Suchergebnisse

Available online March 22, 2013.- El pdf del artículo es la versión post-print.-Supplementary data associated with this article can be found on pages 21-23. ; We here present an effective strategy to prepare enhanced composites using poly(vinyl alcohol) (PVA) and multiwalled carbon nanotubes (MWCNT). It contains two essential steps. First, the elaboration of homogeneous aqueous MWCNT dispersions and the selection of the most effective dispersing agent. In a sequential dispersion protocol for seven common dispersants, including surfactants and polymers, the dispersion quality and dispersion ability, independent of the intrinsic nature of the dispersing agent were established using zeta-potential and UV-Vis-spectroscopy. Second, the combination of the most effective dispersing agent, namely dodecylbenzenesulfonate (SDBS) with a polymer dispersant of high affinity towards the PVA matrix, namely polyvinylpyrrolidone (PVP). This resulted in homogeneous PVA-MWCNT composites with significantly improved glass transition temperature by up to 12 ºC as a function of the sequential order of dispersant addition. The presented dispersion strategy is straightforward and thus may provide a fast, reliable and general guide for fabricating nanotube composites with improved performance. ; This research was supported by Spanish Ministry of Science and Innovation (MICINN) under project MAT2010-15026, CSIC under project 201080E124, and the Government of Aragon (DGA) under project DGA-T66 CNN. The authors thank Nanocyl S.A. (Sambreville, Belgium) for providing nanotube samples. ; Peer reviewed

6 pages, 2 figures, 2 tables.- First published online 26 April, 2013 ; The synthesis of Pd nanoparticles (Pd-NPs) supported on multiwalled carbon nanotubes (MWCNTs) and the catalytic performance of the resulting material (Pd-NPs/MWCNTs) on hydrogenation reactions are presented. Facile preparation approaches based on the decomposition of Pd precursors in the presence of MWCNTs lead to homogeneous dispersions of supported Pd-NPs with average size of 4 nm and Pd loads about 12%. The catalytic performance of this material was evaluated in hydrogenation reactions of α,β-unsaturated ketones, alkenes, cyclic di-, tri-and tetraenes, aromatic compounds, terpenes and terpenoids, resulting in very high activity offering short reaction times, high conversion rates, notable selectivity, and acceptable recyclabitiliy under mild conditions. ; Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) under projects CTQ2011-22589 and MAT2010-15026, CSIC under project 201080E124, and the Regional Government of Aragon and the European Social Fund (ESF) under projects (DGA-PI086-08 and E-97, and DGA-ESF T66 CNN) is gratefully acknowledged. M. C. thanks MICINN and ESF for her Grant Nº BES- 2008-003503. ; Peer reviewed

Gold nanoparticles (AuNPs) with sizes between 3 and 10 nm were firmly supported on pristine multi-walled carbon nanotubes (MWCNT) in high yields by a facile linker-free deposition route using aqueous suspensions of pre-reduced gold precursors. For the first time, the resulting AuNP-MWCNT hybrid material was employed as catalyst for the hydrogenation of a series of substituted nitroarenes under mild reaction conditions. High catalytic activity with turnover frequencies (TOF) values up to 1200 h-1 were achieved accompanied by a remarkable chemoselectivity. Recyclability tests did neither reveal leaching nor changes in size or oxidation states of the AuNPs. The concomitant presence of Au0 and AuI accounts for both the superior catalytic performance and the high stability of the hybrid material. Preferential orientation of nitroarenes on the MWCNT surface due to π-π interactions coupled with coulombic contact of the nitro group to the AuNPs most likely explains the high chemoselectivity of the hybrid material, and further underlines the valuable role of MWCNTs for catalytic reactions. ; Financial support from Spanish MINECO and the European Regional Development Fund (projects MAT2010-15026, ENE2013-48816-C5-5-R and CTQ2011-22589), Spanish National Research Council CSIC (project 201080E124), and Regional Government of Aragon and the European Social Fund DGA-ESF (T66 Grupo Consolidado, E-97, and E-26) is gratefully acknowledged. ; Peer reviewed

Available online June 23, 2012.- El pdf del artículo es la versión post-print ; Composites of thermoplastic polyurethane (TPU) and ultra-thin graphite (UTG) with concentrations ranging from 0.5 wt.% to 3 wt.% were prepared using a solution compounding strategy. Substantial reinforcing effects with increased loadings are achieved. Compared to neat TPU, values for storage modulus and shear viscosity are enhanced by 300% and 150%, respectively, for UTG concentrations of 3 wt.%. Additionally, an enhancement of thermal properties is accomplished. The crystallization temperature and thermal stability increased by 30 C and 10 C, respectively, compared to neat TPU. Furthermore, the use of oxidized UTG (UTGO) with its added functional oxygen groups suggests the presence of chemical interactions between UTG and TPU, which additionally impact on the thermal properties of the corresponding composites. Controlling the oxidation degree, thus offers further possibilities to obtain composites with tailored properties. The presented approach is straightforward, leads to homogeneous TPU-UTG composites with improved materials properties and is especially suitable for commercial UTG materials and further up-scaled production. ; This research was supported by IMPIVA under project (IMIDIP/2010/58), Spanish Ministry of Science and Innovation (MICINN) under project MAT2010-15026, CSIC under project 201080E124, and the Government of Aragon (DGA) and the European Social Fund (ESF) under project DGA-ESF-T66 CNN. M. C. thanks MICINN and ESF for her grant nº BES-2008-003503. Authors thank Merquinsa S.L. (Barcelona, Spain) and AVANZARE S.L. (La Rioja, Spain) for kindly providing polyurethane and ultrathin graphite samples, respectively. ; Peer Reviewed

We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young's moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in * Corresponding author. Tel/Fax: +34 976 73-3977 / -3318. E-mail address: wmaser@icb.csic.es (W.K. Maser) 2 PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA-f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f- (PVA)GO loadings below 0.3 vol.%. ; The authors would like to acknowledge Science Foundation Ireland, (grant number 07/IN.7/I1772), Spanish Ministry of Science and Innovation (MICINN) under project MAT2010-15026, Spanish Research Council CSIC under project 201080E124 and the Government of Aragon (DGA) under Project DGA-T66 CNN. M.C. thanks MICINN for her PhD contract and funding for research stay at TCD under FPI Programme BES-2008-003503. ; Peer reviewed