CO2-pressure swing activation for efficient production of highly porous carbons

In this work, we describe a new type of activation method of carbon materials using pressure swing of CO2. The porosity development markedly depends on the pressure swinging frequency. The porous carbon obtained from pressure-swing activation shows an additional porosity development without pitting corrosion on the surface, which occurs on CO2 activation without pressure-swing. This phenomenon is ascribed to the enhancement of Knudsen diffusion and/or configurational diffusion of CO2 which is caused by an exterior stimulus from the pressure swing. (C) 2015 Elsevier Ltd. All rights reserved.ArticleCARBON. 85:245-248 (2015)journal articl

Comparative pore structure analysis of highly porous graphene monoliths treated at different temperatures with adsorption of N-2 at 77.4 K and of Ar at 87.3 K and 77.4 K

We prepared nanoporous graphene monolith of different porosity by high temperature treatment up to 2073 K in Ar. The porosity is comparatively evaluated with N-2 adsorption isotherms at 77.4 K and Ar adsorption isotherms at 87.3 K and 77.4 K. N-2 adsorption at 77.4 K shows an excess adsorption amount below 3 x 10(-3) of the relative pressure which is caused by the quadrupole moment of an N-2 molecule. This effect doesn't give significant influence on the determination of the total surface area from subtracting pore effect (SPE) method, the micropore volume from Dubinin-Radushkevich (DR) method and the total pore volumes from the Gurvitch rule. However, the peak of the micropore size distribution determined by Horvath-Kawazoe (HK) method from N-2 adsorption at 77.4 K shifts to a smaller size than that from Ar adsorption at 87.3 K by 0.05-0.09 nm. (C) 2015 Elsevier Inc. All rights reserved.ArticleMICROPOROUS AND MESOPOROUS MATERIALS. 209:72-78 (2015)journal articl

Air separation with graphene mediated by nanowindow-rim concerted motion

International audienceNanoscale windows in graphene (nanowindows) have the ability to switch between open and closed states, allowing them to become selective, fast, and energy-efficient membranes for molecular separations. These special pores, or nanowindows, are not electrically neutral due to passivation of the carbon edges under ambient conditions, becoming flexible atomic frameworks with functional groups along their rims. Through computer simulations of oxygen , nitrogen, and argon permeation, here we reveal the remarkable nanowindow behavior at the atomic scale: flexible nanowindows have a thousand times higher permeability than conventional membranes and at least twice their selectivity for oxygen/nitrogen separation. Also, weakly interacting functional groups open or close the nanowindow with their thermal vibrations to selectively control permeation. This selective fast permeation of oxygen, nitrogen, and argon in very restricted nanowindows suggests alternatives for future air separation membranes

Noticeable Reverse Shift in the Melting Temperatures of Benzene and Carbon Tetrachloride Confined within the Micropores and Mesopores of Hydrophobic Carbons

Carbon aerogels contain both mesopores and micropores. In this study, benzene/CCl4 was adsorbed in the pores of carbon aerogels (both mesopores and micropores) and their phase behaviours were examined using differential scanning calorimetry. The bulk solid benzene melted at 278 K and the melting temperatures of benzene confined inside the mesopores and micropores of carbon aerogels were 258 and 293 K, respectively. Although the melting temperature depression of condensates in mesopores is well known, the observed elevation of the melting temperature for micropores is very limited in the strongly interacted system. Similar melting behaviours were observed for the confined CCl4; depression by 45 K in mesopores and elevation by 48 K in micropores showed about two times the change as compared with that of confined benzene.ArticleADSORPTION SCIENCE & TECHNOLOGY. 31(2-3):145-151 (2013)journal articl

Selective probe of the morphology and local vibrations at carbon nanoasperities

We introduce a way to selectively probe local vibration modes at nanostructured asperities such as tips of carbon nanohorns. Our observations benefit from signal amplification in surface-enhanced Raman scattering (SERS) at sites near a silver surface. We observe nanohorn tip vibration modes in the range 200-500 cm(-1), which are obscured in regular Raman spectra. Ab initio density functional calculations assign modes in this frequency range to local vibrations at the nanohorn cap resembling the radial breathing mode of fullerenes. Careful interpretation of our SERS spectra indicates presence of caps with 5 or 6 pentagons, which are chemically the most active sites. Changes in the peak intensities and frequencies with time indicate that exposure to laser irradiation may cause structural rearrangements at the cap.ArticleJOURNAL OF CHEMICAL PHYSICS. 136(6):064505 (2012)journal articl

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1 cm3/g) and high packing density (0.7 g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160 cm3 (STP)/cm3 at 25 °C and 3.5 MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700 °C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175 cm3 (STP)/cm3 at 25 °C and 5 MPa and 200 cm3 (STP)/cm3 at 25 °C and 10 MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5 nm at pressure up to 10 MPa was estimated to understand their contribution to the total adsorption capacity.Authors acknowledge financial support from MINECO: Project MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) and Generalitat Valenciana (PROMETEO/2009/002)

High-Pressure Methane Storage in Porous Materials: Are Carbon Materials in the Pole Position?

Natural gas storage on porous materials (ANG) is a promising alternative to conventional on-board compressed (CNG) or liquefied natural gas (LNG). To date, Metal–organic framework (MOF) materials have apparently been the only system published in the literature that is able to reach the new Department of Energy (DOE) value of 263 cm3 (STP: 273.15 K, 1 atm)/cm3; however, this value was obtained by using the ideal single-crystal density to calculate the volumetric capacity. Here, we prove experimentally, and for the first time, that properly designed activated carbon materials can really achieve the new DOE value while avoiding the additional drawback usually associated with MOF materials (i.e., the low mechanical stability under pressure (conforming), which is required for any practical application).Authors acknowledge financial support from MINECO: Strategic Japanese−Spanish Cooperation Program (No. PLE2009-0052), Concert Project-NASEMS (No. PCIN-2013-057) and Generalitat Valenciana (No. PROMETEO/2009/002)