Photooxidation of Ethylbenzene with TiO<Subscript>2</Subscript> and Metal Coated TiO<Subscript>2</Subscript> and its Kinetics

Summary. Photooxidation of ethylbenzene with oxygen to give ethylbenzene hydroperoxide has been achieved in a stirred photochemical reactor that was cooled by a water system by irradiation with a 400W high-pressure mercury lamp and using TiO₂ powder and metal coated TiO₂. The effects of the amount of copper or silver coated on TiO₂ and of the temperature on the rate of oxidation have been investigated. It is suggested that thermal cleavage of the O–O bond and photochemically generated singlet oxygen should be considered as the initiating step in a radical chain mechanism. An optimum loading of 6% Ag or 4–5% Cu was observed for photooxidation of ethylbenzene.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.     

Electrochemical vapor generation of selenium species after online photolysis and reduction by UV-irradiation under nano TiO<Subscript>2</Subscript> photocatalysis and its application to selenium speciation by HPLC coupled with atomic fluorescence spectrometry

An online UV photolysis and UV/TiO₂ photocatalysis reduction device (UV–UV/TiO₂ PCRD) and an electrochemical vapor generation (ECVG) cell have been used for the first time as an interface between high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS) for selenium speciation. The newly designed ECVG cell of approximately 115 L dead volume consists of a carbon fiber cathode and a platinum loop anode; the atomic hydrogen generated on the cathode was used to reduce selenium to vapor species for AFS determination. The noise was greatly reduced compared with that obtained by use of the UV–UV/TiO₂ PCRD–KBH₄–acid interface. The detection limits obtained for seleno-DL-cystine (SeCys), selenite (Se^IV), seleno-DL-methionine (SeMet), and selenate (Se^VI) were 2.1, 2.9, 4.3, and 3.5 ng mL^–1, respectively. The proposed method was successfully applied to the speciation of selenium in water-soluble extracts of garlic shoots cultured with different selenium species. The results obtained suggested that UV–UV/TiO₂ PCRD–ECVG should be an effective interface between HPLC and AFS for the speciation of elements amenable to vapor generation, and is superior to methods involving KBH₄.     

Solvothermal preparation of copper(II) porphyrin-sensitized mesoporous TiO<Subscript>2</Subscript> composites: enhanced photocatalytic activity and stability in degradation of 4-nitrophenol

Four new copper(II) porphyrins CuPp(1, 2, 3, 4) with a different number of peripheral ester groups were synthesized and used to sensitize the mesoporous TiO₂ under solvothermal condition, and accordingly, four mesoporous CuPp(1, 2, 3, 4)/TiO₂ composites were obtained. These composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, BET nitrogen adsorption–desorption isotherms (BET), UV–vis diffuse reflectance spectroscopy (UV–vis-DRS), and Fourier-transform infrared spectroscopy (FT-IR). The results showed the crystal structure and morphology of mesoporous TiO₂ were not affected by the porphyrin existence on its surface. The photocatalysis properties of mesoporous TiO₂ and CuPp(1, 2, 3, 4)/TiO₂ have been evaluated by conducting the photocatalytic degradation of 4-nitrophenol (4-NP) under visible-light irradiation, and the result showed their higher photocatalytic activities and the order is: CuPp(4)/TiO₂ > CuPp(3)/TiO₂ > CuPp(2)/TiO₂ > CuPp(1)/TiO₂ ? TiO₂. The probable reasons are their large surface area and different number of peripheral groups in CuPp, which separate electron–hole pairs efficiently. The repetition test of CuPp(1, 2, 3, 4)/TiO₂ composites demonstrated that they still maintained superior photocatalytic activity over six recycles.     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

Synthesis of nonequilibrium Ir<Subscript>x</Subscript>Re<Subscript>1-x</Subscript> solid solutions. Crystal structure of [Ir(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl]<Subscript>2</Subscript>[ReCl<Subscript>6</Subscript>]Cl<Subscript>2</Subscript>

Synthesis of five binary complex salts with an [Ir(NH₃)₅Cl]²⁺ complex cation is described. The counterions are [ReCl₆]^2–, [IrCl₆]^2–, [ReBr₆]^2–, and Cl^–. A polycrystal X-ray diffraction study has been performed for [Ir(NH₃)₅Cl]₂[ReCl₆]Cl₂, and its crystal structure has been determined. A series of Ir _x Re_1–x phases (0.5 x > 1) were obtained by reductive thermolysis. For the Ir-Re system, the history of the V/Z(x) dependence has been refined.Original Russian Text Copyright © 2004 by S. A. Gromilov, S. V. Korenev, I. V. Korolkov, K. V. Yusenko, and I. A. BaidinaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 508–515, May–June 2004.     

Oxidation of aromatic compounds: XII. Regio- and stereoselective oxidative dimerization of alkyl 3-arylpropynoates in the system CF<Subscript>3</Subscript>CO<Subscript>2</Subscript>H-CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>-PbO<Subscript>2</Subscript>

Regio- and stereoselective oxidative dimerization of alkyl 3-arylpropynoates in the system CF₃CO₂H-CH₂Cl₂-PbO₂ (1–30 h, 0–20°C) leads to dialkyl (E)-2,3-bis(arylcarbonyl)-2-butene-1,4-dioates with trans arrangement of the substituents at the double bond.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 9, 2004, pp. 1329–1333.Original Russian Text Copyright © 2004 by Savechenkov, Vasilev, Rudenko.For communication XI, see [1].     

Effect of pretreatment on microstructure and photocatalytic activity of kaolinite/TiO<Subscript>2</Subscript> composite

Kaolinite/TiO₂ composites were prepared by using sol-gel method and raw kaolin, pretreated kaolinite and tetrabutyl titanate as the main raw materials. X-ray diffractometer, field-emission scanning electron microscope and infrared spectrometer analysis were carried out to characterize the phase composition and microstructure of the samples. The photocatalytic performance of the kaolinite/TiO₂ composites were evaluated by degrading the methylene blue (MB) and phenol aqueous solution, respectively. The results show that intercalation and exfoliation reduced the size and thickness of kaolinite particles. Acid treatment improved the distribution and the loading quantity of TiO₂ grains. When the kaolinite/TiO₂ composites were calcined at 500?°C, the tetragonal structure of anatase particles of 30–100?nm in size were obtained, but the exfoliated kaolinite crystals were damaged. The degradation rate of MB increased gradually with the extension of photocatalytic reaction time and the enhancement of photocatalyst dosage. The adsorption performance of acid-treated kaolinite/TiO₂ composite (AKT) was nearly the same as that of raw kaolin/TiO₂ composite (RKT), but that of the exfoliated kaolinite/TiO₂ composite (EKT) was the most excellent. The photocatalytic performance of AKT and EKT were better than that of RKT, and AKT exhibited the optimum property. Under a certain photocatalyst dosage and photocatalysis time, the absorption rate and the degradation rate decreased gradually with the enhancement of initial concentration of MB. Similar result was also acquired for the degradation of phenol. Both the acid treating and the exfoliating to kaolinite enhanced the photocatalytic performance of the kaolinite/TiO₂ composite photocatalysts, but acid treatment may be more helpful to the preparation of high performance kaolinite/TiO₂ composite photocatalyst.

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Phase equilibria in the CdI<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The phase diagram of the system CdI₂-Bi₂O₃ is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. As a result of the synthetic and peritectic interactions, two incongruently melting intermediate phases i.e. phase A — CdI₂·2Bi₂O₃ and phase B — CdI₂·4Bi₂O₃ (stable in the temperature interval 370–850°C) are formed.The phase A exists in two polymorphic forms with a temperature of the phase transition T =320–370°C. The unit cell parameters at low temperature modification of -CdI₂°2Bi₂O₃ were determined. (a=1.032 nm, b=1.046 nm, c=1.046 nm, =115.02°, =109.11° and =82.04°). The phases A and B have fields of homogeneity.The authors acknowledge thankfully the financial support for this work from the Ministry of Education and Science (Fond Scientific investigations — contract TN-1102).     

Interaction of N<Subscript>2</Subscript> with the acid sites of oxides

Nitrogen adsorption on SiO₂, -Al₂O₃, TiO₂, and sulphated zircona (SO _2- ⁴ /ZrO₂) is studied by Fourier transform IR spectroscopy. Integrated absorption coefficients for the bands due to the N—N vibrations in nitrogen complexes with Brønsted and Lewis acid sites are determined. A general correlation between integrated absorption coefficients and the positions of N—N bands of nitrogen interacting with the above sites in zeolites and oxides is discussed. The orientation of a nitrogen molecule relative to Brønsted and Lewis acid sites is calculated ab initio using a 6-31G^** basis set.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 115–121.Original Russian Text Copyright © 2005 by Malyshev, Paukshtis, Malysheva.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

Crystal structure of the synthetic analog of radtkeite Hg<Subscript>3</Subscript>S<Subscript>2</Subscript>Cl<Subscript>1.00</Subscript>I<Subscript>1.00</Subscript>

The results of structural studies of the synthetic analog of the radtkeite mineral Hg₃S₂Cl_1.00I_1.00 are analyzed. The crystal structure of the compound has been refined; the unit cell parameters are a _m = 16.827(4) , b _m = 9.117(1) , c _m = 13.165(5) , = 130.17(2)°, V = 1543.3(8) ³, space group C2/m, Z = 8, R = 0.0527. A possible transition a ₀ = a _m; b ₀ = a _m + 2c _m; c ₀ = –b _m to the pseudo-orthorhombic F cell previously determined for radtkeite, where one of the angles ( ₀ ) is slightly different from 90° (89.55°), has been found. Each sulfur atom in the structure is bonded to three mercury atoms, forming SHg₃ umbrellas with distances 2.240(6) –2.474(8) and angles HgSHg 94.7(2)°–102.9(2)°. The SHg₃ fragments are linked through Hg vertices to form corrugated [Hg₁₂S₈] layers. The halogen atoms lie inside and between the [Hg₁₂S₈] layers; the distances are Hg-Cl and Hg-I 2.783(7) , 2.961(7) , and 3.083(4) –3.311(3) , respectively.Original Russian Text Copyright © 2004 by N. V. Pervukhina, S. V. Borisov, S. A. Magarill, D. Yu. Naumov, V. I. Vasiliev, and B. G. NenashevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 755–758, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Quantum-chemical study of C<Subscript>n</Subscript>F2<Subscript><Emphasis Type="Italic">n</Emphasis>+2</Subscript> conformers. Structure and IR spectra

Quantum-chemical calculations of the geometrical structure and vibrational spectra of C_nF_2n+2 oligomers (n = 5–8) in the chain and branched conformations are reported. The lengthening of the chain of C_nF_2n+2 does not substantially affect the geometrical parameters of the oligomers. In all cases under study, the most optimal structure of the molecule is a zigzag chain with bond lengths R(C-C) = 1.53 –1.54 and R(C-F) = 1.36 –1.34 ; the chain is rolled into a helix, which makes an angle of 17° with the plane. The IR spectra are sensitive to the structural deficiency of oligomers C_nF_2n+2 associated with the lateral trifluoromethyl groups formed in the chain; the spectra can be used for revealing defects of this type in the structure of polytetrafluoroethylene (PTFE). The possibility of defects associated with the lateral CF₃ groups in the structure of PTFE and its low-temperature modifications is explained based on the calculated total energies of C_nF2 _n+2.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. Yu. Beloliptsev, S. G. Kozlova, and V. M. BuznikTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 632–643, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Influence of ThO<Subscript>2</Subscript> on the photocatalytic activity of TiO<Subscript>2</Subscript>

Microcomposites consisting of TiO₂ (or Ce-doped TiO₂) and ThO₂ (0.5–2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of ThO₂. X-ray diffraction study reveals the effects of ThO₂ (compared to the ThO₂-free TiO₂, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO₂ obtained at 550°C and containing 1% ThO₂. The composite exhibits activity in dark, also. The presence of Ce⁴⁺ ions is not an obligatory requirement for the realization of the ThO₂ effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO₂.      

Crystal structure of Ba(VUO<Subscript>6</Subscript>)<Subscript>2</Subscript>

The crystal structure of Ba(VUO₆)₂ was determined by X-ray diffraction at 243 K: monoclinic crystal system, space group P2₁/c, unit cell parameters a=6.4992(6) Å, b=8.3803(8) Å, c=10.4235(9) Å, =104.749(2) °, Z=2. The structure contains close-packed [VUO₆] ₂ ^- layers formed by the dimers of the flattened U₂O₁₂ pentagonal bipyramids and by the dimers of V₂O₈ square pyramids. The neighboring layers are bound by the statistically distributed barium atoms.Original Russian Text Copyright © 2004 by E. V. Alekseev, E. V. Suleimanov, E. V. Chuprunov, and G. K. FukinTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 544–548, May–June 2004.     

Influence of ZrO<Subscript>2</Subscript> on the physicochemical properties of the ZrO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> binary system

A series of ZrO₂-TiO₂ mixed oxides with different weight ratios (5, 20, and 30% ZrO₂) were prepared by wet impregnation of TiO₂-P25 Degussa with certain amounts of ZrO(NO₃)₂·6H₂O (Fluka) dissolved in deionised water. The samples were characterized by the XRD, , , , and BET methods. An increase in ZrO₂ content shifted the phase transition temperature (anatase into rutile) toward higher temperatures. X-ray diffraction using an Anton Paar XRK900 reactor chamber indicated that, in the case of samples containing ZrO₂, an additional diffraction peak appeared after cooling down to 25°C. This peak could be attributed to a polymorph of TiO₂ such as in the single crystal of anatase or hexagonal form of TiO₂ which appears in the presence of ZrO₂. Generally, the preparation of dioxide systems can modify the properties of pure compounds or generate new catalytic sites as a result of strong interaction between ZrO₂ and TiO₂ oxides. The binary systems exhibit advantages like strong acidity, extended specific surface area, and high thermal stability in comparison with TiO₂. The article is published in the original.     

Interatomic interactions and electronic structure of NbSe<Subscript>2</Subscript> and Nb<Subscript>1.25</Subscript>Se<Subscript>2</Subscript> nanotubes

Atomic models of achiral NbSe₂ nanotubes are suggested. Band structure calculations have been performed to investigate the electronic structure and determine the parameters of interatomic interactions. The distribution of the density of states and pair bond occupancies of NbSe₂ nanotubes are analyzed in relation to the type of the atomic configuration and the tube diameter; the results are compared with the band structure of the 2H-NbSe₂ crystal. Calculations have been carried out on hypothetical superstoichiometric nanotubes with a formal composition Nb_1.25Se₂ as possible quasi-one-dimensional nanoforms of autointercalated niobium diselenide.Original Russian Text Copyright © 2004 by A. N. Enyashin, V. V. Ivanovskaya, I. R. Shein, Yu. N. Makurin, N. I. Medvedeva, A. A. Sofronov, and A. L. IvanovskiiTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 579–588, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Comparative Study of the Oxygen Storage Capacity of Pt/M<Subscript>x</Subscript>O<Subscript>y</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Systems

The oxygen storage capacity of 1% Pt/15% M_xO_y/Al₂O₃ systems containing a rare-earth or an alkaline-earth metal oxide or TiO₂ as the oxygen-storing component was studied. Oxygen storage capacity was evaluated as the amount of C₃H₈ reacting at 400°C with oxygen that was taken up by the catalyst during oxidative treatment. The systems containing a rare-earth metal oxide or TiO₂ possess the highest oxygen storage capacity among the catalysts examined (80 and 75 µmol C₃H₈/g Cat, respectively). Of the BaO and SrO systems, the latter is of interest, although its oxygen storage capacity (∼27 µmol C₃H₈/g Cat) is somewhat lower than the oxygen storage capacity of any rare-earth metal oxide or the TiO₂ system.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 585–589.Original Russian Text Copyright © 2005 by Sinel’nikov, Tolkachev, Stakheev.     

Effect of the potential of an external electron donor on C<Subscript>2</Subscript>H<Subscript>2</Subscript> reduction catalyzed by the nitrogenase active center (FeMoco) isolated from the enzyme

The effect of potential value and chemical properties of an external electron donor on C₂H₂ reduction catalyzed by nitrogenase active center (cluster [(₆-N)Fe₇MoS₉·homocitrate] FeMoco isolated from the enzyme) has been investigated in the presence of proton donors of different acidity. The temperature—reaction rate dependences of these reactions have been studied. It has been shown that the rate-limiting steps of the reactions differ depending on the proton donor used. When thiophenol or water are used as proton donors, and electrochemical step — the electron transfer from cathode to adsorbed catalytic cluster — has been found to be a rate-limiting one. The effective activation energy of ethane formation as a product of four-electron C₂H₂ reduction is found to be 1.5 times lower than that of ethylene, namely, 13 kcal mol^–1. When stronger acid, pentafluorothiophenol, is used as a proton donor, the chemical step of intramolecular rearrangement of the catalyst—substrate complex taking place in solution becomes a rate-limiting one. The effective activation energies of both ethylene and ethane become equal to 32 kcal mol^–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1583–1591, August, 2004.     

Reactions in AB<Subscript>5</Subscript>-NH<Subscript>3</Subscript> systems

Treatment of intermetallic compounds LaNi₅ and SmCo₅ with ammonia (initial ammonia pressure 0.6– 0.7 MPa) in the presence of 10 wt% NH₄Cl as an activator results in hydrogenation of these compounds or, in the case of SmCo₅, in disproportionation to form Sm₂Co₇H_x. In some cases, the intermetallic matrix decomposes under this treatment.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1765–1769.Original Russian Text Copyright © 2004 by Fokin, Shulga, Tarasov, Fokina, Korobov, Burlakova, Shilkin.This revised version was published online in April 2005 with a corrected cover date.