Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系光谱性质的研究

根据稀土离子能级的特点,对Ga2O3-La2O3-Yb2O3-Er2O3(HO2O3)体系的光谱性质进行了探讨,发现它们有二类发光性质:Stokes发光和反Stokes发光,研究了发光强度和发射波长与掺杂离子的依赖关系,观察到由能量的共振转移引起的荧光浓度猝灭现象,并取得了最大发光强度时的掺杂离子浓度和一些规律性结果.     

Excited carrier dynamics of alpha-Cr2O3/alpha-Fe2O3 core-shell nanostructures

In this work alpha-Cr(2)O(3)/alpha-Fe(2)O(3) core-shell polycrystalline nanostructures were synthesized by using alpha-Cr(2)O(3) nanoparticles as seed crystals during aqueous nucleation. The formation of alpha-Fe(2)O(3) polycrystallites on alpha-Cr(2)O(3) surfaces was confirmed by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray analysis. The excited-state relaxation dynamics of as-grown core-shell structures and "pure" alpha-Fe(2)O(3) particles of the same size were measured with femtosecond transient absorption spectroscopy. The results show the carrier lifetimes decay within a few picoseconds regardless of sample. This is likely due to fast recombination/trapping of carriers to defects and iron d-states.     

Synthesis and characterization of the open-framework barium bisphosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O

Following the strategy of using polyfunctional phosphonic acids for the synthesis of open-framework metal phosphonates, the phosphonocarboxylic acid (H2O3PCH2)2NCH2C6H4COOH was used in the hydrothermal synthesis of new Ba phosphonates. Its decomposition led to the first open-framework barium phosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O. The synthesis was also successfully performed using iminobis(methylphosphonic acid), (H2O3PCH2)2NH, as a starting material, and the synthesis was optimized to obtain as a pure material. The reaction setup as well as the pH are the dominant parameters, and only a diffusion-controlled reaction led to the desired compound. The crystal structure was solved from single-crystal data: monoclinic; C2/c; a=2328.7(2), b=1359.95(7), and c=718.62(6) pm; beta=98.732(10) degrees ; V=2249.5(3)x10(6) pm3; Z=4; R1=0.036; and wR2=0.072 (all data). The structure of [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O is built up from BaO8 and BaO10 polyhedra forming BaO chains and layers, respectively. These are connected to a three-dimensional metal-oxygen-metal framework with the iminobis(methylphosphonic acid) formally coating the inner walls of the pores. The one-dimensional pores (3.6x4 A) are filled with H2O molecules that can be thermally removed. Thermogravimetric investigations and temperature-dependent X-ray powder diffraction demonstrate the stability of the crystal structure up to 240 degrees C. The uptake of N,N-dimethylformamide and H2O by dehydrated samples is demonstrated. Furthermore, IR, Raman, and 31P magic-angle-spinning NMR data are also presented.     

Oxidative dehydrogenation of propane over V2O5/MoO3/Al2O3 and V2O5/Cr2O3/Al2O3: structural characterization and catalytic function

The structure and catalytic properties of binary dispersed oxide structures prepared by sequential deposition of VO(x) and MoO(x) or VO(x) and CrO(x) on Al(2)O(3) were examined using Raman and UV-visible spectroscopies, the dynamics of stoichiometric reduction in H(2), and the oxidative dehydrogenation of propane. VO(x) domains on Al(2)O(3) modified by an equivalent MoO(x) monolayer led to dispersed binary structures at all surface densities. MoO(x) layers led to higher reactivity for VO(x) domains present at low VO(x) surface densities by replacing V-O-Al structures with more reactive V-O-Mo species. At higher surface densities, V-O-V structures in prevalent polyvanadates were replaced with less reactive V-O-Mo, leading to lower reducibility and oxidative dehydrogenation rates. Raman, reduction, and UV-visible data indicate that polyvanadates predominant on Al(2)O(3) convert to dispersed binary oxide structures when MoO(x) is deposited before or after VO(x) deposition; these structures are less reducible and show higher UV-visible absorption energies than polyvanadate structures on Al(2)O(3). The deposition sequence in binary Mo-V catalysts did not lead to significant differences in structure or catalytic rates, suggesting that the two active oxide components become intimately mixed. The deposition of CrO(x) on Al(2)O(3) led to more reactive VO(x) domains than those deposited on pure Al(2)O(3) at similar VO(x) surface densities. At all surface densities, the replacement of V-O-Al or V-O-V structures with V-O-Cr increased the reducibility and catalytic reactivity of VO(x) domains; it also led to higher propene selectivities via the selective inhibition of secondary C(3)H(6) combustion pathways, prevalent in VO(x)-Al(2)O(3), and of C(3)H(8) combustion routes that lead to low alkene selectivities on CrO(x)-Al(2)O(3). VO(x) and CrO(x) mix significantly during synthesis or thermal treatment to form CrVO(4) domains. The deposition sequence, however, influences catalytic selectivities and reduction rates, suggesting the retention of some of the component deposited last as unmixed domains exposed at catalyst surfaces. These findings suggest that the reduction and catalytic properties of active VO(x) domains can be modified significantly by the formation of binary dispersed structures. VO(x)-CrO(x) structures, in particular, lead to higher oxidative dehydrogenation rates and selectivities than do VO(x) domains present at similar surface densities on pure Al(2)O(3) supports.     

Y2O3和Nd2O3介孔薄膜的制备与表征

以聚乙烯合丁烯-嵌-聚氧乙烯嵌段共聚物(PHB-PEO)作模板, 采用蒸发诱导自组装方法, 分别制备了Y2O3和Nd2O3介孔薄膜. 用小角、广角X射线衍射和透射电子显微镜对薄膜样品在不同的热处理阶段进行了表征. 结果表明, 所制备的Y2O3和Nd2O3薄膜样品呈现一种大孔径(平均孔径分别约为11.5和12.5 nm)、有序的立方扭曲球形孔排列、稳定于450 ℃并具有部分晶态孔壁结构的介孔薄膜材料.     

Antimony dispersion and phase evolution in the Sb2O3-Fe2O3 system

This paper studies the antimony spreading and segregation that occurred along with the oxidation and solid-state reactions in the Fe2O3-Sb2O3 system. XRD, SEM, TG-DSC and particularly XPS were employed for characterizations. Sb2O4 and FeSbO4 are the only new phases detected. The formation of FeSbO4 is a more exothermic but slower reaction than oxidation of Sb2O3. A mechanical grinding of Sb2O3 and Fe2O3 leads to a significant dispersion of Sb2O3 possibly because of its low hardness. Dispersion of reference Sb2O4 in this way is negligible. During the heating of a mixture of Sb2O3 and Fe2O3 with an atomic ratio of Sb/Fe = 0.5 at 200-1000 degrees C in ambient air, the thermal spreading of Sb2O3 onto Fe2O3 increases with increasing temperature until Sb2O3 is oxidized into Sb2O4. The surface atomic ratio of Sb/Fe measured by XPS, R(Sb/Fe), reaches a maximum around 400 degrees C. The complete oxidation of Sb2O3 leads to a decrease in R(Sb/Fe) because of poorer dispersibility of Sb2O4. The formation of FeSbO4 starting at ca. 800 degrees C causes a further decrease in R(Sb/Fe), but the R(Sb/Fe) is still 3.2 times the nominal bulk Sb/Fe ratio when the Sb2O4 is completely transformed into FeSbO4.     

H2O2-Na2S2O3反应对pH和反应物起始浓度比的依赖性

在H2O2-Na2S2O3反应体系中，pH值和[H2O2]0/[Na2S2O3]0对反应产物的浓度大小起着关键作用.本文通过考察这两种因素对反应产物的影响，以及对反应机理的模拟，得出了pH值和氧化剂与还原剂浓度比影响反应产物浓度的一般规律.结果表明：pH< 3时，反应主要生成单质硫， 3< pH< 6时， 较为稳定，提高pH和[H2O2]0/[Na2S2O3]0有利于SO42-生成，在中性或弱碱性溶液中S(Ⅳ)(HSO42-或SO32-)物质浓度出现峰值.     

Polynuclear vanadium complexes from thermal decomposition of [V3O(O2CPh)6(H2O)3]Cl

Solid-state decomposition of [V3O(O2CPh)6(H2O)3]Cl at 300 degrees C followed by alcoholysis of the product gives the new vanadium complexes [V6O6(PhCO2)6(CH3O)6(CH3OH)3] (1), [V6O6(PhCO2)6(C2H5O)6(C2H5OH)3] (2), [V6O6(PhCO2)6(C3H7O)6(C3H7OH)3] (3), [V6O6(PhCO2)6(C4H9O)6(C4H9OH)3] (4) and [V4O4(OCH3)6(O2CPh)2(HOCH3)2] (5). Complexes 2, 3 and 5 have been crystallographically characterised. DC magnetic susceptibility studies on complex shows antiferromagnetic coupling leading to a S = 0 spin ground state.     

Formation of heterodimer nanocrystals: UO2/In2O3 and FePt/In2O3

This Article reports a mechanistic study on the formation of colloidal UO(2)/In(2)O(3) and FePt/In(2)O(3) heterodimer nanocrystals. These dimer nanocrystals were synthesized via the growth of In(2)O(3) as the epitaxial material onto the seed nanocrystals of UO(2) or FePt. The resulting dimer nanocrystals were characterized using X-ray powder diffraction (XRD), energy dispersion spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy, and high-resolution TEM (HRTEM). The results from XRD and HRTEM clearly show that lattice strains exist in both of these dimer nanocrystals. Interestingly, the lattice of In(2)O(3) expands in UO(2)/In(2)O(3) dimers, whereas FePt/In(2)O(3) dimers exhibit compressed In(2)O(3) lattices. Using HRTEM and nanocrystal structure simulations, we have identified the crystallographic orientation of the attachment of the two segments in these two types of dimers. An unconventional Miller index was introduced to describe the crystallographic orientation of these heterodimer nanocrystals. On the basis of the results herein as well as those from other researchers, we propose an empirical law for the determination of the crystallographic attachment orientation in heterodimers: instead of growth on the facet of the seed nanocrystals where lattice mismatch is minimized, the growth of an epitaxial material often chooses the crystal facets where the first atomic monolayer of this material has the strongest affinity for the seed nanocrystals.     

Calcium and strontium thio­sulfate,CaS2O3·6H2O and SrS2O3·5H2O

In contrast to former morphological studies, the results presented here show that calcium(II) thio­sulfate hexahydrate, CaS₂O₃·6H₂O, crystallizes centrosymmetrically in the pinacoidal class (point group ). The structure is characterized by chains, parallel to [100], of alternating S₂O₃ and Ca(H₂O)₆O₂ groups sharing common O atoms. The composition of each chain link is [Ca(H₂O)₆(S₂O₃)]. The geometry is analysed and compared in detail with the structural features of monoclinic strontium(II) thio­sulfate pentahydrate, SrS₂O₃·5H₂O, which forms layers, parallel to (100), of alternating S₂O₃ and Sr(H₂O)₄O₅ groups connected via common O atoms and O–O edges. Each layer contains [Sr(H₂O)₃O(S₂O₃)]_∞ as the unique repeat unit.     

Effect of Bi2O3 addition on electron paramagnetic resonance, optical absorption, and conductivity in vanadyl-doped Li2O-K2O-Bi2O3-B2O3 glasses

Glasses with composition 15Li(2)O-15K(2)O-xBi(2)O(3)-(65 - x)-B(2)O(3)/5V(2)O(5) (3 ≤ x ≤ 15) have been prepared by the conventional melt quench technique. The electron paramagnetic resonance spectra of VO(2+) in these glasses have been recorded in the X-band frequency (≈9.3 GHz) at room temperature. The spin Hamiltonian parameters and covalency rates were evaluated. It was found that the V(4+) ions exist as vanadyl (VO(2+)) ions and are in an octahedral coordination with a tetragonal compression. The covalency rates (1 - α(2)) and (1 - γ(2)) indicate moderate covalency for the σ- and π-bonds. It was observed that the spin-Hamiltonian parameters depend slightly on the relative concentration of Bi(2)O(3). The optical properties of this glass system are studied from the optical absorption spectra recorded in the wavelength range 200-800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed transitions have been determined using available theories. The direct current electrical conductivity, σ, has been measured in the temperature range 373-573 K. The conductivity decreases with the increase in Bi(2)O(3) concentration. This has been discussed in terms of the decrease in the number of mobile ions and their mobility. An attempt is made to correlate the EPR, optical, and electrical results and to find the effect of Bi(2)O(3) content on these parameters.     

Time-resolved spectroscopic behavior of Fe2O3 and ZnFe2O4 nanocrystals

Using nanosecond (ns) and femtosecond (fs) time-resolved absorption spectroscopies (pump-probe technique), the carrier dynamics in transition metal oxide nanocrystals of alpha-Fe2O3 and ZnFe2O4 was studied during the photolysis process. For Fe2O3 and ZnFe2O4 nanocrystals, the fs measurements detect similar profiles of a positive nonlinear absorption in their capped nanocrystals, whereas much weak signals in the naked particles. In the nanosecond measurements Fe2O3 and ZnFe2O4 nanocrystals show obvious excitation-power dependent absorption properties and at the low pump power they show weak photobleaching, but at high pump power they produce positive nonlinear absorptions. For Fe2O3 nanocrystals, the threshold power of negative absorption (bleach) to positive absorption increases with reducing size, whereas for the ZnFe2O4 samples, the threshold powers reach minimum at a critical size of 11 nm, grow for both the bigger and the smaller nanocrystals. These results reflect the influences of their microscopic magnetic couplings and carrier correlation on biexciton absorption in Fe2O3 and ZnFe2O4 nanocrystals. All the results indicate that the time resolved photoabsorption techniques are useful to study the microscopic spin interactions and carrier correlations in transition metal oxide nanocrystals.     

Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O: a layered cadmium phosphonate with reversible dehydration/hydration properties

In a recent systematic study on the influence of the reaction temperature on the structure formation in the system CdCl2/H(HO3PCH2)2NH-CH2C6H4-COOH (H5L) /NaOH, [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O was obtained as a microcrystalline compound. We have now been able to elucidate the structure from single-crystal data: triclinic, P; a=5.4503(9), b=12.880(2), and c=16.417(3) A; alpha=67.841(6) degrees, beta=80.633(6) degrees, gamma=87.688(8) degrees, V=1052.9(3) A3; Z=1; R1=0.1143, R2=0.2108 (all data); 0.0705, 0.1823 ((I>2sigmaI)). The structure of [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O is built up of cadmium phosphonate layers connected by water-mediated hydrogen bonds between aryl-carboxylic acid groups and water molecules coordinated to Cd2+ ions of adjacent layers (C-OH...H2O...H2O-Cd2+). The title compound was characterized by IR spectroscopy and energy dispersive X-ray, elemental, and thermogravimetric analyses. Furthermore, temperature-dependent X-ray diffraction data are presented. [Cd3(H2O)3((O3PCH2)2NH-CH2C6H4-COOH)2].11H2O can be reversibly dehydrated, and mechanical stress and grinding in the presence of water leads to the intercalation of additional water molecules.     

Molecular and supramolecular features of oxo-peroxovanadium complexes containing O3N, O2N2 and ON3 donor sets

The complexes [VO(O2)Hbpa]+ (1a), [VO(O2)bpa] (1b, Hbpa = bis(picolyl)-beta-alanine), [VO(O2)heida]- (2, H2heida =N-(2-hydroxyethyl)iminodiacetic acid), [VO(O2)(3OH-pic)2]- (3a), [VO(O2)(3OH-pic)2]-/[V(O2)2(3OH-pic)2]- (3b, 3OH-pic = 3-hydroxypicolinic acid), [VO(O2)(3OH-pa)2] (6, 3OH-pa = 3-hydroxypicolylamide), [VO2(3OH-pic)2]- (4), [VO(tBuO2)(3OH-pic)2] (5) and [VO(tBuO2)(3OH-pa)2]2+ (7) have been characterised. The structures of 21a[ClO4].1b.2.25H2O, K.2H2O, [NH4].H2O and [nBu4]3b are reported. Supramolecular patterns arise from intermolecular hydrogen bonds, the relevance of which for the peroxo/hydroperoxo intermediates in oxo transfer reactions catalysed by vanadate-dependent haloperoxidases is addressed. Specific solution patterns have been analysed by 51V and 17O NMR.     

Photolysis of pure solid O3 and O2 films at 193 nm

We studied quantitatively the photochemistry of solid O(3) and O(2) films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O(3), but a small amount of ozone remained in the film at high fluence. Photolysis of pure O(2) produced O(3) in an amount that increased with photon fluence to a stationary level. For both O(2) and O(3) films, the O(3):O(2) ratio at large fluences is ～0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed to the increased photodissociation of O(2) due to photoabsorption by O(2) dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, Φ(O(3)) = 0.24 ± 0.06, and quantum yields for destruction of O(3) and O(2) in their parent solids, Φ(-O(3)) = 1.0 ± 0.2 and Φ(-O(2)) = 0.36 ± 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 ± 0.1 for O(3) fragments and 0.88 ± 0.03 for oxygen atoms from O(2) dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O(2) vs. O(3) to be 0.1-0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.     

Luminescent lanthanide selenites and tellurites decorated by MoO4 tetrahedra or MoO6 octahedra: Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12

Solid state reactions of lanthanide oxide, MoO3 and SeO2 (or TeO2) at high temperature in an evacuated quartz tube lead to four new Ln-Mo-Se(Te)-O quaternary phases with four different types of structures, namely, Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12. The structure of Nd2MoSe2O10 features a 3D architecture built by the intergrowth of the Nd-Se-O layers with the Nd-Mo-O layers. The structure of Gd2MoSe3O12 contains a 3D network of gadolinium selenite with the MoO6 octahedra occupying the cavities of the structure. The structure of La2MoTe3O12 features a 3D network of La2(Te3O8)2+ with the tunnels along the a axis occupied by the MoO4 tetrahedra. Nd2MoTe3O12 features a 2D layer built by the lanthanide ions interconnected by tellurite groups and ditellurite groups, with the MoO4 tetrahedra as the interlayer pendant groups. Room temperature and low temperature luminescent studies indicate that Nd2MoSe2O10 and Nd2MoTe3O12 exhibit strong luminescence in the near-IR region.     

Thermal Decomposition of CF3C(O)O2NO2, CClF2C(O)O2NO2, CCl2FC(O)O2NO2, and CCl3C(O)O2NO2

Haloacetyl, peroxynitrates are intermediates in the atmospheric degradation of a number of haloethanes. In this work, thermal decomposition rate constants of CF₃C(O)O₂NO₂, CClF₂C(O)O₂NO₂, CCl₂FC(O)O₂NO₂, and CCl₃C(O)O₂NO₂ have been determined in a temperature controlled 420 l reaction chamber. Peroxynitrates (RO₂NO₂) were prepared in situ by photolysis of RH/Cl₂/O₂/NO₂/N₂ mixtures (R = CF₃CO, CClF₂CO, CCl₂FCO, and CCl₃CO). Thermal decomposition was initiated by addition of NO, and relative RO₂NO₂ concentrations were measured as a function of time by long-path IR absorption using an FTIR spectrometer. First-order decomposition rate constants were determined at atmospheric pressure (M = N₂) as a function of temperature and, in the case of CF₃C(O)O₂NO₂ and CCl₃C(O)O₂NO₂, also as a function of total pressure. Extrapolation of the measured rate constants to the temperatures and pressures of the upper troposphere yields thermal lifetimes of several thousands of years for all of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitrates may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rates. Results on the thermal decomposition of CClF₂CH₂O₂NO₂ and CCl₂FCH₂O₂NO₂ are also reported, showing that the atmospheric lifetimes of these peroxynitrates are very short in the lower troposphere and increase to a maximum of several days close to the tropopause. The ratio of the rate constants for the reactions of CF₃C(O)O₂ radicals with NO₂ and NO was determined to be 0.64 ± 0.13 (2σ) at 315 K and a total pressure of 1000 mbar (M = N₂). © 1994 John Wiley & Sons, Inc.     

In situ ATR-IR study of prochiral 2-methyl-2-pentenoic acid adsorption on Al2O3 and Pd/Al2O3

Adsorption and desorption of trans-2-methyl-2-pentenoic acid (MPeA) in dichloromethane (CH(2)Cl(2)) were investigated by using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. A liquid flow-through spectroscopic cell allowed for high quality spectra to be obtained from deposited thin films of Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) on a ZnSe internal reflection element. The MPeA molecules adsorb on both Al(2)O(3) and Pd surfaces molecularly and dissociatively under the concentration range examined (2-16 mM). In the case of molecular adsorption, both monomer (ν(C=O) ~ 1720 cm(-1)) and dimer (ν(C=O) ~ 1685 cm(-1)) species are observed to adsorb, with the relative amount of monomer to dimer dependent on the surface and the liquid phase acid concentration. In the case of dissociative adsorption, the acid adsorbs predominantly in a bridged bidentate configuration, as adjudged by the ca. 150-220 cm(-1) separation between asymmetric and symmetric vibrational bands. All of these species are found to be strongly adsorbed on both Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) surfaces, even under pure solvent flow after adsorption.     

Photoelectrochemical properties of Fe2O3-Nb2O5 films prepared by sol-gel method

Fe2O3-Nb2O5 coating films of various Nb/(Fe + Nb) mole ratios were prepared on nesa silica glass substrates from Fe(NO3)3.9H2O - NbCl5 - CH3(CH2)2CH2OH - CH3COOH solutions by the sol-gel method. The photoanodic properties were studied in a three-electrode cell with an aqueous buffer solution of pH = 7 as the supporting electrolyte. The crystalline phases identified were alpha-Fe2O3 (Nb/(Fe + Nb) = 0), alpha-Fe2O3 + FeNbO4 (Nb/(Fe + Nb) = 0.25), FeNbO4 (Nb/(Fe + Nb) = 0.5), FeNbO4 + Nb2O5 (Nb/(Fe + Nb) = 0.75), and Nb2O5 (Nb/(Fe + Nb) = 1). When the Nb/(Fe + Nb) mole ratio increased from 0 to 0.25, the crystalline phases changed from alpha-Fe2O3 to alpha-Fe2O3 + FeNbO4, the photoanodic current under white light illumination increased, and the photoanodic current under monochromatized light illumination increased in both visible and ultraviolet regions. When the Nb/(Fe + Nb) ratio increased over 0.25, the crystalline phases changed to FeNbO4, FeNbO4 + Nb2O5, or Nb2O5, and the photoanodic current decreased. The sample consisting of alpha-Fe2O3 and FeNbO4 (Nb/(Fe + Nb) = 0.25) exhibited photoresponse extending to 600 nm and an IPCE of 18% at a wavelength of 325 nm.