Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

MoO<Subscript>2</Subscript>(acac)<Subscript>2</Subscript> supported on MCM-41: An efficient and reusable catalyst for alkene epoxidation with <Emphasis Type="Italic">tert</Emphasis>-BuOOH

A new heterogeneous catalyst prepared by immobilization of MO₂(acac)₂ on Mobil Catalytic Material, MCM-41, is reported. This catalyst, MoO₂(acac)₂-MCM-41, was successfully applied for efficient epoxidation of olefins with tert-BuOOH in 1,2-dichloroethane as solvent. The catalyst was characterized by elemental analysis, FT-IR, UV-Vis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). This catalyst can be reused several times without significant loss of its catalytic activity.     

Structure of the Cu(Salen) molecule Cuo<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> according to gas-phase electron diffraction data and quantum chemical calculations

In the framework of synchronous gas-phase electron diffraction and mass spectrometry experiment, the saturated vapor of N,N′-ethylenebis(salicylaldiminate) copper(II) CuO₂N₂C₁₆H₁₄ is studied at a temperature T 574(5) K. It is found that evaporation is congruent and the saturated vapor consists of monomeric molecules. Electron diffraction data are proved to correspond to the geometric model for the CuO₂N₂C₁₆H₁₄ molecule of C ₂ symmetry with an almost planar structure of the CuN₂O₂ coordination fragment and internuclear distances \(r_{h_1 } \)(Cu-O) = 1.917(13) Å and \(r_{h_1 } \)(Cu-N) = 1.931(15) Å. The stuctural parameters obtained are compared to those quantum chemically calculated and molecular parameters in crystals.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

Sol-gel processing of lead-free (Na,K)NbO<Subscript>3</Subscript> ferroelectric films

The sol-gel processing of lead-free (Na,K) NbO₃ ferroelectric films was studied. Sodium ethoxide (NaOC₂H₅) and potassium ethoxide (KOC₂H₅) were prepared by reacting solid Na and K with ethanol (99.7%) in a solvent of 2-methoxyethanol. 0.5-μm-thick (Na,K)NbO₃ thin films with orthorhombic perovskite structure were obtained by pyrolyzing at 400°C and annealing at 800–900°C. The films had relatively dense and uniform microstructure with grain size of about 50 nm, whose ferroelectricity was proved by the P-E hysteresis loop measurement. It was found that excess K was effective to reduce the annealing temperature for the crystallization of sol-gel-derived (Na,K)NbO₃ thin films.     

Molecular structure of NiO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> from gas-phase electron diffraction and quantum chemical data

Gas-phase electron diffractometry was used to study the molecular structure of N,N′-ethylenebis(salicylaldiminato)nickel(II), NiO₂N₂C₁₆H₁₄, [hereinafter Ni(salen)] at 583(5) K. The molecule has C ₂ symmetry with a practically planar structure of the NiN₂O₂ coordination unit and with internuclear distances r _α (Ni-O) = 1.882(21) Å and r _α (Ni-N) = 1.889(22) Å. The results of B3LYP/CEP-31G molecular structure calculations are in good agreement with experimental data, whereas the RHF/CEP-31G method significantly overestimates the Ni-N internuclear distance and gives worse results for other structural parameters. According to 3LYP/CEP-31G calculations, the ¹ A low-spin state is 28 kJ/mole lower in energy than the ³ B high-spin state.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Sol–gel processing of IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> mixed metal oxides based on a hexachloroiridate precursor

Mixed IrO₂–TiO₂ oxides were prepared by the sol–gel method upon acid-catalysed hydrolysis of an iridium solution in ethanol mixed with titanium tetraethoxide in ethanol. The iridium solution was obtained by reaction of the sodium hexachloroiridate(IV) precursor in the presence of sodium ethoxide in ethanol. Gels were formed in all but the high-Ir samples. Analysis of the dried gels showed minority-phase enrichment at the surface and the presence of Ir(III), while microscopy showed evidence for dispersed iridium-containing nanoparticles (1–20 nm in diameter). XRD powder patterns of the calcined material showed peaks due to a small amount of crystalline NaCl impurity which could be removed by washing. This left amorphous phases, except in the Ir:Ti 3:2 case, which showed evidence for the presence of separate crystalline oxide phases: anatase, IrO₂ and Ti _x Ir_1−x O₂.     

ENDOR study of bis(acetylacetonato)oxovanadium (IV) in frozen liquid crystals

An ENDOR study of vanadyl bisacetylacetonate (VO(acac)₂) aligned in frozen nematic liquid cystals shows enhanced ENDOR signal intensities, which may aid in the interpretation of powder ENDOR spectra obtained from transition-metal complexes in isotropic glasses. The ENDOR spectra establish that VO(acac)₂ is present in the form of an adduct with the solvent molecules. The adduct formation may affect the alignment of the solute molecules in the liquid crystal.     

A new phosphor with flower-like structure and luminescent properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> long afterglow materials by sol–gel method

The flower-like phosphors of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ with high brightness and long afterglow were obtained by sol–gel method. X-ray diffraction pattern (XRD) shows that single-phased Sr₂MgSi₂O₇ phosphor is prepared by sol–gel method under 1250 °C. Scanning electron microscope (SEM) indicates that the phosphor consists of nano-sized whiskers which are detected for the first time in Eu²⁺ and Dy³⁺ co-doped long-lasting phosphorescence silicates. Furthermore, the investigation on the mechanism indicates that the internal structure and gas, liquid and solid phase effect play important roles in the formation of flower-like Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ nanostructure. Finally, the optical properties of flower-like Sr₂MgSi₂O₇ nanostructure have been characterized by photoluminescence (PL) spectra.     

Ammonia gas sensor based on a spinel semiconductor,Co<Subscript>0.8</Subscript>Ni<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanomaterial

Thick film of nanocrystalline Co_0.8Ni_0.2Fe₂O₄ was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co_0.8Ni_0.2Fe₂O₄. XRD of Co_0.8Ni_0.2Fe₂O₄ revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H₂S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and LiCoO<Subscript>2</Subscript> composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn₂O₄/(1 ? x) LiCoO₂(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn₂O₄ and LiCoO₂ partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ～100 mAh/g.     

Phase relations in the CoO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system in subsolidus area

Thermal properties of Co₂FeV₃O₁₁ have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V₂O₅–Fe₂O₃ system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.     

FTIR-ATR <Emphasis Type="Italic">in situ</Emphasis> observation on the efflorescence and deliquescence processes of Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> aerosols

The efflorescence and deliquescence processes of Mg(NO₃)₂ aerosol particles deposited on ZnSe substrate have been investigated through in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) technique at the molecular level. At relative humidity (RH) of ∼3%, Mg(NO₃)₂ particles existed as amorphous states. The amorphous Mg(NO₃)₂ particles were transformed into crystalline Mg(NO₃)₂ · nH₂O (n ≤ 5) with slight increasing of RH. Thermodynamically stable Mg(NO₃)₂·6H₂O crystals were gradually formed on the particle surface and started to be dissolved at the saturation point (∼53% RH). At the same time, a continuous phase transition from Mg(NO₃)₂ · nH₂O (n≤5) to Mg(NO₃)₂·6H₂O occurred on the particle surface. This led the solid particles to completely deliquesce at 76% RH, which was much higher than the saturation point of 53% RH. In the efflorescence process, Mg(NO₃)₂ droplets entered into the supersaturated region due to the gradual evaporation of water. Finally, amorphous particles were formed when RH decreased below 5%. In the FTIR-ATR spectra of the supersaturated Mg(NO₃)₂ droplets, the absorbance of the symmetric stretching vibration of NO ₃ ⁻ (v ₁- NO ₃ ⁻ ) clearly became stronger. It resulted from the continuous formation of solvent share ion pairs (SIPs), and even the contact ion pairs (CIPs) between Mg²⁺ and NO ₃ ⁻ . Supported by the Trans-Century Program Foundation for the Talents by the Ministry of Education of China, the National Natural Science Foundation of China (Grant Nos. 20073004, 20473012, and 20673010), the 111 Project (B07012), and the State Key Laboratory of Physical Chemistry for Solid Surface of Xiamen University     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

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.     

Sol-gel preparation and spectroscopic study of the pyrophanite MnTiO<Subscript>3</Subscript> nanoparticles

The nanosized xerogel of titanium dioxide (TiO₂) and manganese oxides (MnO₂, Mn₂O₃, Mn₃O₄) was prepared by the sol-gel method using manganese chloride (MnCl₂·4H₂O) and titanium isopropoxide (Ti(O-iPr)₄) as precursors in cetyltrimethylammonium bromide (CTAB)/ ethanol/H₂O/HCl micelle solutions, following the calcinations of the produced powders at difference temperatures. The nanostructure and phase composition of these nanoparticles were characterized with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The spectroscopic characterizations of these nanoparticles were also done with UV-Vis spectroscopy and laser Raman spectroscopy (LRS). XRD patterns show that the pyrophanite MnTiO₃ phase was formed at the calcinations temperature of 900°C. The TEM images show that the nanoparticles are almost spherical or slight ellipose and the sizes are 50 nm on average. The UV-Vis spectra show that the nanosized MnTiO₃ have significant absorption bands in the visible region. There are new absorption peaks of MnTiO₃ nanoparticles in LRS compared with the pure TiO₂ powder.