Preparation of Co–Al and Ni–Al layered double hydroxide thin films by a sol–gel process with hot water treatment

Using hot water treatment of sol–gel derived precursor gel films, Co–Al and Ni–Al layered double hydroxide (LDH) thin films were prepared. The precursor gel films of Al₂O₃–CoO or Al₂O₃–NiO were prepared from cobalt or nickel nitrates and aluminum tri-sec-butoxide using the sol–gel method. Then, the precursor gel films were immersed in a NaOH aqueous solution of 100 °C. Nanocrystallites of Co–Al and Ni–Al LDH were precipitated with the hot water treatment with NaOH solution. The largest amounts of nanocrystals were obtained with a solution of pH = 10 for Co–Al LDH, and with that of pH = 9 for Ni–Al LDH. X-ray diffraction measurements confirmed that this process formed CO₃ ²⁻ intercalated LDHs. Both Co–Al and Ni–Al LDH thin films were confirmed to work as electrodes for electrochemical devices by cyclic voltammogram measurements.     

Rubidium-cationic conductance in the systems Rb2 ? 2xAl2 ? xAxO4 (A = P, V)

RbAlO₂-based solid solutions are synthesized in the systems Rb_{2 − x} Al_{2 − x} A _x O₄ (A = P, V). Temperature and concentration dependences of their conductance are studied; the rubidium-cationic character of the conductance is corroborated. The high ionic conductivity of the synthesized phases (∼5 × 10⁻³ S cm⁻¹ at 300°C, ∼2 × 10⁻² S cm⁻¹ at 700°C) is caused by (a) formation of rubidium vacancies as a result of the replacing of Al³⁺ ions by fivefold-charged cations of phosphorus or vanadium and (b) disordered crystal structure of γ-KAlO₂ type. The obtained data are compared with the results of the studying of similar systems. Original Russian Text ? G.Sh. Shekhtman, E.I. Volegova, E.I. Burmakin, 2009, published in Elektrokhimiya, 2009, Vol. 45, No. 4, pp. 495–499.     

Photostimulated changes in WO3 nanosized films

During the irradiation of WO₃ films d = 7–160 nm thick by light at λ = 320 nm (I = (1.5–7) × 10¹⁵ quantum cm⁻² s⁻¹), absorption band at λ = 850 nm appeared along with absorption band edge shift to shorter waves. The subsequent irradiation of samples at λ = 850 nm caused the disappearance of the longwave absorption band. The intrinsic absorption edge of WO₃ films was determined (λ = 320 nm). The degree of transformations of WO₃ films increased under atmospheric conditions as the intensity of incident light and the time of irradiation (1–140 min) grew and as film thickness decreased. A mechanism of photochemical transformations of WO₃ films was suggested. This mechanism included the generation of electron-hole pairs, the recombination of part of nonequilibrium charge carriers, the formation of [eV_a²⁺e] centers, and the isolation of photolysis products.     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Kinetic studies on the hydrogenation of nitrate in water using Rh/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Rh-Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Liquid-phase reduction NO ₃ ⁻ using monometallic and bimetallic catalysts (5% Rh/Al₂O₃, 5% Rh-0.5% Cu/Al₂O₃, 5% Rh-1.5% Cu/Al₂O₃, 5% Rh-5% Cu/Al₂O₃ and a physical mixture of 5% Rh/Al₂O₃ and 1.5% Cu/Al₂O₃) was studied in a slurry reactor operating at atmospheric pressure. Kinetic measurements were performed for a low concentration of nitrate (0.4 × 10⁻³−3.2 × 10⁻³ mol dm⁻³) and the temperature range 293–313 K. From the experimental data, it was found that the reduction of nitrate is first order with respect to nitrate. On the basis of the rate constants, the apparent activation energy was established using a graphic method. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 881–886. This article was submitted by the authors in English.     

Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

In situ study of the interaction between <Emphasis Type="Italic">tert</Emphasis>-butyl chloride and aluminum activated with liquid In-Ga eutectic

The interaction between tert-butyl chloride and activated aluminum was studied by attenuated total reflectance Fourier transform infrared spectroscopy near room temperature (18–25°C). A long induction period of ∼240–260 min was observed. The ionic aluminum chloride complexes [Al _n Cl_3n+1]⁻ (n = 1, 2) and the molecular species AlCl₃ were identified at the activated aluminum/tert-butyl chloride interface during the reaction. The formation of the ion in the AlCl₄⁻ ion in the liquid medium and the presence of the same ion and a molecular AlCl₃-tert-butyl chloride complex in the resinous products of the reaction were confirmed by ²⁷Al NMR spectroscopy. The reaction products were analyzed qualitatively by GC/MS. The reactivities of activated aluminum and anhydrous aluminum chloride toward tert-butyl chloride under the same conditions were compared. A distinctive feature of the interaction activated aluminum and tert-butyl chloride is the dominant formation of the AlCl₄⁻ ion. By contrast, the interaction between aluminum chloride and tert-butyl chloride yields the polynuclear ion Al₂Cl₇⁻ and, likely, Al₃Cl₁₀⁻.     

Solid Potassium-Conducting Electrolytes in the System K2 ? 2xAl2 ? xPxO4

New high-conductance potassium-cation solid electrolytes based on potassium aluminate are synthesized by means of partial substitution of five-charged phosphorus cations for three-charged aluminum cations and investigated. The maximum conductivity in the system K_{2 − 2x} Al_{2 − x} P _x O₄ is found to equal 5 × 10⁻³ S cm⁻¹ at 200°C and ∼1 S cm⁻¹ at 700°C, which is one of the best values for potassium solid electrolytes. The principal factors responsible for the high conductance are the stabilization of a high-temperature form of potassium aluminate and the formation of additional vacancies in the potassium sublattice, which occurs during the substitution process Al³⁺ → P⁵⁺ + 2V _K ^′ . __________ Translated from Elektrokhimiya, Vol. 41, No. 12, 2005, pp. 1501–1504. Original Russian Text Copyright ? 2005 by Burmakin, Shekhtman.     

Yb<Superscript>3+</Superscript> → Er<Superscript>3+</Superscript> energy transfer in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and temperature characteristic of near-infrared photoluminescence

For the Er³⁺–Yb³⁺ codoped Al₂O₃ powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb³⁺ to Er³⁺ was detected by a 978 nm laser diode excitation. Compared with that of Er³⁺ doped Al₂O₃ powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er³⁺–Yb³⁺ codoped Al₂O₃ powders at room temperature. The ET coefficient of 2.18 × 10⁻¹⁸ cm³ s⁻¹ from Yb³⁺ to Er³⁺ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation ⁴I_13/2 → ⁴I_15/2 dominated over thermally enhanced phonon-assisted ET in the Er³⁺–Yb³⁺ codoped Al₂O₃.     

Kinetic regularities of thermal transformations in nanosized bismuth films

Transformations in a nanosized bismuth layer are studied by means of optical spectroscopy, microscopy, and gravimetry, depending on the thickness (d = 3–120 nm), thermal treatment temperature (T = 373–673 K) and time (τ] = 0.05–2500 min). It is established that, depending on the initial thickness of the bismuth films and the thermal treatment temperature, the kinetic curves of the degree of transformation are satisfactorily described within linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference for the Bi, Bi₂O₃ films and the photo-electromotive force for the Bi-Bi₂O₃ systems is measured. An energy-band diagram for the Bi-Bi₂O₃ systems is constructed. A model for the thermal transformation of Bi films that includes the stage of oxygen adsorption, the redistribution of charge carriers in the Bi-Bi₂O₃ contact field, and the formation of bismuth(III) oxide is proposed.     

The thermodynamic properties of natural margarite

Thermal, IR spectroscopic, and thermochemical studies of natural brittle mica, margarite Ca_1.00Na_0.10Mg_0.02Al_3.89Fe_0.01³⁺Si_2.03Ti_0.01O₁₀(OH)_1.74F_0.26, were performed. The enthalpy of formation of natural margarite from the elements (−6269 ± 12 kJ/mol) was determined by melt solution calorimetry on a high-temperature heat-conducting Calvet microcalorimeter (Setaram, France). Enthalpy growth over the temperature range 298.15–973 K was determined by the drop method. Equations for the temperature dependences of the enthalpy and heat capacity were obtained, H°(T)−H°(298.15 K), J/mol = 435.21T + 36.46 × 10⁻³ T ² + 109.91 × 10⁵/T − 169863 and C° _p , J/(mol K) = 435.21 + 72.92 × 10⁻³ T − 109.91 × 10⁵/T ². The experimental data were used to estimate the thermodynamic properties of margarite of the theoretical composition, CaAl₂[Al₂Si₂O₁₀](OH)₂.     

Differential kinetic thermal lens determination of aniline and 4-nitroaniline

Thermal lens spectrometry was used for the differential kinetic determination of aniline (over the concentration range of 8 × 10⁻⁴–3.2 × 10⁻³ M) and 4-nitroaniline (2 × 10⁻⁴–1.6 × 10⁻³ M) present in combination in a single sample based on the oxidation reaction with periodate ions in an acidic medium (this determination is not possible with the spectrophotometric monitoring of the rate of reaction). The thermal lens procedure (λ_e = 488.0 nm; 80 mW) was characterized by good performance characteristics in the determination of aniline (c _min = 3 × 10⁻⁴ M; c _d = 8 × 10⁻⁴ M) and 4-nitroaniline (c _min = 7 × 10⁻⁵ M; c _d = 2 × 10⁻⁴ M), simplicity, and rapidity.     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Preparation of superhydrophobic PET fabric from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> hybrid: geometrical approach to create high contact angle surface from low contact angle materials

In this work we prepare high contact Poly Ethylene Terephthalate (PET) fabric surface from low contact angle materials. Superhydrophobic PET fabric is prepared by coating the fabric with hybrid Al₂O₃–SiO₂ sol. In this case, the high contact angle Al₂O₃–SiO₂ hybrid is created from low contact angle Al₂O₃ and SiO₂ precursors. PET treated with hybrid Al₂O₃–SiO₂ exhibit Water Contact Angle (WCA) as 150°, while PET treated with individual Al₂O₃ sol or SiO₂ sol exhibits lower WCA, (Al₂O₃ WCA = 137°; SiO₂ WCA = 141°). FESEM and AFM investigations show that the hybrid Al₂O₃–SiO₂ sol and individual Al₂O₃ or SiO₂ sol imparted different roughness geometry on the PET fabric surface. We observe surface structure of fish fin-like, particle-like and hybrid fin-particle for treated PET fabric with; Al₂O₃, SiO₂ and hybrid Al₂O₃–SiO₂ sol, under FESEM and AFM observations.AFM observations show the evolution of roughness (Ra) dimension of different surface structures with the order of: SiO₂ < Al₂O₃ < Al₂O₃–SiO₂ (Ra = 31, 63 and 273 nm). We believe that the disparity of the surface geometries lead into different surface WCA. FTIR spectra of Hybrid Al₂O₃–SiO₂ shows additional peak at 902, 850, 557, and 408 cm⁻¹ which can be ascribed to the hybridization structure.     

Synthesis,characterization, and catalytic activity in the <Emphasis Type="Italic">n</Emphasis>-heptane conversion over Pt/In–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> sol–gel prepared catalysts

Platinum catalysts supported on indium-doped alumina were prepared by the sol–gel method. The method allows the incorporation of In³⁺ in the alumina network. The indium-doped alumina supports showed narrow pore size distribution (5.4–4.0 nm) and high specific surface areas (258–280 m²/g). The ²⁷Al NMR-MAS spectroscopy identified aluminum in tetrahedral, pentahedral, and octahedral coordination; however, the intensity of the signal assigned to aluminum in pentahedral coordination diminishes with the increase of the content of indium. Total acidity determined by ammonia thermodesorption diminishes strongly in Pt/In–Al₂O₃ catalysts, suggesting a selective deposit of platinum over the acid sites of the support. The effect of the support in the platinum catalytic activity was evaluated in the n-heptane dehydrocyclization reaction. The selectivity patterns for such reaction were modified substantially in the doped Pt/In–Al₂O₃ catalysts, in comparison with the Pt-In/Al₂O₃–I coimpregnated reference catalyst. As an important result, the formation of benzene was suppressed totally over the indium-doped alumina sol–gel supports with a high content (3 wt%) of indium.     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.     

Liquid-phase isobutane alkylation with butenes over aluminum chloride complexes synthesized in situ from activated aluminum and <Emphasis Type="Italic">tert</Emphasis>-butyl chloride

The liquid-phase interaction between isobutane and butenes at 303 K and 2.5–3.0 MPa has been investigated using activated aluminum (Al*)-tert-butyl chloride (TBC) model system (TBC: Al* = 0.35−4 mol/mol). It has been demonstrated by attenuated total reflection FT-IR (ATR-FT-IR) spectroscopy that the catalytically active aluminum chloride complexes forming in situ in the hydrocarbon medium vary in composition. Alkylation as such takes place at equimolar proportions of the reactants (TBC: Al* = 1: 1) and butenes feed 1mass flow rate of 5 h⁻¹ per gram of Al*. According to ATR-FT-IR data, the most abundant aluminum complexes resulting under these conditions are the AlCl₄⁻ and Al₂Cl₇⁻ ions and, probably, the molecular complex AlCl₃ · sec-C₄H₉Cl. In a fourfold excess of TBC over Al* at butenes mass feed rate of 2.5 h⁻¹, isobutane undergoes self-alkylation. In this case, the Al₂Cl₇⁻ ion is not detected and the most abundant complexes are AlCl₄⁻, Al₃Cl₁₀⁻ and the molecular species AlCl₃ · tert-C₄H₉Cl. It is hypothesized that the Al₂Cl₇⁻ ion plays the key role in the liquid-phase alkylation of isobutane with butenes.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Structural and Optical Properties of Sol-Gel Deposited Proton Conducting Ta2O5 Films

Proton conducting tantalum oxide films were deposited on ITO (Indium Tin Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prepared using Ta(OC₂H₅)₅ as a precursor. X-ray diffraction studies determined that the sol-gel films, heat treated at temperatures below 400°C, were amorphous. Films heat treated at higher temperatures were crystalline with the hexagonal δ-Ta₂O₅ structure. The solar transmission values (T _s ) of tantala films on glass generally range from 0.8–0.9, depending on thickness. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the UV-VIS-NIR regions. The refractive index values calculated at λ=550 nm increased fromn=1.78 to 1.97 with increasing heat treatment from 150 to 450°C. The films heat treated at different temperatures showed low absorption, with extinction coefficients of smaller thank=1×10⁻³ in the visible range. Impedance spectroscopic investigations performed on Ta₂O₅ films revealed that these films have a protonic conductivity of 3.2×10⁻⁴S/m. The films are suitable for proton conducting layers in electrochromic (EC) devices.