排序方式: 共有41条查询结果,搜索用时 703 毫秒
21.
A. Calleja S. Ricart X. Palmer R. F. Luccas T. Puig X. Obradors 《Journal of Sol-Gel Science and Technology》2010,53(2):347-352
Uncontrolled water content in non-aqueous precursor solutions can be a source of irreproducibility in thin film performance
through changes in the gel network. Towards gaining control on the solution properties, water determination in metalorganic
solutions of YBCO-TFA has been studied by the Karl Fischer titration in a volumetric-type unit. However, oxidizing cations
usually present when preparing functional oxides by chemical solution routes severely interfere in the Karl Fischer analysis.
In the case of YBCO-TFA, cupric ions in the initial solution oxidize the iodide produced in the Karl Fischer reaction back
to iodine, which in turn feeds the titration reaction and consumes more water, causing a negative error in the analysis, which
can be as large as 70%. However, such chemical interference of cupric salts can be modelled and quantified. A corrected Karl
Fischer methodology is proposed for accurately measuring water content in YBCO-TFA solutions, which could be potentially extended
to other precursor solutions containing oxidant cations. 相似文献
22.
Alberto Rold��n Josep M. Ricart Francesc Illas 《Theoretical chemistry accounts》2011,128(4-6):675-681
Density functional theory calculations using a plane-wave basis set and a generalized gradient approach exchange-correlation potential have been carried out to study the dissociation of molecular oxygen by Au nanoparticles and its dependence with particle size. The analysis of the energy related data shows that the reactivity is dominated by the energy barrier height from adsorbed O2 to the dissociated state and by the stability of molecular oxygen on the nanoparticle. The energy barrier is found to be only slightly dependent on the particles size where large variations are found for the adsorption energy of the O2 molecule on the different nanoparticles. A careful analysis of the electronic structure shows that the driving force for O2 adsorption by these nanoparticles is the existence of a clear gap between occupied and unoccupied states for the naked particle. This allows accommodating bonding states with O2 below the Fermi level resulting in a strong interaction. On the contrary, the Au nanoparticles with a more metallic electronic structure have necessarily to accommodate bonding and antibonding states below the Fermi level with a concomitant weaker interaction with O2. 相似文献
23.
J.A. Garrido F. Illas J.M. Ricart J. Rubio 《Journal of Electroanalytical Chemistry》1985,196(2):387-395
Ab initio calculations have been carried out for the interactions of atomic hydrogen with Ag5 cluster models, simulating the adsorption on the one-fold and four-fold sites of the (100) and (110) silver surfaces. It is found that one-layer cluster models lead to unreasonable results as a consequence of their high instability. Chemisorption on the one-fold site is found to be the preferred one. This results is easily interpreted on the basis of symmetry properties of the higher occupied molecular orbitals. 相似文献
24.
Preparation of potential insect antijuvenile hormone agents with polyoxyethyl and glycosyl groups at C-8 position of the 2-H-chromene ring of precocenes is described. 相似文献
25.
Monitoring the effect of chemicals on biological communities. The biofilm as an interface 总被引:1,自引:0,他引:1
Sabater S Guasch H Ricart M Romaní A Vidal G Klünder C Schmitt-Jansen M 《Analytical and bioanalytical chemistry》2007,387(4):1425-1434
Biofilms can be regarded as early warning systems for detection of the effects of toxicants on aquatic systems, because they
have been successfully used for detection of other environmental stressors (e.g. pH, salinity, organic pollution). A variety
of methods is used for detection of the effects of toxicants by use of biofilms. The methods range from structurally-based
to functionally-based, and from in vitro-based to systemic approaches. Physiological approaches may be appropriate for detection
of acute effects. Among these methods, photosynthesis is more related to the effect of toxicants affecting algal communities,
directly or indirectly, and extracellular enzyme activity is less specific. Selecting one or the other may depend on the suspected
direct effect of the toxicant. Integrated studies have revealed the relevance of toxicants to top-down or bottom-up regulation
of the biofilm community. Persistent or chronic effects should affect other biofilm indicators, for example growth or biomass-related
factors (e.g. chlorophyll), or community composition. Among these, community composition might better reflect the effects
of the toxicant(s), because this may cause a shift from a sensitive to a progressively tolerant community. Community composition-based
approaches do not usually adequately reflect cause–effect relationships and require complementary analysis of properties affected
in the short-term, for example physiological properties. The current array of methods available must be wisely combined to
disentangle the effects of chemicals on biofilms, and whether these effects are transient or persistent, to successfully translate
the chemical action of toxicants into the effect they might have on the river ecosystem. 相似文献
26.
We have used the ab initio cluster model approach to study the dependence of the CO stretching frequency on CO surface coverage. We have also investigated the relative importance of the various factors that can affect the position of the CO stretching band as coverage increases. Two effects can change the CO stretching frequency: the adsorbate–adsorbate dipole coupling, which is a purely physical effect, and the changes in the 2π* CO molecular orbitals, due to the different chemical environment at higher coverages. From our vibrational analysis, we conclude that CO–CO dipole coupling is the main cause of the upward shift of the CO stretching band when the CO coverage is increased. The population of the 2π* CO molecular orbitals does not change at any coverage within the region considered. We have also estimated the 12CO–13CO dipole coupling, which previous studies have assumed to be weak. Our results demonstrate that the 12CO–13CO dipole coupling is indeed weak compared with the 12CO–12CO dipole coupling. At a CO surface coverage of 0.5 monolayers (ML), we have calculated a band shift of 40 cm−1 to higher frequency. However, we should point out that when one 12CO molecule is surrounded by a 13CO environment, the 12CO stretching band shifts 10 cm−1 upwards. We have also computed the heat of adsorption of CO on Pt{100}-(1×1) as a function of CO coverage. The initial heat of adsorption is calculated to be about 192 kJ mol−1 and then drops to 180 kJ mol−1 at 0.5 ML. These results agree quite well with recent calorimetric measurements. Besides that, we have estimated that the CO–CO interaction energy at 0.5 ML is repulsive and has a value of 5 kJ mol−1. 相似文献
27.
Josep M. Ricart Marie P. Habas Anna Clotet Daniel Curulla Francesc Illas 《Surface science》2000,460(1-3):170-181
The adsorption of CO2 on the clean and potassium-precovered Pt(111) surface has been studied by means of the cluster model approach within the hybrid B3LYP density functional theory-based method. On the clean surface, CO2 is undistorted and weakly bound. The equilibrium position of this physisorbed species appears at a rather large distance from the surface. However, when coadsorbed K atoms are included in the model, a chemisorbed, bent CO2 species on top of a surface Pt atom is found. The presence of the coadsorbed K is found to be necessary to promote CO2 chemisorption and activation, the key step in activating the CO2 molecule being a direct interaction with the coadsorbate. In addition, the calculated vibrational frequencies for this chemisorbed species are in agreement with available experimental data. 相似文献
28.
Soler R Salabert J Sebastián RM Vallribera A Roma N Ricart S Molins E 《Chemical communications (Cambridge, England)》2011,47(10):2889-2891
Artificial hydrophobic surfaces have a great potential in a wide range of industrial applications owing to their self-cleaning, anti-fogging and anti-biofouling properties. A family of polyfluorinated reactive azo dyes has been prepared and some of them easily modified and grafted on cotton fabric and glass surfaces obtaining new coloured hydrophobic materials. 相似文献
29.
Charge Polarization at a Au–TiC Interface and the Generation of Highly Active and Selective Catalysts for the Low‐Temperature Water–Gas Shift Reaction
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Dr. José A. Rodriguez Dr. Pedro J. Ramírez Gian Giacomo Asara Dr. Francesc Viñes Prof. Jaime Evans Dr. Ping Liu Prof. Josep M. Ricart Prof. Francesc Illas 《Angewandte Chemie (International ed. in English)》2014,53(42):11270-11274
Au atoms in contact with TiC(001) undergo significant charge polarization. Strong metal–support interactions make Au/TiC(001) an excellent catalyst for the low‐temperature water–gas shift (WGS), with turnover frequencies orders of magnitude larger than those observed for conventional metal/oxide catalysts. DFT calculations indicate that the WGS reaction follows an associative mechanism with HOCO as a key intermediate. 相似文献
30.
Alberto Roldán Francesc Viñes Francesc Illas Josep Manel Ricart Konstantin M. Neyman 《Theoretical chemistry accounts》2008,120(4-6):565-573
Density functional plane-wave calculations have been carried out for series of Cu n ,Ag n and Au n particles containing up to 146 (Cu, Ag) and 225 (Au) atoms. Full geometry optimization has been performed for all particles starting from the structures created by cuts from the bulk. In line with previous studies, calculated average nearest-neighbour distances and cohesive energies of the particles linearly depend on such size-derived parameters as the average coordination number of metal atoms and the inverse of the mean particle radius, respectively. Rather accurate linear extrapolation of the observables under scrutiny to the bulk values has been achieved. However, we show that the scalability for particles made of various elements of the same d10s1 electron configuration differs, e.g. for bond lengths in Au n species it is noticeably less perfect than that for Cu n and Ag n ones. Implications of encountered structural peculiarities of the nanoparticles for their reactivity are outlined. 相似文献