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排序方式: 共有189条查询结果,搜索用时 62 毫秒
51.
M. Deepa 《Applied Surface Science》2005,252(5):1568-1580
A significant influence of microstructure on the electrochromic and electrochemical performance characteristics of tungsten oxide (WO3) films potentiostatically electrodeposited from a peroxopolytungstic acid (PPTA) sol has been evaluated as a function of annealing temperature. Powerful probes like X-ray diffractometry (XRD), transmission electron microscopy (TEM), UV-vis spectrophotometry, multiple step chronoamperometry and cyclic voltammetry have been employed for the thin film characterization. The as-deposited and the film annealed at 60 °C are composed of nanosized grains with a dominant amorphous phase, as well as open structure which ensues from a nanoporous matrix. This ensures a greater number of electroactive sites and a higher reaction area thereby manifesting in electrochromic responses superior to that of the films annealed at higher temperatures. The films annealed at temperatures ≥250 °C are characterized by a prominent triclinic crystalline structure and a hexagonal phase co-exists at temperatures ≥400 °C. The deleterious effect on the electrochromic properties of the film with annealing is ascribed to the loss of porosity, densification and the increasing crystallinity and grain size. Amongst all films under investigation, the film annealed at 60 °C exhibits a high transmission modulation (ΔT ∼ 68%) and coloration efficiency (η ∼ 77.6 cm2 C−1) at λ = 632.8 nm, charge storage capacity (Qins ∼ 21 mC cm−2), diffusion coefficient (6.08 × 10−10 cm2 s−1), fast color-bleach kinetics (tc ∼ 275 s and tb ∼ 12.5 s) and good electrochemical activity, as well as reversibility for the lithium insertion-extraction process upon cycling. The remarkable potential, which the film annealed at 60 °C has, for practical “smart window” applications has been demonstrated. 相似文献
52.
Paramagnetic copper(II) complexes of the type [Cu(PPh3)(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H2L1), 2‐hydroxy‐1‐naphthaldehyde (H2L2), o‐hydroxyacetophenone (H2L3) and o‐vanillin (H2L4) with monomeric metal precursor [CuCl2(PPh3)2]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)? Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)? Cu(I),in the range ?0.29 to ?0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide as co‐oxidant. The formation of high valent CuIV?O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
53.
We report a new series of polyurethane–oligo(phenylenevinylene) (OPV) random copolymers and their self‐assembled nanomaterials such as pores, vesicles, and luminescent spheres. The polymers were synthesized through melt transurethane process by reacting a hydroxyl‐functionalized OPV with diurethane monomer and diol under solvent‐free and nonisocyanate conditions. The amount of OPV was varied up to 50 mol % in the feed to incorporate various amounts of π‐conjugated segments in the polyurethane backbone. The π‐conjugated segmented polymers were subjected to solvent induced self‐organization in THF or THF+water to produce variety of morphologies ranging from pores (500 nm to 1 μm) to spheres (100 nm to 2 μm). Upon shining 370‐nm light, the dark solid nanospheres of the copolymers transformed into blue luminescent nanoballs under fluorescence microscope. The mechanistic aspects of the self‐organization process were studied using solution FTIR and photophysical techniques such as absorption and emission to trace the factors which control the morphology. FTIR studies revealed that the hydrogen bonding plays a significant role in the copolymers with lower amount of OPV units. Time resolved fluorescent decay measurements of copolymers revealed that molecular aggregation via π‐conjugated segments play a major role in the samples with higher OPV content in the random block polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 46: 5897–5915, 2008 相似文献
54.
In this paper, we establish the influence of pump power on the tuning characteristics of a filterless erbium-doped fiber laser,
operating in the L band. Tunable action is achieved with the control of intra cavity loss. The explicit dependence of tunability
on the average inversion levels is brought out. The shift in the lower limit of tuning range and the non-linear dependence
of lasing wavelength on the intra cavity loss are analytically deduced using the gain spectra and experimentally interpreted
using amplified spontaneous emission spectra. Continuous tunability is achieved with the careful control of pump power.
PACS 42.55.Wb; 42.60.Da; 42.55.-f 相似文献
55.
Pogrebnyakov AV Redwing JM Raghavan S Vaithyanathan V Schlom DG Xu SY Li Q Tenne DA Soukiassian A Xi XX Johannes MD Kasinathan D Pickett WE Wu JS Spence JC 《Physical review letters》2004,93(14):147006
We report a systematic increase of the superconducting transition temperature T(c) with a biaxial tensile strain in MgB2 films to well beyond the bulk value. The tensile strain increases with the MgB2 film thickness, caused primarily by the coalescence of initially nucleated discrete islands (the Volmer-Weber growth mode.) The T(c) increase was observed in epitaxial films on SiC and sapphire substrates, although the T(c) values were different for the two substrates due to different lattice parameters and thermal expansion coefficients. We identified, by first-principles calculations, the underlying mechanism for the T(c) increase to be the softening of the bond-stretching E(2g) phonon mode, and we confirmed this conclusion by Raman scattering measurements. The result suggests that the E(2g) phonon softening is a possible avenue to achieve even higher T(c) in MgB2-related material systems. 相似文献
56.
57.
Ramaraj Deepa Rathinasamy Gandhidasan Vairathevar Sivasamy Vasantha 《Research on Chemical Intermediates》2018,44(11):6917-6931
Research on Chemical Intermediates - A simple fluorescence sensor for selective detection of L-Tryptophan (Trp) was developed by isolation of naturally occurring flavone Eupatorin... 相似文献
58.
59.
Michael M. Konnick Brian G. Hashiguchi Deepa Devarajan Nicholas C. Boaz T. Brent Gunnoe John T. Groves Niles Gunsalus Daniel H. Ess Roy A. Periana 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(39):10658-10662
Direct partial oxidation of methane, ethane, and propane to their respective trifluoroacetate esters is achieved by a homogeneous hypervalent iodine(III) complex in non‐superacidic (trifluoroacetic acid) solvent. The reaction is highly selective for ester formation (>99 %). In the case of ethane, greater than 0.5 M EtTFA can be achieved. Preliminary kinetic analysis and density functional calculations support a nonradical electrophilic CH activation and iodine alkyl functionalization mechanism. 相似文献
60.
Dr. Palraj Kasinathan Dr. Charlotte Lang Dr. Sambhu Radhakrishnan Dr. Josefine Schnee Cécile D'Haese Dr. Eric Breynaert Prof. Johan A. Martens Prof. Eric M. Gaigneaux Prof. Alain M. Jonas Dr. Antony E. Fernandes 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6753-6762
Solid acid catalysts are central in our chemical industry and are major players in the valorization of bioresources. However, there is still a need to develop solid acid catalysts with enhanced acid strength and improved, or tunable, physicochemical profile to enhance the efficiency and sustainability of chemical processes. Here, a modular approach to tune the acid strength and surface polarity of silica-supported sulfonic acid catalysts, based on a versatile copper-catalyzed azide–alkyne cycloaddition (CuAAC)-based anchoring scheme, is presented. The CuAAC-formed triazole link was used to enhance the activity of the grafted sulfonic acids and to pair the acid sites with secondary hydrophobic functions. The beneficial effects of both the triazolium link and the paired hydrophobic site, as well as the optimal positioning of the sulfonic moiety on the triazole ring, are discussed in model esterification reactions. 相似文献