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Murcia A.B.,Instituto Universitario Of Materiales | Geng J.,University of Bolton
Journal of Nanoscience and Nanotechnology | Year: 2013

We report a study of synthesising air-stable, nearly monodispersed bimetallic colloids of Co/Pd and Fe/Mo of varying compositions as active catalysts for the growth of carbon nanotubes. Using these catalysts we have investigated the effects of catalyst and substrate on the carbon nanostructures formed in a plasma-enhanced chemical vapour deposition (PECVD) process. We will show how it is possible to assess the influence of both the catalyst and the support on the controlled growth of carbon nanotube and nanofiber arrays. The importance of the composition of the catalytic nuclei will be put into perspective with other results from the literature. Furthermore, the influence of other synthetic parameters such as the nature of the nanoparticle catalysts will also be analysed and discussed in detail. Copyright © 2013 American Scientific Publishers All rights reserved.

Vidal L.,Instituto Universitario Of Materiales | Chisvert A.,University of Valencia | Canals A.,Instituto Universitario Of Materiales | Salvador A.,University of Valencia
Talanta | Year: 2010

A user-friendly and inexpensive ionic liquid-based single-drop microextraction (IL-SDME) procedure has been developed to preconcentrate trace amounts of six typical UV filters extensively used in cosmetic products (i.e., 2-hydroxy-4-methoxybenzophenone, isoamyl 4-methoxycinnamate, 3-(4′-methylbenzylidene)camphor, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate, 2-ethylhexyl 4-dimethylaminobenzoate and 2-ethylhexyl 4-methoxycinnamate) from surface water samples prior to analysis by liquid chromatography-ultraviolet spectrophotometry detection (LC-UV). A two-stage multivariate optimization approach was developed by means of a Plackett-Burman design for screening and selecting the significant variables involved in the SDME procedure, which were later optimized by means of a circumscribed central composite design. The studied variables were drop volume, sample volume, agitation speed, ionic strength, extraction time and ethanol quantity. Owing to particularities, ionic liquid type and pH of the sample were optimized separately. Under optimized experimental conditions (i.e., 10 μL of 1-hexyl-3-methylimidazolium hexafluorophosphate, 20 mL of sample containing 1% (v/v) ethanol and NaCl free adjusted to pH 2, 37 min extraction time and 1300 rpm agitation speed) enrichment factors up to ca. 100-fold were obtained depending on the target analyte. The method gave good levels of repeatability with relative standard deviations varying between 2.8 and 8.8% (n = 6). Limits of detection were found in the low μg L-1 range, varying between 0.06 and 3.0 μg L-1 depending on the target analyte. Recovery studies from different types of surface water samples collected during the winter period, which were analysed and confirmed free of all target analytes, ranged between 92 and 115%, showing that the matrix had a negligible effect upon extraction. Finally, the proposed method was applied to the analysis of different water samples (taken from two beaches, two swimming pools and a river) collected during the summer period. © 2009 Elsevier B.V. All rights reserved.

Montagnaro F.,University of Naples Federico II | Silvestre-Albero A.,Instituto Universitario Of Materiales | Silvestre-Albero J.,Instituto Universitario Of Materiales | Rodriguez-Reinoso F.,Instituto Universitario Of Materiales | And 3 more authors.
Microporous and Mesoporous Materials | Year: 2015

Fixed bed CO2 adsorption tests were carried out in model flue-gas streams onto two commercial activated carbons, namely Filtrasorb 400 and Nuchar RGC30, at 303 K, 323 K and 353 K. Thermodynamic adsorption results highlighted that the presence of a narrower micropore size distribution with a prevailing contribution of very small pore diameters, observed for Filtrasorb 400, is a key factor in determining a higher CO2 capture capacity, mostly at low temperature. These experimental evidences were also corroborated by the higher value of the isosteric heat derived for Filtrasorb 400, testifying stronger interactions with CO2 molecules with respect to Nuchar RGC30. Dynamic adsorption results on the investigated sorbents highlighted the important role played by both a greater contribution of mesopores and the presence of wider micropores for Nuchar RGC30 in establishing faster capture kinetics with respect to Filtrasorb 400, in particular at 303 K. Furthermore, the modeling analysis of 15% CO2 breakthrough curves allowed identifying intraparticle diffusion as the rate-determining step of the process. © 2014 Elsevier Inc. All rights reserved.

Barbosa O.,Industrial University of Santander | Torres R.,Industrial University of Santander | Ortiz C.,Industrial University of Santander | Berenguer-Murcia A.,Instituto Universitario Of Materiales | And 2 more authors.
Biomacromolecules | Year: 2013

A heterofunctional support for enzyme immobilization may be defined as that which possesses several distinct functionalities on its surface able to interact with a protein. We will focus on those supports in which a final covalent attachment between the enzyme and the support is achieved. Heterofunctionality sometimes has been featured in very old immobilization techniques, even though in many instances it has been overlooked, giving rise to some misunderstandings. In this respect, glutaraldehyde-activated supports are the oldest multifunctional supports. Their matrix has primary amino groups, the hydrophobic glutaraldehyde chain, and can covalently react with the primary amino groups of the enzyme. Thus, immobilization may start (first event of the immobilization) via different causes and may involve different positions of the enzyme surface depending on the activation degree and immobilization conditions. Other "classical" heterofunctional supports are epoxy commercial supports consisting of reactive covalent epoxy groups on a hydrophobic matrix. Immobilization is performed at high ionic strength to permit protein adsorption, so that covalent attachment may take place at a later stage. Starting from these old immobilization techniques, tailor-made heterofunctional supports have been designed to permit a stricter control of the enzyme immobilization process. The requirement is to find conditions where the main covalent reactive moieties may have very low reactivity toward the enzyme. In this Review we will discuss the suitable properties of the groups able to give the covalent attachment (intending a multipoint covalent attachment), and the groups able to produce the first enzyme adsorption on the support. Prospects, limitations, and likely pathways for the evolution (e.g., coupling of site-directed mutagenesis and thiol heterofunctional supports of enzyme immobilization on heterofunctional supports) will be discussed in this Review. © 2013 American Chemical Society.

Balsamo M.,University of Naples Federico II | Rodriguez-Reinoso F.,Instituto Universitario Of Materiales | Montagnaro F.,University of Naples Federico II | Lancia A.,University of Naples Federico II | Erto A.,University of Naples Federico II
Industrial and Engineering Chemistry Research | Year: 2013

CO2 adsorption onto two particle size classes of the commercial activated carbon Filtrasorb 400, namely 600-900 μm (sample F600-900) and 900-1200 μm (sample F900-1200), was investigated at 293 K under model flue gas conditions in a fixed-bed column. Equilibrium adsorption capacity for a typical 15% CO2 postcombustion effluent was 0.7 mol kg-1 for both investigated adsorbents. In both cases, CO2 breakthrough curves showed a reduction of the characteristic breakpoint time and faster capture kinetics at higher pollutant concentration in the feed (in the range 1-15%). Dynamic adsorption data highlighted the important role played by wider micropores in determining a quicker adsorption process for finer particles. Mathematical modeling of the 15% CO2 breakthrough curve allowed identifying intraparticle diffusion as the limiting step of the adsorption process. Numerical analysis provided values of the intraparticle mass-transfer resistances equal to 1.7 and 3.3 s for F600-900 and F900-1200, respectively. © 2013 American Chemical Society.

Rodrigues R.C.,Federal University of Rio Grande do Sul | Barbosa O.,Industrial University of Santander | Ortiz C.,Industrial University of Santander | Berenguer-Murcia A.,Instituto Universitario Of Materiales | And 2 more authors.
RSC Advances | Year: 2014

Improvement of the features of an enzyme is in many instances a pre-requisite for the industrial implementation of these exceedingly interesting biocatalysts. To reach this goal, the researcher may utilize different tools. For example, amination of the enzyme surface produces an alteration of the isoelectric point of the protein along with its chemical reactivity (primary amino groups are the most widely used to obtain the reaction of the enzyme with surfaces, chemical modifiers, etc.) and even its "in vivo" behavior. This review will show some examples of chemical (mainly modifying the carboxylic groups using the carbodiimide route), physical (using polycationic polymers like polyethyleneimine) and genetic amination of the enzyme surface. Special emphasis will be put on cases where the amination is performed to improve subsequent protein modifications. Thus, amination has been used to increase the intensity of the enzyme/support multipoint covalent attachment, to improve the interaction with cation exchanger supports or polymers, or to promote the formation of crosslinkings (both intra-molecular and in the production of crosslinked enzyme aggregates). In other cases, amination has been used to directly modulate the enzyme properties (both in immobilized or free form). Amination of the enzyme surface may also pursue other goals not related to biocatalysis. For example, it has been used to improve the raising of antibodies against different compounds (both increasing the number of haptamers per enzyme and the immunogenicity of the composite) or the ability to penetrate cell membranes. Thus, amination may be a very powerful tool to improve the use of enzymes and proteins in many different areas and a great expansion of its usage may be expected in the near future. © the Partner Organisations 2014.

Leyva-Garcia S.,Instituto Universitario Of Materiales | Morallon E.,Instituto Universitario Of Materiales | Cazorla-Amoros D.,Instituto Universitario Of Materiales | Beguin F.,Poznan University of Technology | Lozano-Castello D.,Instituto Universitario Of Materiales
Carbon | Year: 2014

In situ Raman spectroscopy was exploited to analyze the interaction between carbon and hydrogen during electrochemical hydrogen storage at cathodic conditions. Two different activated carbons were used and characterized by different electrochemical techniques in two electrolytes (6 M KOH and 0.5 M Na2SO4). The in situ Raman spectra collected showed that, in addition to the D and G bands associated to the graphitic carbons, two bands appear simultaneously at about 1110 and 1500 cm-1 under cathodic conditions, and then they disappear when the potential increases to more positive values. This indicates that carbon-hydrogen bonds are formed reversibly in both electrolytes during cathodic conditions. Comparing the two activated carbons, it was confirmed that, in both electrolytes, the hydrogenation of carbon atoms is produced more easily for the sample with lower amount of surface oxygen groups. In KOH medium, for the two samples, the formation of carbon-hydrogen bonds proceeds at more positive potential with respect to the thermodynamic potential value for hydrogen evolution. Furthermore, changes in the shape of the D band (due to an intensity increase of the D1 band) during the formation of carbon-hydrogen bonds suggest that hydrogenation of the carbon atoms increases the number of edge planes. © 2013 Elsevier Ltd. All rights reserved.

Casco M.E.,Instituto Universitario Of Materiales | Morelos-Gomez A.,Shinshu University | Vega-Diaz S.M.,Shinshu University | Cruz-Silva R.,Shinshu University | And 9 more authors.
Journal of CO2 Utilization | Year: 2014

CO2 adsorption has been measured in different types of graphitic nanostructures (MWCNTs, acid treated MWCNTs, graphene nanoribbons and pure graphene) in order to evaluate the effect of the different defective regions/conformations in the adsorption process, i.e., sp3 hybridized carbon, curved regions, edge defects, etc. This analysis has been performed both in pure carbon and nitrogen-doped nanostructures in order to monitor the effect of surface functional groups on surface created after using different treatments (i.e., acid treatment and thermal expansion of the MWCNTs), and study their adsorption properties. Interestingly, the presence of exposed defective regions in the acid treated nanostructures (e.g., uncapped nanotubes) gives rise to an improvement in the amount of CO2 adsorbed; the adsorption process being completely reversible. For N-doped nanostructures, the adsorption capacity is further enhanced when compared to the pure carbon nanotubes after the tubes were unzipped. The larger proportion of defect sites and curved regions together with the presence of stronger adsorbent-adsorbate interactions, through the nitrogen surface groups, explains their larger adsorption capacity. © 2014 Elsevier Ltd. All rights reserved.

Silvestre-Albero J.,Instituto Universitario Of Materiales | Silvestre-Albero A.,Instituto Universitario Of Materiales | Rodriguez-Reinoso F.,Instituto Universitario Of Materiales | Thommes M.,Quantachrome Instruments
Carbon | Year: 2012

In order to get more insight into the characterization of nanoporous carbons by gas adsorption, the use of different probe molecules has been compared. A series of activated carbons with ranging porosity (burn-off) have been prepared from olive stones using CO 2 as activating agent and characterized using nitrogen and argon adsorption at low temperature (77.4 K for N 2 and 87.3 K for Ar) together with CO 2 adsorption at 273 K and immersion calorimetry into liquids of different molecular dimensions. Experimental results show that argon adsorption in narrow carbon micropores takes place at a higher relative pressure compared to nitrogen due to a weaker effective adsorption potential (lower strength of dispersion forces), including the absence of specific interactions of argon with the adsorbent surface. We show further that application of advanced theoretical approaches based on the density functional theory (NLDFT and QSDFT) provides an accurate description of the pore-size distribution (PSD). The PSD obtained from the argon adsorption data at 87.3 K is in good agreement with immersion calorimetry measurements. Our results demonstrate that argon adsorption at 87.3 K in combination with the application of advanced DFT methods (e.g. QSDFT) allows for a reliable characterization of the narrow microporosity in highly heterogeneous activated carbons. © 2011 Elsevier Ltd. All rights reserved.

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