|C. Falco, J.P. Marco-Lozar, D. Salinas-Torres, E. Morallón, D. Cazorla-Amorós, M.M. Titiricic, D. Lozano-Castelló|
Tailoring the porosity of chemically activated hydrothermal carbons: Influence of the precursor and hydrothermal carbonization temperature, Carbon, in press, June 2013.
Advanced porous materials with tailored porosity (extremely high development of microporosity together with a narrow micropore size distribution (MPSD)) are required in energy and environmental related applications. Lignocellulosic biomass derived HTC carbons are good precursors for the synthesis of activated carbons (ACs) via KOH chemical activation. However, more research is needed in order to tailor the microporosity for those specific applications. In the present work, the influence of the precursor and HTC temperature on the porous properties of the resulting ACs is analyzed, remarking that, regardless of the precursor, highly microporous ACs could be generated. The HTC temperature was found to be an extremely influential parameter affecting the porosity development and the MPSD of the ACs. Tuning of the MPSD of the ACs was achieved by modification of the HTC temperature. Promising preliminary results in gas storage (i.e., CO2 capture and high pressure CH4 storage) were obtained with these materials, showing the effectiveness of this synthesis strategy in converting a low value lignocellulosic biomass into a functional carbon material with high performance in gas storage applications.
|Ana Silvestre-Albero, Soledad Rico-Francés, Francisco Rodríguez-
Reinoso, Andreas M. Kernb, Michael Klumpp, Bastian J.M. Etzold, Joaquín Silvestre-Albero
High selectivity of TiC-CDC for CO2/N2separation, Carbon, August 2013 Vol. 59, 221–228.
A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500–1200 °C). Contrary to N2 adsorption measurements at −196 °C, CO2 adsorption measurements at room temperature and high pressure (up to 1 MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000 °C). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO2 adsorption under standard conditions (0 °C and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N2 at a lower adsorption temperature (−196 °C), i.e. textural parameters obtained from N2 adsorption measurements on CDC must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH4 with a slightly larger diameter (0.39 nm) is able to partially access the inner porous structure whereas N2, with a slightly smaller diameter (0.36 nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO2 capture in flue-gas streams.
|Juan Pablo Marco-Lozar, Mirko Kunowsky, Fabia´n |
Sua´ rez-Garcia, Angel Linares-Solano
Sorbent Design for CO2 Capture Under Different Flue Gas Conditions, Carbon, 2014, in press.
CO2 capture by solid sorbents is a physisorption process in which the gas molecules are adsorbed in a different porosity range, depending on the temperature and pressure of the capture conditions. Accordingly, CO2 capture capacities can be enhanced if the sorbent has a proper porosity development and a suitable pore size distribution. Thus, the main objective of this work is to maximize the CO2 capture capacity at ambient temperature, elucidating which is the most suitable porosity that the adsorbent has to have as a function of the emission source conditions. In order to do so, different activated carbons have been selected and their CO2 capture capacities have been measured. The obtained results show that for low CO2 pressures (e.g., conditions similar to post-combustion processes) the sorbent should have the maximum possible volume of micropores smaller than 0.7 nm. However, the sorbent requires the maximum possible total micropore volume when the capture is performed at high pressures (e.g., conditions similar to oxy-combustion or pre-combustion processes). Finally, this study also analyzes the important influence that the sorbent density has on the CO2 capture capacity, since the adsorbent will be confined in a bed with a restricted volume.
|Marco-Lozar, J.P., Kunowsky, M., Carruthers, J.D., Linares-Solano,
Gas Storage Scale-up at Room Temperature on High Density Carbon Materials, Carbon (2014),
In relation to the current interest on gas storage demand for environmental applications (e.g., gas transportation, and carbon dioxide capture) and for energy purposes (e.g., methane and hydrogen), high-pressure adsorption (physisorption) on highly porous sorbents has become an attractive option. Considering that for high-pressure adsorption, the sorbent requires both, high porosity and high density, the present paper investigates gas storage enhancement on selected carbon adsorbents, both on a gravimetric and on a volumetric basis. Results on carbon dioxide, methane, and hydrogen adsorption at room temperature (i.e., supercritical and subcritical gases) are reported. From the obtained results, the importance of both parameters (porosity and density) of the adsorbents is confirmed. Hence, the densest of the different carbon materials used is selected to study a scale-up gas storage system, with a 2.5 l cylinder tank containing 2.64 kg of adsorbent. The scale-up results are in agreement with the laboratory scale ones and highlight the importance of the adsorbent density for volumetric storage performances, reaching, at 20 bar and at RT, 376 g l-1, 104 g l-1, and 2.4 g l-1 for CO2, CH4,and H2, respectively.
Kripal S. Lakhi, Wang Soo Cha, Stalin Joseph, Barry J. Wood, Salem S. Aldeyab, Geoffrey Lawrence, Jin-Ho Choy, Ajayan Vinu|
Cage Type Mesoporous Carbon Nitride with Large Mesopores for CO2 Capture, Catalysis Today, 243, 1 April 2015, 209–217.
Mesoporous carbon nitrides with well-ordered 3D porous structure and large, tuneable cage-type mesopores (MCN-7) have been prepared through a straightforward polymerization of ethylenediamine (EDA) and carbon tetrachloride (CTC) inside the pore channels of FDU-12 with different pore diameters. The obtained MCN-7 were characterized using small angle X-ray diffraction, N2 adsorption, high resolution transmission electron microscopy(HRTEM), high resolution scanning electron microscopy (FE SEM), Fourier transform infra-red, electron energy loss and X-ray photoelectron spectroscopy, and CHN analysis. The characterization results reveal that the structure of the MCN-7 is highly ordered and the pore structure of the templates are perfectly replicated into the carbon nitrides (CN). Nitrogen adsorption results indicate that the pore diameter of MCN-7 is directly controlled by the pore diameter of the template and can be tuned with a simple adjustment of the pore size of the template. The XPS and FT-IR data confirm that the wall structure of the samples are composed of CN framework with terminal amine groups that are exposed on the surface and are important for the capture of CO2 molecules. MCN-7 with different pore diameters and specific surface area are used as adsorbents for the capture of CO2 molecules at different high pressures (0–30 bar) and temperatures (0–25 °C). The MCN-7 materials show excellent affinity towards CO2 molecules because of the strong acid base interactions. It is found that the amount of the CO2 adsorbed over the MCN-7 is mainly dependent on the BET surface area, and the structural order, and pore diameter of the adsorbent. MCN-7 with the highest specific surface area shows higher CO2 adsorption capacity than that of other materials including MCN with one dimensional structure.
| Mirian E. Casco, Manuel Martínez-Escandell, Joaquín Silvestre-AlberoCorresponding, Francisco Rodríguez-Reinoso
Effect of the porous structure in carbon materials for CO2capture at atmospheric and high-pressure, Carbon (2014),
Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO2 capture both at atmospheric (∼168mg CO2/g at 298 K) and high pressure (1500mg CO2/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure,in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores(pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high-pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO2/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.
|Cristina Ruiz-García, Javier Pérez-Carvajal, Angel Berenguer-Murcia, Margarita Darder, Pilar Aranda, Diego Cazorla-Amorós, Eduardo Ruiz-Hitzky|
Clay-supported graphenes: application to hydrogen storage, Phys. Chem. Chem. Phys., 2013, 15, 18635-18641
The present work refers to clay–graphene nanomaterials prepared by a green way using caramel from sucrose and two types of natural clays (montmorillonite and sepiolite) as precursors, with the aim of evaluating their potential use in hydrogen storage. The impregnation of the clay substrates by caramel in aqueous media, followed by a thermal treatment in the absence of oxygen of these clay–caramel intermediates gives rise to graphene-like materials, which remain strongly bound to the silicate support. The nature of the resulting materials was characterized by different techniques such as XRD, Raman spectroscopy and TEM, as well as by adsorption isotherms of N2, CO2, and H2O. These carbon–clay nanocomposites can act as adsorbents for hydrogen storage, achieving, at 298 K and 20 MPa, over 0.1 wt% of hydrogen adsorption excess related to the total mass of the system, and a maximum value close to 0.4 wt% of hydrogen specifically related to the carbon mass. The very high isosteric heat for hydrogen sorption determined from adsorption isotherms at different temperatures (14.5 kJ mol−1) fits well with the theoretical values available for hydrogen storage on materials that show a strong stabilization of the H2 molecule upon adsorption.
|Javier Sanchez-Lainez, Beatriz Zornoza, Alvaro Mayoral, Angel Berenguer- Murcia, Diego Cazorla-Amoros, Carlos Tellez, Joaquin Coronas
Beyond the H2/CO2 upper bound: one-step crystallization and separation of nano-sized ZIF-11 by centrifugation and its application in mixed matrix membranes, J. Mater. Chem. A, 2015, Advance Article
The synthesis of nano-sized ZIF-11 with an average size of 36 ± 6nm is reported. This material has been named nano-zeolitic imidazolate framework-11 (nZIF-11). It has the same chemical composition and thermal stability and analogous H2 and CO2 adsorption properties to the conventional microcrystalline ZIF-11 (i.e. 1.9 ± 0.9 μm). nZIF-11 has been obtained following the centrifugation route, typically used for solid separation, as a fast new technique (pioneering for MOFs) for obtaining nanomaterials where the temperature, time and rotation speed can easily be controlled. Compared to the traditional synthesis consisting of stirring + separation, the reaction time was lowered from several hours to a few minutes when using this centrifugation synthesis technique. Employing the same reaction time (2, 5 or 10 min), micro-sized ZIF-11 was obtained using the traditional synthesis while nano-scale ZIF-11 was achieved only by using centrifugation synthesis. The small particle size obtained for nZIF-11 allowed the use of the wet MOF sample as a colloidal suspension stable in chloroform. This helped to prepare mixed matrix membranes (MMMs) by direct addition of the membrane polymer (polyimide Matrimid®) to the colloidal suspension, avoiding particle agglomeration resulting from drying. The MMMs were tested for H2/CO2 separation, improving the pure polymer membrane performance, with permeation values of 95.9 Barrer of H2 and a H2/CO2 separation selectivity of 4.4 at 35 °C. When measured at 200 °C, these values increased to 535 Barrer and 9.1.
|Cristina Schitco, Mahdi Seifollahi Bazarjani, Ralf Riedel and Aleksander Gurlo|
Ultramicroporous silicon nitride ceramics for CO2 capture, Journal of Materials Research, 2015.
Carbon dioxide (CO2) capture is regarded as one of the biggest challenges of the 21st century; therefore, intense research effort has been dedicated in the area of developing new materials for efficient CO2 capture. Here, we report high CO2 capture capacity in the low region of applied CO2 pressures observed with ultramicroporous silicon nitride-based material. The latter is synthesized by a facile one-step NH3-assisted thermolysis of a polysilazane. Our newly developed material for CO2 capture has the following outstanding properties: (i) one of the highest CO2 capture capacities per surface area of micropores, with a CO2 uptake of 2.35 mmol g−1 at 273 K and 1 bar (ii) a low isosteric heat of adsorption (27.6 kJ mol−1), which is independent from the fractional surface coverage of CO2. Furthermore, we demonstrate that the pore size plays a crucial role in elevating the CO2 adsorption capacity, surpassing the effect of Brunauer–Emmett–Teller specific surface area.
|Kripal S. Lakhi, Arun V. Baskar, Javaid S. M. Zaidi, Salem S. Al-Deyab,
Mohamed El-Newehy, Jin-Ho Choyc and Ajayan Vinu
Morphological control of mesoporous CN based hybrid materials and their excellent CO2 adsorption capacity, RSC Advances, Issue 50, 2015.
Highly ordered mesoporous carbon nitrides (MCN-1-Ts) with uniform rod shaped morphology have been synthesized by a hard templating technique using SBA-15 silicas prepared a under hydrothermal “static” condition at different temperatures as templates following a simple polymerization reaction between carbon tetrachloride (CTC) and ethylenediamine (EDA) inside the large pores of SBA-15. The static hydrothermal condition offers uniform rod shaped morphology for the template materials which has been completely replicated into the MCN nanostructures. The obtained materials were characterized with low angle XRD, N2 adsorption, high resolution transmission electron microscopy, high resolution scanning electron microscopy (FE SEM), Fourier transform infra-red (FT-IR), and X-ray photoelectron spectroscopy (XPS). The characterization results confirm the successful replication of the ordered structure, morphology and mesoporosity of the template material into carbon nitride. The FT-IR and XPS techniques confirm the presence of free –NH and –NH2 groups on the surface of MCN, which are critical for capturing CO2. Finally, these materials with high surface area and uniform morphology are used as adsorbents for high pressure CO2 adsorption at different temperatures of 0, 10 and 25°C. It is found that the morphology of the materials which has a direct relation with the textural parameters plays a significant role in enhancing the amount of CO2 adsorption. The MCN with the uniform morphology and the highest surface area registers the highest CO2 adsorption capacity (16.5 mmol g−1) at 0°C and 30 bar pressure, which is found to be higher than that of the previously reported 3D- cage type MCN, activated carbon, multiwalled carbon nanotubes and mesoporous silicas.