Joaquín Silvestre-Albero

High‐Surface‐Area Carbon Molecular Sieves for Selective CO2 Adsorption

A series of carbon molecular sieves (CMSs) has been prepared, either as powders or monoliths, from petroleum pitch using potassium hydroxide as the activating agent. The CMS monoliths are prepared without the use of a binder based on the self-sintering ability of the mesophase pitch. Characterization results show that these CMSs combine a large apparent surface area (up to ca. 3100 m(2) g(-1)) together with a well-developed narrow microporosity (V(n) up to ca. 1.4 cm(3) g(-1)). The materials exhibit high adsorption capacities for CO(2) at 1 bar and 273 K (up to ca. 380 mg CO(2) g sorbent(-1)). To our knowledge, this is the best result obtained for CO(2) adsorption using carbon-based materials. Furthermore, although the CO(2) adsorption capacity for activated carbons has usually been considered lower than that of zeolites, the reported values exceed the total amount adsorbed on traditional 13X and 5A zeolites (ca. 230 mg and 180 mg CO(2) g sorbent(-1), respectively), under identical experimental conditions. Additionally, the narrow pore openings found in the CMS samples (ca. 0.4 nm) allows for the selective adsorption of CO(2) from molecules of similar dimensions (e.g., CH(4) and N(2)).

Characterization of microporous solids by immersion calorimetry

Abstract This paper reviews the fundamentals and main applications of immersion calorimetry in the study of microporous adsorbents such as activated carbons, including carbon molecular sieves, and microporous zeolites. In the former case, it will be shown that immersion calorimetry into liquids of different molecular sizes easily allows for the assessment of the micropore size distribution. Furthermore, the use of liquids with different polarity permits the study of the evolution of the surface chemistry of these materials after different treatments. On the other hand, the study of zeolites with this technique is not as straightforward as in the case of carbonaceous materials, given the higher complexity of these systems. It will be shown that this technique can be used to analyze the evolution of the surface properties of zeolites A and X after thermal treatments at different temperatures and after ion-exchange.

Cluster-mediated filling of water vapor in intratube and interstitial nanospaces of single-wall carbon nanohorns

This study reports experimental data of water adsorption at 303 K on single-wall carbon nanohorns (SWNHs). The analysis of the water adsorption isotherms supports a cluster-mediated model for filling the interstitial and intratube nanospaces in contrast to the monolayer formation observed for simple nonpolar molecules. The enthalpies of water immersion of SWNHs with closed and open nanohorns show a very week interaction between the water molecules and the hydrophobic carbon nanotubular structure; the observed specific enthalpy of immersion expressed per unit surface area is lower than the reported values for graphite.

Ammonia removal using activated carbons: effect of the surface chemistry in dry and moist conditions.

The effect of surface chemistry (nature and amount of oxygen groups) in the removal of ammonia was studied using a modified resin-based activated carbon. NH(3) breakthrough column experiments show that the modification of the original activated carbon with nitric acid, that is, the incorporation of oxygen surface groups, highly improves the adsorption behavior at room temperature. Apparently, there is a linear relationship between the total adsorption capacity and the amount of the more acidic and less stable oxygen surface groups. Similar experiments using moist air clearly show that the effect of humidity highly depends on the surface chemistry of the carbon used. Moisture highly improves the adsorption behavior for samples with a low concentration of oxygen functionalities, probably due to the preferential adsorption of ammonia via dissolution into water. On the contrary, moisture exhibits a small effect on samples with a rich surface chemistry due to the preferential adsorption pathway via Brønsted and Lewis acid centers from the carbon surface. FTIR analyses of the exhausted oxidized samples confirm both the formation of NH(4)(+) species interacting with the Brønsted acid sites, together with the presence of NH(3) species coordinated, through the lone pair electron, to Lewis acid sites on the graphene layers.

Is there any microporosity in ordered mesoporous silicas

The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

Methane hydrate formation in confined nanospace can surpass nature

Natural methane hydrates are believed to be the largest source of hydrocarbons on Earth. These structures are formed in specific locations such as deep-sea sediments and the permafrost based on demanding conditions of high pressure and low temperature. Here we report that, by taking advantage of the confinement effects on nanopore space, synthetic methane hydrates grow under mild conditions (3.5 MPa and 2 °C), with faster kinetics (within minutes) than nature, fully reversibly and with a nominal stoichiometry that mimics nature. The formation of the hydrate structures in nanospace and their similarity to natural hydrates is confirmed using inelastic neutron scattering experiments and synchrotron X-ray powder diffraction. These findings may be a step towards the application of a smart synthesis of methane hydrates in energy-demanding applications (for example, transportation).

Catalytic nanomedicine: A new field in antitumor treatment using supported platinum nanoparticles. In vitro DNA degradation and in vivo tests with C6 animal model on Wistar rats

Novel nanostructured TiO2 and SiO2 based biocatalysts, with 3-4 wt. % of Pt have been developed. The obtained materials exhibit a high surface area together with a broad pore size distribution. The method of synthesis allowed obtaining high dispersed platinum metal nanoparticles. In vitro DNA reactivity test of the biocatalysts were carried out by electrophoresis and formation of DNA adducts was observed. The most active biocatalyst was H2PtCl6/SiO2. These biocatalysts were also tested in an experimental model of C6 brain tumours in Wistar rats. Administration of the material was made by stereotactic brain surgery to place it directly in the malignant tissue. A significant decrease in tumour size and weight as well as morphologic changes in cancer cells were observed.

Vapour phase hydrogenation of crotonaldehyde over magnesia-supported platinum–tin catalysts

Magnesia-supported bimetallic Pt–Sn catalysts with various metal contents and Pt/Sn atomic ratios were prepared using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2] or the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts were characterised by X-ray diffraction, transmission electron microscopy techniques and X-ray photoelectron spectroscopy. The bulk and surface composition of the catalysts was related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). It is shown that the various preparation methods produce catalysts with distinct properties and catalytic behaviour. For catalysts prepared with the bimetallic complex, the highest selectivity for the unsaturated alcohol (but-2-en-1-ol) was achieved for the catalyst containing larger bimetallic particles, which are associated with a higher surface concentration of oxidised tin species. The catalyst prepared with separate metal precursors contains a higher amount of residual chlorides, which significantly affect the catalytic activity but only slightly alter the selectivity for the hydrogenation of the carbonyl bond.

Carbon-supported ionic liquids as innovative adsorbents for CO2 separation from synthetic flue-gas

Fixed-bed thermodynamic CO2 adsorption tests were performed in model flue-gas onto Filtrasorb 400 and Nuchar RGC30 activated carbons (AC) functionalized with [Hmim][BF4] and [Emim][Gly] ionic liquids (IL). A comparative analysis of the CO2 capture results and N2 porosity characterization data evidenced that the use of [Hmim][BF4], a physical solvent for carbon dioxide, ended up into a worsening of the parent AC capture performance, due to a dominating pore blocking effect at all the operating temperatures. Conversely, the less sterically-hindered and amino acid-based [Emim][Gly] IL was effective in increasing the AC capture capacity at 353 K under milder impregnation conditions, the beneficial effect being attributed to both its chemical affinity towards CO2 and low pore volume reduction. The findings derived in this work outline interesting perspectives for the application of amino acid-based IL supported onto activated carbons for CO2 separation under post-combustion conditions, and future research efforts should be focused on the search for AC characterized by optimal pore size distribution and surface properties for IL functionalization.

Textural characterization of micro- and mesoporous carbons using combined gas adsorption and n-nonane preadsorption.

Porous carbon and carbide materials with different structures were characterized using adsorption of nitrogen at 77.4 K before and after preadsorption of n-nonane. The selective blocking of the microporosity with n-nonane shows that ordered mesoporous silicon carbide material (OM-SiC) is almost exclusively mesoporous whereas the ordered mesoporous carbon CMK-3 contains a significant amount of micropores (~25%). The insertion of micropores into OM-SiC using selective extraction of silicon by hot chlorine gas leads to the formation of ordered mesoporous carbide-derived carbon (OM-CDC) with a hierarchical pore structure and significantly higher micropore volume as compared to CMK-3, whereas a CDC material from a nonporous precursor is exclusively microporous. Volumes of narrow micropores, calculated by adsorption of carbon dioxide at 273 K, are in linear correlation with the volumes blocked by n-nonane. Argon adsorption measurements at 87.3 K allow for precise and reliable calculation of the pore size distribution of the materials using density functional theory (DFT) methods.