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排序方式: 共有75条查询结果,搜索用时 15 毫秒
31.
32.
Marcos Malta Guy Louarn Nicolas Errien Roberto M. Torresi 《Electrochemistry communications》2003,5(12):1011-1015
This contribution describes the synthesis of a hybrid nanocomposite constituted by vanadium oxide/polyaniline (PAni) with an interesting fibrilar morphology. Nanofibers can be obtained as main reaction products of nanocomposite V2O5/PAni and hexadecylamine after hydrothermal treatment. In general, nanocomposite nanofibers present a typical length varying from 1 to 10 μm and a width varying from 15 to 400 nm. Electrochemical experiments have shown a specific capacity of about 150 A h kg−1 during the 10 initials cycles, revealing a promissory material for utilization as cathode for ion-Li batteries. 相似文献
33.
Fulgêncio F de Oliveira FC Windmöller D Brito HF Malta OL de Sá GF Magalhães WF Machado JC 《Physical chemistry chemical physics : PCCP》2012,14(28):9996-10007
Positronium formation in the bimary molecular solid solutions Tb(1-x)Eu(x) (dpm)(3) (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the (5)D(4) Tb(iii) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism. 相似文献
34.
In this article we apply a model, based on the combined effect of a polarizable chemical environment (the Pseudo-Multipolar Field) and the mixing between J-levels, to study the 5D0→7F0 intensity of the Eu3+ ion in the {(C4H9)4N}3Y(NCS)6 host. Good agreement is found between theory and experiment. The results are discussed. 相似文献
35.
P. E. S. De Oliveira L. M. Conserva C. A. De Simone M. A. Pereira V. R. S. Malta D. O. Imbroisi 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(12):o900-o902
X‐ray diffraction studies carried out on single crystals of the monomeric, viz. 5,6‐dimethoxy‐2H‐furo[2,3‐h][1]benzopyran‐2‐one, C13H10O5, and dimeric, viz. 5,5′,6,6′‐tetramethoxy‐3,3′,4,4′‐tetrahydro‐2H,2′H‐3,3′:4,4′‐bi(furo[2,3‐h][1]benzopyran)‐2,2′‐dione, C26H20O10, forms of pimpinellin have revealed that, following cyclodimerization, the carbonyl groups are head‐to‐head with respect to one another. In the monomer, the heterocyclic ring is planar, but it exhibits a twisted‐boat conformation in the dimer. Both the monomer and the dimer interact through C—H⋯O interactions. 相似文献
36.
37.
Dr. Israel P. Assunção Dr. Albano N. Carneiro Neto Prof. Renaldo T. Moura Jr. Dr. Cássio C. S. Pedroso Dr. Ivan G. N. Silva Prof. Maria C. F. C. Felinto Prof. Ercules E. S. Teotonio Prof. Oscar L. Malta Prof. Hermi F. Brito 《Chemphyschem》2019,20(15):1931-1940
The odd–even effect in luminescent [Eu2(L)3(H2O)x]⋅y(H2O) complexes with aliphatic dicarboxylate ligands (L: OXA, MAL, SUC, GLU, ADP, PIM, SUB, AZL, SEB, UND, and DOD, where x=2–6 and y=0–4), prepared by the precipitation method, was observed for the first time in lanthanide compounds. The final dehydration temperatures of the Eu3+ complexes show a zigzag pattern as a function of the carbon chain length of the dicarboxylate ligands, leading to the so-called odd-even effect. The FTIR data confirm the ligand–metal coordination via the mixed mode of bridge–chelate coordination, except for the Eu3+-oxalate complex. XRD results indicate that the highly crystalline materials belong to the monoclinic system. The odd–even effect on the 4 f–4 f luminescence intensity parameters (Ω2 and Ω4) is explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom model. In this method, the long-range polarizabilities ( ) were simulated by a ghost atom located at the middle of each ligand chain. The values of were estimated using the localized molecular orbital approach. The emission intrinsic quantum yield ( ) of the Eu3+ complexes also presented an the odd-even effect, successfully explained in terms of the zigzag behavior shown by the Ω2 and Ω4 intensity parameters. Luminescence quenching due to water molecules in the first coordination sphere is also discussed and rationalized. 相似文献
38.
Rute A. S. Ferreira Mariela Nolasco Ana C. Roma Ricardo L. Longo Oscar L. Malta Luis D. Carlos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(38):12130-12139
In many EuIII‐based materials, the presence of an intermediate energy level, such as ligand‐to‐metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the 5D0 state, mainly at near‐resonance (large transfer rates). We present results for the dependence of the 5D0 lifetime on the excitation wavelength for a wide class of EuIII‐based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β‐diketonate complexes, organic–inorganic hybrids, macro‐mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four‐ and three‐level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near‐resonant non‐radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for TbIII/CeIII. Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized. 相似文献
39.
Itamara F. Leite Anna Priscilla S. Soares Laura H. Carvalho Claudia M. O. Raposo Oscar M. L. Malta Suédina M. L. Silva 《Journal of Thermal Analysis and Calorimetry》2010,100(2):563-569
Pristine and purified Argel sodium bentonites were organically modified with quaternary ammonium and phosphonium surfactants
by ion exchange reaction in order to investigate the effect of the chemical identity of the surfactant and of the clay purification
procedure in the intercalation process, final structure and thermal stability of organobentonites. The bentonites were characterized
by X-ray diffraction analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. The bentonite purification
treatment and, especially, the chemical structure of surfactant affected the thermal behavior of the organobentonites. The
phosphonium modified bentonites were thermally more stable than those modified with ammonium, particularly the purified bentonite.
These results seem to be promising regarding to the potential application of phosphonium modified Argel bentonites for the
melt processing preparation of nanocomposites with polymeric matrices requiring high processing temperatures. 相似文献
40.
Grazia Malta Simon A. Kondrat Simon J. Freakley David J. Morgan Emma K. Gibson Peter P. Wells Matteo Aramini Diego Gianolio Paul B. J. Thompson Peter Johnston Graham J. Hutchings 《Chemical science》2020,11(27):7040
The replacement of HgCl2/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl−, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C2H2 alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst. In situ chlorine and sulphur XAS shows a dynamic ligand environment around cationic Au single-sites during acetylene hydrochlorination. 相似文献