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排序方式: 共有813条查询结果,搜索用时 15 毫秒
71.
Ilona Visser Monique Klinkenberg Peter Hoos Hans-Gerd Janssen John van Duynhoven 《Analytica chimica acta》2009,654(1):40-44
The performance of many contemporary detergent products critically depends on polymers. Water-soluble polycarboxylates represent an important class of detergent polymers, and their quantitative assessment in detergent matrices stands as a considerable challenge. The presence of high levels of surfactants is a major complication, due to the strong tendency of surfactants to form micelles and to interact with the polymers. First, we addressed critical steps in the subsequent combined use of liquid extraction and off-line size exclusion chromatography-nuclear magnetic resonance (SEC-NMR) for identification and quantification of polycarboxylates in detergent products. Next, the different steps in the off-line SEC-NMR procedure were optimized with respect to precision and accuracy. This resulted in recoveries of more than 80% for maleic acid/acrylic acid copolymers; in detergent products a proportional bias of 30% is achieved. The method showed good precision with a relative standard deviation of within-laboratory reproducibility between 5% and 14%. 相似文献
73.
Heterogeneous photocatalysis is a recent discipline particularly well adapted to environmental problems since it operates
at room temperature by replacing catalyst’s thermo-activation by photo-activation (or replacing phonons by photons). In fine
chemistry, high initial selectivities (100%) are obtained in dry organic media in selective mild oxidation of gaseous or liquid
hydrocarbons. Similarly, 100% selectivities were obtained in sulfur-involving photocatalytic reactions, noted as “thio-photocatalysis”.
Environmental photocatalysis is active in water and air decontamination and can advantageously use the UV-A solar spectrum
for outside applications. 相似文献
74.
Jalal Ghilane Pascal Martin Hyacinthe Randriamahazaka Jean-Christophe Lacroix 《Electrochemistry communications》2010,12(2):246-249
Electrochemical oxidation of primary amine in ionic liquid media has been investigated. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Two primary amine compounds are used for this study; 4-nitrobenzylamine and 2-aminoethylferrocenylmethylether. The oxidation of the amino compounds in ionic liquid conduces to the modification of the electrode surface. The modified electrodes were characterized by cyclic voltammetry and XPS analysis. Both techniques support the presence of an organic layer strongly attached onto the electrode surface. The surface concentration of the attached group obtained in this media was found to be around 1 to 3 × 10?10 mol cm?2. The use of ionic liquid as media for the grafting leads to decrease of the surface concentration of the grafted layer; and the formation of less dense layer compared with classical solvent such as acetonitrile. 相似文献
75.
Luís Santos Pascal Martin Jalal Ghilane Pierre-Camille Lacaze Hyacinthe Randriamahazaka Luisa Maria Abrantes Jean-Christophe Lacroix 《Electrochemistry communications》2010,12(7):872-875
The electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) films from aqueous surfactant solution through a two-dimensional poly(styrene) (PS) template onto indium tin oxide (ITO) substrate has been investigated. The polymer grows in the interstitial spaces of the self-assembled PS spheres which were subsequently removed by dissolution in tetrahydrofuran (THF). Surface characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveals that two-dimensional nanoporous honeycomb PEDOT structures can easily be obtained by using PS spheres of different sizes. Gold electrodeposition onto the nanostructured PEDOT electrode was investigated and SEM images show preferential formation of nanoparticles (NP) on the wall and the rim of the PEDOT film but metal clusters inside the pores are also observed. 相似文献
76.
Ekaterina P. Nesterenko Pavel N. Nesterenko Damian Connolly Flavie Lacroix Brett Paull 《Journal of chromatography. A》2010,1217(14):2138-2146
A new method for the fixation of polymethacrylate monoliths within titanium tubing of up to 0.8 mm I.D. for use as a chromatographic column under elevated temperatures and pressures is described. The preparation of butyl methacrylate–ethylene dimethacrylate-based monolithic stationary phases with desired porous structures was achieved within titanium tubing with pre-oxidised internal walls. The oxidised titanium surface was subsequently silanised with 3-trimethoxysilylpropyl methacrylate resulting in tight bonding of butyl methacrylate porous monolith to the internal walls, providing stationary phase stability at column temperatures up to 110 °C and at operating column pressure drops of >28 MPa. The titanium housed monoliths exhibited a uniform and dense porous structure, which provided peak efficiencies of up to 59,000 theoretical plates per meter when evaluated for the separation of small molecules in reversed-phase mode, under optimal conditions (achieved at 15 μL/min and temperature of 110 °C for naphthalene with a retention factor, k = 0.58). The developed column was applied to the reversed-phase isocratic separation of a text mixture of pesticides. 相似文献
77.
Fluorescence has recently been applied to the analysis of the molecular organization state of the polyene antibiotic amphotericin
B (AmB) in solution or in lipid membranes. The polyene chain of AmB monomer gives rise to two fluorescence emissions; S1(21Ag) → S0(11Ag) between 500 and 700 nm, S2(11Bu) → S0(11Ag) between 400 and 500 nm. However, Raman scattering might interfere with the S2 → S0 emission fluorescence due to the weak fluorescence quantum yield and close proximity to the exciting lines. In fact, we show
here that a change in the excitation wavelength results in a shift of three emission bands, an effect which excludes their
assignment to fluorescence. These bands originate from the water Raman at 3382 cm-1and AmB resonance Raman at 1556 and 1153 cm-1. As a consequence, some former conclusions on the molecular organization state of AmB should be reconsidered. 相似文献
78.
We propose a mechanism for optical trapping of dark excitons by linearly polarized unabsorbed standing waves, with a potential depth of the order of a few meV. Since this trapping, based on carrier exchanges with virtual excitons coupled to unabsorbed photons, equally acts on bright and dark states, Bose-Einstein condensation of excitons--which occurs in dark states--must appear as dark spots in a cloud of bright excitons, at the trap potential minima, when the temperature decreases. 相似文献
79.
Y. Lacroix 《Israel Journal of Mathematics》2002,132(1):253-263
LetG denote the set of decreasingG: ℝ→ℝ withGэ1 on ]−∞,0], and ƒ
0
∞
G(t)dt⩽1. LetX be a compact metric space, andT: X→X a continuous map. Let μ denone aT-invariant ergodic probability measure onX, and assume (X, T, μ) to be aperiodic. LetU⊂X be such that μ(U)>0. Let τ
U
(x)=inf{k⩾1:T
k
xεU}, and defineG
U
(t)=1/u(U)u({xεU:u(U)τU(x)>t),tεℝ We prove that for μ-a.e.x∈X, there exists a sequence (U
n
)
n≥1
of neighbourhoods ofx such that {x}=∩
n
U
n
, and for anyG ∈G, there exists a subsequence (n
k
)
k≥1
withG
U
n
k
↑U weakly.
We also construct a uniquely ergodic Toeplitz flowO(x
∞,S, μ), the orbit closure of a Toeplitz sequencex
∞, such that the above conclusion still holds, with moreover the requirement that eachU
n
be a cylinder set.
In memory of Anzelm Iwanik 相似文献
80.