[en] We found that the reactivity of Al-trifluoroacetoxydiisobutylalane (DIBAO₂CCF₃) is much stronger than that of Al-acetoxydiisobutylalane (DIBAOAc) toward carbonyl compounds: these results indicate that the strong electron-with rawing fluorine substituent in acetoxy group increases the acidity of the reagent and makes it stronger. From these experimental backgrounds, we designed the fluorinated methanesulfonyl derivative, Al-trifluromethane-sulfonyldiisobutylalane (DIBAO₃SCF₃), and applied to the reduction of epoxides. This communication described the reactivity and regioselectivity of DIBAO₃SCF₃ in the reaction of epoxides, and compares with those of DIBAO₃SCH₃. DIBAO₃SCF₃ can be readily prepared by a simple reaction of diisobutylaluminum hydride (DIBAH) with an equivalent of trifluoromethanesulfonic acid in Et₂O at 0 .deg. C

[en] Various microporous materials such as activated carbons, nano-tubes, synthetic micro-porous carbons as well as metal organic framework materials are being considered for hydrogen storage applications by means of physical adsorption. To develop materials of practical significance for hydrogen storage it is important to understand the relationships between pore sizes, adsorption energies and adsorption capacities. The pore size distribution (PSD) characterization is traditionally obtained from the analysis of nitrogen adsorption isotherms measured at 77 K. However, a portion of the pores accessible to H₂ may not be accessible to N₂ at this temperature. Therefore, it was recently proposed to use the DFT analysis of H₂ adsorption isotherms to characterize pore structure of materials considered for hydrogen storage applications [1]. In present work, adsorption isotherms of H₂ and N₂ at cryogenic temperatures are used for the characterization of carbon materials. Adsorption measurements were performed with Autosorb 1 MP [Quantachrome Instruments, Boynton Beach, Florida, USA]. As an example, Fig 1 compares PSDs calculated for the activated carbon sample (F400, Calgon Carbon) using combined H₂ and N₂ data, and using N₂ isotherm only. The nitrogen derived PSD does not include certain amount of micro-pores which are accessible to H₂ but not to N₂ molecules. Obviously, the difference in the calculated PSDs by the two methods will depend on the actual content of small micro-pores in a given sample. Carbon adsorption properties can also be characterized by the isosteric heat of adsorption, Qst, related to the adsorption energy and dependent on the carbon pore/surface structure. Fig 2 shows Qst data calculated using the Clausius-Clapeyron equation from H₂ isotherms measured at 77 K and 87 K for the carbon molecular sieve CMS 5A (Takeda), oxidized single wall nano-tubes (SWNT) [2], and graphitized carbon black (Supelco). The Qst values decrease with increasing pore sizes. The highest Qst is observed for the CMS sample having micropores sizes of about 5 A. The SWNT sample shows a lower Qst due to its relatively wide PSD [2], and the non-porous carbon black is characterized by the lowest Qst values. The Qst values calculated from H₂ adsorption isotherms measured at cryogenic temperatures below 1 atmosphere can be used to predict/estimate H₂ adsorption at ambient temperatures under high pressures. Fig 3 shows the H₂ adsorption isotherm on the SWNT sample calculated for 298 K from the low pressure and low temperature (77, 87 K) data using the Clausius-Clapeyron equation and assuming the temperature independence of the Qst values. A good agreement with high-pressure experimental data [3] is observed. Predictions using DFT model will also be discussed during presentation. [1] J. Jagiello, M. Thommes, Carbon 42, 1227, 2004. [2] A. Anson, J. Jagiello, J. B. Parra, M.L. Sanjuan, A. M. Benito, W. K. Maser, M. T. Martinez, J. Phys. Chem. B, 108, 15820, 2004. [3] A. Anson, M. Banham, J. Jagiello, M. A. Callejas, A. M. Benito, W. K. Maser, M. A. Zuttel, P. Sudan, M. T. Martinez, Nanotechnology, 15, 1503, 2004. (authors)

[en] Analyses of adsorption equilibriums were carried out with the hydrogen adsorption data on Multi-walled Carbon Nano-tubes (MWCNTs) and AX-21. Principles of thermodynamic equilibrium in each adsorption equilibrium state were applied to a lattice theory based model for determining the maximum surface concentration, adsorption potential well and the molecular interaction among hydrogen molecules. Results show that the interaction energies are nearly linear with the surface concentration, but the variation tendency is different between those in MWCNTs and AX-21. Comparison of the temperature dependence of the interaction energies on both adsorbents reveals a much complicated interaction mechanism in MWCNTs-hydrogen adsorption system. (authors)

[en] The search for cost effective adsorbents for large scale gas separation, storage and transport constitutes a present day strategic issue in the energy sector, propelled mainly by the potential use of hydrogen as an energy vector in a sustainable (and cleaner) energy scenario. Both, activated carbons and carbon based nano-structured materials have been proposed as potential candidates for reversible hydrogen storage in cryogenically cooled vessels. For that purpose, surface modification so as to enhance the gas solid interaction energy is desirable. We report on hydrogen adsorption on microporous (active) carbons which have been partially oxidised with nitric acid and ammonium persulfate. From the corresponding hydrogen adsorption isotherms (Fig. 1) an isosteric heat of about 3 kJ mol^-1 was derived. This value is in agreement with that of about 3 to 4 kJ mol^-1 obtained by quantum chemical calculations on the interaction between the hydrogen molecule and simple model systems (Fig. 2) of both, hydroxyl and carboxyl groups. Further research is in progress with a view to further increases the gas solid interaction energy. However, the values so far obtained are significantly larger than the liquefaction enthalpy of hydrogen: 0.90 kJ mol^-1; and this is relevant to both, hydrogen separation from gas mixtures and cryogenic hydrogen storage. (authors)

[en] This Full Paper focuses on the preparation of single-walled or multi-walled carbon nano-tube solutions with regioregular poly(3-hexyl-thiophene) (P3HT) and a fullerene derivative 1-(3-methoxy-carbonyl)propyl-1-phenyl[6,6]C₆₁ (PCBM) using a high dissolution and concentration method to exactly control the ratio of carbon nano-tubes (CNTs) to the P3HT/PCBM mixture and disperse the CNTs homogeneously throughout the matrix. The CNT/P3HT/PCBM composites are deposed using a spin-coating technique and characterized by absorption and fluorescence spectroscopy and by atomic force microscopy to underline the structure and the charge transfer between the CNTs and P3HT. The performance of photovoltaic devices obtained using these composites as a photoactive layer mainly show an increase of the short circuit current and a slight decrease of the open circuit voltage which generally leads to an improvement of the solar cell performances to an optimum CNT percentage. The best results are obtained with a P3HT/PCBM (1: 1) mixture with 0.1 wt % multi-walled carbon nano-tubes with an open circuit voltage (Voc) of 0.57 V, a current density at the short-circuit (I_sc) of 9.3 mA.cm^-2 and a fill factor of 38.4 %, which leads to a power conversion efficiency of 2.0 % (irradiance of 100 mW.cm^-2 spectroscopically distributed following AM1.5). (authors)

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No abstract available

[en] A study of a core sample of maikop clays showed that in a homogeneous stratum of maikop clays in the western Kuban depression there is a considerable variation in the uranium content (from 0.2 to 11.9x10^-4%). The average uranium content of the clays investigated is 4.7x10^-4%. The average content of Csub(org) for the clay samples investigated is 1.36% (Clark value 0.8%). When the data for the U and Csub(org) content of maikop clays were compared, a good correlation was found between these components (γ=0.82). This dependence is well in agreement with the data in the literature. The material presented and considered in the article permits the following conclusions: 1. A geochemical link is shown between uranium and the components of the dispersed organic substance in the clays of the maikop deposits of the western Kuban depression; 2. A direct correlative link is established between uranium and the Csub(org) of alcohol-benzol bitumoid DSBB (A) as a result of the presence of asfaltenes - polycyclic compounds where the uranium is in the form of a metallo-organic complex; 3. No direct correlational dependence is established between uranium and the alcohol-benzol bitumoid DSBB (S). Uranium was determined by the luminescence method, Csub(org) by the gasometric method with a Wirtz-Strohlein burette; the alcohol-benzol bitumoid DSBB (A) was extracted with chloroform and alcohol-benzol consecutively, and DSBB (S) with alcohol-benzol. (E.G.)

[en] An efficient method of hydrogen storage in nano-porous carbons is its reversible sorption by electrochemical decomposition of a KOH water solution [1-3] according to the following equation: C + xH₂O + xe^- → (CH_x) + xOH^- where (CH_x) stands for the hydrogen inserted into the nano-porous carbon during charging and oxidized during discharging. Although various carbon materials have been investigated as hydrogen adsorbents, the information about the storage mechanism as well as the nature of the hydrogen/carbon interaction is still not sufficient. In order to extend the understanding of the process, carbon samples charged electrochemically were investigated by temperature programmed desorption (TPD). The nature of the hydrogen/carbon interaction was studied by electrochemical analysis at different temperatures. The TPD experiments consist of heating the samples from room temperature to 950 C and of quantitative analysis by on-line mass spectrometry, the di-hydrogen evolved from the carbon material. Fig 1 shows the desorption rate of hydrogen during the TPD experiment carried out on an activated carbon cloth loaded at -500 mA/g during 12 hours. The first peak below 300 C corresponds to the desorption of hydrogen fixed on the carbon surface during the charging process. The shape and the position of this peak suggests that this gas is released from sites of different and relatively high energies. The second hydrogen peak results from the reaction between the carbon material and KOH as already mentioned in literature [4]. Carbon materials were also loaded at -500 mA/g during different times (3, 6, 12 and 24 hours), and then analysed by TPD, showing that the intensity of the peak below 300 C increases with the charging time. Hence TPD gives the direct proof that hydrogen is really stored in nano-porous carbons by this electrochemical process. Moreover, the position of the desorption peaks demonstrates that at least a part of hydrogen presents stronger interactions than in the state of physisorption. In order to confirm the latter interpretation, galvano-static cycling and cyclic voltammetry experiments were realized in 6 mol.L^-1' KOH at various temperatures ranging from 20 to 60 C. The results obtained show that, as temperature increases, both cathodic and anodic processes are accelerated (Fig. 2) by reducing the kinetic barriers, and in consequence the hydrogen uptake efficiency is enhanced. On the basis of the electrochemical data, an Arrhenius plot was created, and the activation energy related to the hydrogen reaction was estimated. [1] K. Jurewicz, E. Frackowiak, F. Beguin, Electrochem Solid State Lett, 4, A27, 2001; [2] K. Jurewicz, E. Frackowiak, F. Beguin, Appl Phys A, 78, 981, 2004; [3] C. Vix-Guterl, E. Frackowiak, K. Jurewicz, M. Friebe, J. Parmentier, F. Beguin, Carbon, 43, 1293, 2005; [4] M.A. Lillo-Rodenas, J. Juan-Juan, D. Cazorla-Amoros, A. Linares-Solano, Carbon, 42, 1365, 2004. (authors)

[en] The paper presents investigations on the carbonaceous substances encountered in uranium deposits of a certain type. A set of methods (IR spectroscopy, ultimate analysis and others) was used to examine the various types of carbonaceous compounds, their composition, structure and geochemistry, and their role in the formation of uranium concentrations. All the carbonaceous substances are divided into two main groups according to their spacial distribution: those syngenetic to the ore-containing sediments; and epigenetic materials introduced into them as a result of the development of an ascending carbon-bitumen process. A considerable similarity was found between the compositions and properties of forms that are known to have no genetic relation to each other, while carbonaceous formations related by a common origin and belonging to the same group are represented by several modifications with different internal structures and compositons. All the carbonaceous compounds of the syngenetic group occur in a random relationships to the uranium mineralization. Nevertheless, the presence of syngenetic carbonaceous substances assists the formation of rich concentrations of uranium. The appearance of epigenetic carbonaceous substances (bitumens) is generally more closely spacially related to zones of development of uranium mineralization. The maximum concentrations of uranium are typical for hard insoluble bitumens. Among the soluble bitumens, the carbonaceous substances - bitumen S - bound in epigenetic materials, are most enriched in uranium (up to px10^-3%). The role of the bitumens differs in the formation of displaced and primary uranium ores. In the first case, the significance of the bitumens, seems to lie in the reduction of the redox potential of the infiltrated uranium-bearing waters. In the second case, it is possible that a co-migration of uranium and certain types of carbonaceous substance (bitumen S, hard bitumen) took place in reducing (by iron) solutions). (author)