂/SiO₂ composite oxide under visible light illumination 40 min, the degradation rate was 98.6 % and the degradation rate of pure TiO₂ was only 11.9 %. The apparent first-order rate constant of TiO₂/SiO₂ was 33 times that of pure TiO₂ and more than 6 times that of P25 when the molar ratio of Ti to Si was 1:1 under visible light irradiation. Moreover, it’s also as much as 5 times that of pure TiO₂ and is more than 1 times that of P25 under UV light irradiation 25 min. Based on the experimental results, ^·O₂ ^? and h⁺ were suggested to be the major active species which was responsible for the degradation reaction. The increased photocatalytic activity of TiO₂/SiO₂ may be mainly attributed to effectively suppressing the recombination of hole/electron pairs. After the photocatalyst TiO₂/SiO₂ was reused 5 times, the degradation rate of rhodamine B could reach 89.2 % under visible light irradiation. Moreover, The composite semiconductor photocatalyst TiO₂/SiO₂ was selective towards the degradation of rhodamine B.     

Theory of the Structure of Coherent Boundaries in ZrO<Subscript>2</Subscript> Nanoparticles

A general algorithm is proposed for constructing coherent boundaries. This algorithm is based on the interrelation between the spatial coherence of structural fragments in nanoparticles and the geometric connection in the corresponding associated bundle. A local approach is used to describe the structure of coherent boundaries in zirconia nanoparticles. The inference is made that the models of structures thus obtained should be preferred over the models constructed in terms of the theory of coincident site lattice.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Shevchenko, Samoilovich, Talis, Madison.     

Mechanochemical synthesis of solid solutions based on ZrO<Subscript>2</Subscript> and their electrical conductivity

Zirconia-and scandia-based complex solid solutions predominantly with a monoclinic structure are prepared by mechanochemical synthesis. The dense ceramic materials, which, for the most part, have a cubic structure with grain sizes of 250–400 nm and possess good mechanical properties, are produced by sintering submicron fractions of the powders under relatively mild conditions at temperatures of 1633–1653 K. It is revealed that the powders are characterized by nanostructuring due to the complex composition and the chemical inhomogeneity. This nanostructuring is partially retained upon rapid sintering of the ceramic powders. The nanostructured ceramic materials possess a high low-temperature conductivity, which decreases after annealing. Unlike conventional ceramic materials, the nanostructured ceramic materials have identical activation energies for bulk and grain-boundary electrical conduction. The high-temperature electrical conductivity of the nanostructured ceramic materials is rather low because of the small grain sizes and impurities of the monoclinic phase.     

Physicochemical properties of nanocrystalline composites based on ZrO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO₂-Al₂O₃-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO₂, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.     

Phase Transformations in Stabilized ZrO<Subscript>2</Subscript> - Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Compositions

Data on interactions in the ZrO₂ - Fe₂O₃ system stabilized by oxides in a high-temperature form at 1750°C are obtained. Of all zirconia-based compositions, only magnesium-zirconium cubic solid solution enters into an active reaction with Fe₂O₃ to yield MgFe₂O₄. The solid solutions formed by ZrO₂ with oxides of yttrium, neodymium, and calcium resist degradation by attack from Fe₂O₃; part of iron oxide undergoes dissolution in cubic ZrO₂. __________ Translated from Novye Ogneupory, No. 9, pp. 40 – 43, September, 2005.     

Al-doped TiO<Subscript>2</Subscript> mesoporous materials: synthesis and photodegradation properties

Aluminium-doped TiO₂ mesoporous material was successfully fabricated by solid-state reaction with cetyltrimethylammonium bromide as a template agent and tetrabutyl orthotitanate as a precursor. The characteristic results from low-angle and wide-angle X-ray diffraction, high resolution transmission electron microscopy and energy dispersive spectroscopy, N₂ absorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet visible light spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the mesoporous architecture of aluminium-doped TiO₂ was composed of crystal wall and micro-/mesopore formed gradually by the mesopore degradation of anatase TiO₂, and aluminium had been doped into the framework of anatase TiO₂. The mesoporous Al-doped TiO₂ material, not only possessed high thermal stability hexahedral mesostructure, large BET surface area and narrow distribution of pore size, but also showed excellent photodegradation behavior for Congo Red. Furthermore the medium UV–Vis absorption peak of mesoporous aluminium-doped TiO₂ in the range 210–370 nm was the absorption peak of aluminium oxide nanoparticles locating the extraframework of TiO₂. A small quantity of aluminium doped into anatase TiO₂ could obviously improve photodegradation activity, and the photodegradation activity of aluminium-doped TiO₂ was higher than that of pure TiO₂.     

Phase separation in melts of the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The morphology of the quenched and slowly crystallized samples in the ZrO₂-Al₂O₃ system is investigated in the composition range 25–70 wt % ZrO₂. It is revealed that, irrespective of the cooling rate, the samples contain large baddeleyite (or corundum) crystals, eutectic mixtures, and characteristic regions of intergrown elongated baddeleyite and corundum grains with micron sizes. These regions have the same phase composition at any initial ratio between zirconium and aluminum oxides and at any cooling rates of the melt. A hypothesis is put forward that these regions are products of the decomposition of ZrO₂ · 2Al₂O₃ associates.     

Product Selectivity as a Function of ZrO<Subscript>2</Subscript> Phase in Cu/ZrO<Subscript>2</Subscript> Catalysts in the Conversion of Cyclohexanol

The influence of ZrO₂ phase on the product selectivity arising from the preparation method of Cu/ZrO₂ is studied in the gas phase conversion of cyclohexanol. This study results are supported by NH₃-TPD, XRD, pyridine-FTIR and N₂O pulse chemisorptions measurements. However, N₂O pulse chemisorptions studies did not reveal significant differences between the two catalysts. The product selectivity is completely dependent on the ZrO₂ phase which ultimately led to the differences in the acidic properties observed through NH₃-TPD and pyridine-FTIR experiments. Catalyst poisoning experiments using NH₃ co-feeding brought a reversal in the product selectivity.

Graphical Abstract

Cu/ZrO₂ catalyst prepared by impregnation method containing monoclinic ZrO₂ yields cyclohexanone and Cu/ZrO₂ catalyst prepared by coprecipitation method with tetragonal ZrO₂ phase possessing strong acidic sites yields benzene when cyclohexanol is contacted in vapour phase conditions

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Geometrical structural complexes of ZrO<Subscript>2</Subscript> nanoparticles

It is demonstrated that the structural inhomogeneity of the nanostate is a fundamental property and can be adequately explained in terms of the algebraic geometry when the four-dimensional fiber space is chosen as a hypothetical praphase of a nanoparticle. Zirconia nanoparticles ZrO₂ with coherent boundaries between their constituent fragments are treated as cross sections of this praphase by three-dimensional Euclidean hyperplanes. The monoclinic, tetragonal, and orthorhombic zirconia structures are assembled from the capped octahedra Z7 and the Bernal polyhedra Z8 and Z9 that are geometrical structural complexes (building blocks) of fluorite-like structures. The interrelated constructions of finite projective geometries are determined. These constructions make it possible to specify graphs of the Z7, Z8, and Z9 polyhedra and to simulate the corresponding ZrO₂ phases as fiber bundles associated with one principal fiber bundle, namely, the ZrO₂ praphase. A priori possible mutual transformations in zirconia are considered, and new structural forms of nanoparticles assembled from the Z7, Z8, and Z9 polyhedra are predicted.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Shevchenko, Samoilovich, Talis, Madison, Shudegov.     

Investigation into the phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> system

Nanopowders of solid solutions with different compositions are prepared in the zirconia-enriched region of the ZrO₂-CeO₂ system. The crystallization of these powders and the formation of the monoclinic, cubic, and tetragonal solid solutions of the composition (Zr_{1 – x} Ce_x)O₂ are investigated. It is found that the unit cell parameters of the solid solutions increase as the cerium content increases. This confirms the fact that cerium ions [r(Ce⁴⁺) = 1.11 ] substitute for zirconium ions [r(Zr⁴⁺) = 0.98 ] in these solid solutions. The average size of crystallites of the solid solutions under investigation increases from 5 to 60 nm in the temperature range 500–1200°C.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Panova, Glushkova, Nefedova.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Electrochemical preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite film and its high activity toward the photoelectrocatalytic degradation of methyl orange

Uniform TiO₂/SiO₂ composite films were prepared on ITO substrates by electrodeposition, and highly photoelectrocatalytic (PEC) activity of the composite films was observed toward the degradation of methyl orange (MO) in aqueous solutions. It was further found that their PEC activity was dependent on the electrodeposition parameters including deposition time, solution pH and SiO₂ content. Under the optimized condition, the PEC degradation of MO on TiO₂/SiO₂ composite film electrode could be enhanced about 14 times relative to that on neat TiO₂ film electrode. The high PEC activity of the TiO₂/SiO₂ composite film electrode was mainly attributed to the enhancement of the charge separation of photo-generated electron-hole pairs by the dispersion of SiO₂ nanoparticles in the TiO₂ matrix with the aid of the applied electric field.     

Dye sensitized CO<Subscript>2</Subscript> reduction over pure and platinized TiO<Subscript>2</Subscript>

TiO₂ thin and thick films promoted with platinum and organic sensitizers including novel perylene diimide dyes (PDI) were prepared and tested for carbon dioxide reduction with water under visible light. TiO₂ films were prepared by a dip coating sol–gel technique. Pt was incorporated on TiO₂ surface by wet impregnation [Pt(on).TiO₂], or in the TiO₂ film [Pt(in).TiO₂] by adding the precursor in the sol. When tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate was used as sensitizer, in addition to visible light activity towards methane production, H₂ evolution was also observed. Perylene diimide derivatives used in this study have shown light harvesting capability similar to the tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate.     

Microstructure and electric conductivity of composite (BeO + TiO<Subscript>2</Subscript>) ceramics

Specimens of composite (BeO + TiO₂) ceramics with TiO₂ added in an amount of 5, 10, 20, 30, and 40 mass% are obtained. The temperature dependence of the conductivity of the (BeO + 30 mass % TiO₂) ceramics is studied. Conduction is ensured by the titania additive present in the ceramics in a strongly reduced state. The maximum temperature (950 K) at which the (BeO + 30 mass % TiO₂) ceramics preserves its conductive properties in air for a long time and, possibly, the capacity to efficiently absorb microwave radiation is determined. Heating in air at a temperature exceeding 960 K is accompanied by the processes of oxidation of reduced TiO₂, which causes disordering of the structure and lowering of the conductivity. An electron microscope study is used to show that the distribution of TiO₂ in the BeO of the [BeO + (5, 10, and 30 mass %) TiO₂] system is nonuniform; inclusions of large regions of grouped TiO₂ microcrystals are encountered. This affects the physicochemical properties of the ceramics, the thermal and electrical conductivities in particular. In order to ensure a uniform distribution of TiO₂ in the volume of the ceramics it is recommended to introduce the dioxide into the composition of the BeO powder from solutions (hydrochemical method). __________ Translated from Novye Ogneupory, No. 11, pp. 68–74, November, 2007.