Structural and electrosurface characteristics of titanium dioxide xerogel prepared by the sol–gel method

Stable highly concentrated TiO₂ sol has been synthesized using binary titanyl ammonium sulfate monohydrate, (NH₄)₂TiO(SO₄)₂ · H₂O. Treatment of the sol with an ammonia solution has yielded a stable hydrogel, which, after being dried, is transformed into a TiO₂ xerogel. Study of the structure-related sorption and crystalline-chemical properties of the synthesized xerogel has shown that it represents a semicrystalline micro/mesoporous material with a rather developed specific surface area (S_sp = 120 m²/g). According to potentiometric titration data, the point of zero charge (PZC) of this material is located at pH 3.9. Measurements of the electrophoretic mobility (by microelectrophoresis) of TiO₂ xerogel particles in solutions of HCl, NaOH, and salts of mono-, bi-, and trivalent cations have shown that (1) the isoelectric point (IEP) of the particles lies in the vicinity of pH 6.2, i.e., at a much higher pH than that for PZC; (2) the presence of increasing amounts of 1: 1 and 2: 1 electrolytes causes a gradual and a dramatic reduction in the ζ potential of the particles, respectively; and (3), in the presence of an electrolyte with a trivalent counterion, the surface charge is reversed. The behavior of TiO₂ xerogel in an electric field is similar to that of lyophobic particles, with the difference that there is no maximum in the ζ potential versus 1: 1 electrolyte concentration dependence and the measured IEP of the xerogel is much higher than its PZC. Possible reasons for this discrepancy have been discussed.     

Study of tin dioxide–sodium stannate composite obtained by decomposition of peroxostannate as a potential anode material for lithium-ion batteries

A tin dioxide–sodium stannate composite has been obtained by the thermal treatment of sodium peroxostannate nanoparticles at 500°C in air. X-ray powder diffraction study has revealed that the composite includes crystalline phases of cassiterite SnO₂, sodium stannate Na₂Sn₂O₅, and sodium hexahydroxostannate Na₂Sn(OH)₆. Scanning electron microscopy has shown that material morphology does not change considerably as compared with the initial tin peroxo compound. Electrochemical characteristics have been compared for the anodes of lithium-ion batteries based on tin dioxide–sodium stannate composite and anodes based on a material manufactured by the thermal treatment of graphene oxide–tin dioxide–sodium stannate composite at 500°C in air.     

Nitrogen doping into titanium dioxide by the sol–gel method using nitric acid

N-doped TiO₂ has been prepared by use of sol–gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and nitrous ions were observed by FT-IR measurement during the sol–gel reaction. The N-doping was confirmed by the observation of N–O peaks in the XPS spectrum of the sample heated at 400 °C. The nitrate ion acted as an oxidizer of the ethanol solvent and titanium species. The TiO₂ became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples. These results indicated that the added nitric acid was reduced during the sol–gel transition and heating process, and the resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was confirmed by the degradation of trichloroethylene.     

Molecular interaction between DNA molecules and nanoscale modifications of titanium dioxide with the structures of anatase and η-TiO2

The interaction of linear DNA molecules (hydrolysis products of Lambda phage DNA) with nanoscale modifications of titanium dioxide with anatase and ??-TiO₂ structures is studied. The photosensitization of adsorption and degradation processes of DNA under the effects of visible light is revealed. It is established that the anatase exhibits increased activity towards DNA in a low salt buffer, while ??-TiO₂ has a higher adsorption capacity in a buffer with high ionic strength. Recommendations on the practical application of nanoscale modifications of titanium dioxide with the structures of anatase and ??-TiO₂ are given.     

Effects of diethanolamine on the evolution of silver/titanium dioxide sol–gel process

In order to clarify the effects of diethanolamine (DEA) in the silver (Ag)/titanium dioxide (TiO₂) sol–gel process, sols with and without DEA, and films derived from these sols were prepared. The samples were investigated by X-ray diffraction, transmission electron microscopy, electron diffraction and optical absorption spectra. The results showed that metallic Ag clusters were formed in the sol with DEA and was absent in the sol without DEA. This indicated that DEA worked not only as the stabilizer but also as the reduce agent in Ag/TiO₂ sol–gel process. After annealed, Ag metallic nanoparticles were generated in the films derived from both the sols with and without DEA. The particles in the films derived from the sol with DEA were smaller than those from the sol without DEA. This can be ascribed to the limitation of the growth of Ag cluster formed in the sol with DEA during heat treatment. Mechanisms for the formation of metallic Ag in the Ag/TiO₂ sols and films were discussed. The effects of DEA in the sols and films were studied in detail.     

Photoregulated uptake and release of drug by an organic–inorganic hybrid sol–gel material

A photo-responsive molecularly imprinted sol–gel organic-inorganic hybrid material prepared by covalent imprinting of the template-functional monomer complex formed between 4,4′-dihydroxylazobenzene and ibuprofen was developed to explore the photo-regulated uptake and release of drug by a silicate-based smart molecularly imprinted materials. After imprinting, the template molecules (ibuprofen) were removed via hydrolysis in acid, and accurate cavities were left, which could be used as the receptor recognition sites for ibuprofen. The new organic–inorganic hybrid material shows specific affinity to ibuprofen and reversible uptake and release of ibuprofen upon alternate irradiation at 365 and 440 nm, respectively. The favorable binding strength of the imprinted receptor sites in the molecularly imprinted polymer (MIP) for ibuprofen is found to be 2.28 × 10³ M⁻¹. Density of receptor sites in the MIP material was 4.0 μmol/g—MIP.     

Strengthening of composite materials of the fluorohydroxyapatite–zirconia system by titanium nitride

Composite materials of the ZrO₂–fluorohydroxyapatite (FHA)–titanium nitride (TiN) system have been synthesized and studied. In the course of sintering even in a protective inert medium, the reaction between the components begins at 700°C to give calcium titanates, titanium oxides, and oxygen-deficient zirconia compounds. As a result of working through the procedure of synthesis of ultrafine powders and selecting sintering regimes, including the hot-pressing method, dense composite materials of the FHA–ZrO₂ system containing TiN were obtained with a bending strength of up to 273 MPa and a crack resistance of up to 3.3 MPa m^1/2.     

Carbon dioxide catalytic conversion to nano carbon material on the iron–nickel catalysts using CVD-IP method

The over-consumption of fossil fuels resulted in the large quantity emission of carbon dioxide(CO2), which was the main reason for the climate change and more extreme weathers. Hence, it is extremely pressing to explore efficient and sustainable approaches for the carbon-neutral pathway of CO2 utilization and recycling. In our recent works with this context, we developed successfully a novel chemical vapor deposition integrated process(CVD-IP) technology to converting robustly CO2 into the value-added solid-form carbon materials.The monometallic Fe Ni0–Al2O3(FNi0) and bimetallic Fe Nix–Al2O3(FNi2, FNi4, FNi8 and FNi20) samples were synthesized and effective for this new approach. The catalyst labeled FNi8 gave the better performance, exhibited the single pass solid carbon yield of 30%. These results illustrated alternative promising cases for the CO2 capture utilization storage(CCUS), by means of the CO2 catalytic conversion into the solid-form nano carbon materials.     

Peculiarities of sorption isotherm and sorption chemisms of caesium by mixed nickel–potassium ferrocyanide based on hydrated titanium dioxide

The effect of ⁶⁰Co source γ-radiation on β-carotene and chlorophyll-b solutions and on methyl blue dye fixed on cotton fabric has been investigated by colorimetric measurements. For the three reactive pigments, the result obtained shows that the power-law function can be used to predict the value of color difference according to γ-radiation dose. This same behaviour was observed during examination of many other published data. Based on these observations, the power-law function has been proposed as an empirical distribution for modeling the color variation of biologic molecules as a function of irradiation dose.     

Nickel–cobalt hydroxide catalysts for the cycloaddition of carbon dioxide to epoxides

Research on Chemical Intermediates - Nickel and cobalt bimetallic hydroxides, in which both metal cations present the same oxidation state, were synthesized and characterized by XRD, TGA, TEM, XPS,...     

Updated estimates of the selenomethionine content of NIST wheat reference materials by GC–IDMS

Updated estimates of the selenomethionine content of four NIST wheat reference materials have been obtained by use of a revised gas chromatography–stable-isotope dilution mass spectrometric method. The revised method makes use of digestion with methanesulfonic acid, which enables more complete recovery of endogenous selenomethionine than was previously achieved by overnight denaturing treatment in 0.1 mol L⁻¹ HCl. The NIST wheat reference materials each contain approximately 55% of their total Se content as selenomethionine. Information about forms of Se in reference materials adds value to these materials in Se speciation studies. Estimates of selenomethionine content are also provided for other wheat samples, including several grown under conditions of exposure to high Se levels. These samples also contain approximately 55% of their total Se content as selenomethionine. The consistent level of 55% of total selenium occurring in the form of selenomethionine when the total selenium content varies by a factor of 500 is suggestive of an active mechanism of incorporation of selenium into wheat grain. Figure Selenomethionine content of wheat samples     

Addition of carbon dioxide to epoxides catalyzed by the mixtures of α-amino acids and iodine

Russian Chemical Bulletin - We found a group of available and efficient catalysts for the addition reaction of CO2 to epoxides, which was formed by simple mixing of molecular iodine with...     

Determination of trace europium by use of the new fluorescence system europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate

A new lanthanide-sensitized luminescence system: europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate has been discovered. The spectrofluorimetric properties of the system were studied. The effect of experimental conditions on the fluorescence intensity was defined. Under the optimum conditions, the fluorescence intensity of the system is a linear function of the concentration of europium in the range 5.0×10^–9–1.0×10^–6 mol L^–1 and the detection limit is 1.0×10^–10 mol L^–1. The system was used for the determination of trace amounts of europium in rare earth samples with satisfactory results.     

ESR Approach to the Nature of Solvation by Using s-Butyl n-Heptafluorobutyryl Nitroxide Probe

Because the solvent dependency of aN, g factors and line widths of some bulky and stable di-t-alkyl nitroxides1, ESR has been proved to be a useful tool in searching for the nature of medium effects ( solvation ) to chemical reactivity. A large number of fluorinated nitroxides with a wide variety of structures have been generated and subjected to extensive studies in our laboratory2. Amongst, t-butyl perfluoroalkyl nitroxides, much less hindered, with noβ-H atoms, have been employed as sp…     

Estimation of the homogeneity of reference materials by SS–ETAAS and use of the "tape-sandwich" sample-introduction technique

The so called "tape sandwich", a novel sample-introduction technique developed for SS-ETAAS, has been employed in a study of the microheterogeneity of some biological CRM. Pb, Cd, and Cr were measured by use of a laboratory-assembled instrument with graphite-cup atomizer. Aqueous standards were found satisfactory for calibration. The average mass of sub-samples atomised was in the range 0.250-0.660 mg+/-30%. The relative sampling error found for the CRM investigated varied from 15-34%. Calculated relative homogeneity constants of the order of 4-21 mg(1/2) were obtained, and were reduced considerably by reduction of the particle size. The minimum sample sizes representative of the CRM were, with one exception, much lower (11-75 mg) than those recommended in the documentation accompanying the standards (100-200 mg). In a Chinese hair reference sample Cr data were normally distributed but the presence of nuggets was observed for Cd and Pb; this was associated with severe radial and longitudinal gradients of these elements in hair.     

Some questions on the exchange contribution to the effective potential of the Kohn–Sham theory

The current success of Density Functional Theory applications hinges upon the availability of explicitly density-dependent functionals to self-consistently solve a set of one-electron equations, the Kohn–Sham (KS) equations, which determine the occupied orbitals and its associated electronic density. In KS theory, a local exchange potential is proposed as part of an effective potential. This potential is compared to the exchange operator of the Hartree–Fock theory, which is of a non-local nature. The present paper discusses the variational framework of the KS equations, and the equivalence between both exchange potentials within a correlation-free theory. The common difficulties of current local exchange functionals to correctly simulate the non-locality of the exchange energy density in chemical systems are also analyzed and explained through an exactly solvable model. We give then numerical arguments and conclude by analyzing the performance of various commonly used approximations to exchange functionals.