Methane sorption on ordered mesoporous carbon in the presence of water

An ordered mesoporous carbon was synthesized using SBA-15 as the template. The sorption isotherms of methane on the synthesized carbon material were collected. Its ordered structure was confirmed by the XRD, SEM and TEM examinations. The BET surface area is 1100-1200 m²/g, the total pore volume is 1.24-1.30 cm³/g, and the pore size distribution is very narrow and centered at 2-5 nm. As high as 41.2 wt.% of methane was stored per unit mass of carbon at 275 K and pressures less than 7 MPa in the presence of 3.86 times more water. This sorption amount is 31% higher than the largest sorption capacity reached by activated carbon in the presence of water, which was equal to or higher than the storage capacity of compression till 20 MPa. The enthalpy change corresponding to the sudden change of isotherms was equal to the enthalpy change of methane hydrate formation; therefore, the mechanism of the enhanced methane storage was considered due to the formation of methane hydrate in the porous carbon material.     

Carbon foams prepared from polyimide using urethane foam template

Polyimide and carbon foams were successfully prepared using polyurethane foams as a template. Impregnation of polyimide precursor, poly(amide acid), followed by imidization at 200 °C gave polyurethane/polyimide (PU/PI) composite foams, which resulted in PI foams by heating above 400 °C and then carbon foams above 800 °C. Foams carbonized at 1000 °C were graphitized by the heat treatment at 3000 °C, keeping foam characteristics. Two applications of these carbon foams, i.e., an adsorbent of ambient water vapor and a substrate of photocatalyst anatase TiO₂, were experimentally confirmed. For the former application, the present foam could be characterized by prompt adsorption of ambient water vapor. Some of carbon foams prepared were floating on water, even after loading photocatalyst anatase, which might be advantageous for photodecomposition of pollutants in water in respect to the UV rays efficiency.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

Xe NMR studies on carbon replicas of Y zeolite

¹²⁹Xe NMR spectroscopy of xenon gas adsorbed on carbon replicas of Y zeolite was carried out at room temperature. Corresponding carbon replicas have been prepared by using ethylene and HY zeolite in a pressure reactor. Xenon gas was adsorbed on the resulting carbon samples in the pressure range from 40 to 150 kPa. The plot of the chemical shift against xenon pressure was found to be a linear function in the investigated pressure range from 40 to 150 kPa. Intense and narrow peaks have been observed for the synthesized carbon samples indicating chemically pure samples. By comparison of the estimated chemical shift parameter δ_N→0 and the slope δ₁ of the shift versus density plots the existence of different pore sizes could be revealed. These observed differences can be attributed to different types of micropores generated by shrinkage effects during carbon liberation from the parent zeolite host. The obtained carbon replicas of Y zeolite were further characterized by elemental analysis, XPS, ¹³C MAS NMR and ESR spectroscopy.     

Templating synthesis of ordered mesoporous carbon particles

This research reports the synthesis of spherical ordered mesoporous carbon particles using mesoporous silica particles as a template. The silica particles with ordered cubic and lamellar mesostructures were synthesized from an aerosol-assisted self-assembly process using block copolymer surfactants as the structural directing agent. Infiltrating the pores of the silica particles with a sucrose solution followed by carbonization, and silica removal results in mesoporous carbon particles with replicated mesostructures. The particles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nitrogen sorption techniques.     

Templated synthesis of mesoporous carbon from sucrose—the way from the silica pore filling to the carbon material

Mesoporous carbon materials were synthesized using sucrose as carbon precursor and commercial silica as template. Every step of the synthesis such as pore filling, loss of carbon precursor during carbonization and development of the carbon pore system during silica removal have been investigated in detail. As a criterion for the quality of the obtained carbon materials, the pore size distribution estimated by applying density functional theory was used.     

Improvement of mesoporosity of carbon cryogels by acid treatment of hydrogels

Wattle tannin–furfural (TFu) gels are synthesized by the sol–gel polycondensation of wattle tannin with furfural by using sodium hydroxide as a catalyst and cured at 363 K. After cured, the TFu hydrogels are treated in hydrochloric acid (HCl) solutions with various variables as follows: aging temperature, HCl concentration and pH. TFu cryogels aged are then freeze-dried and pyrolyzed under an inert atmosphere to obtain TFu carbon cryogels. The TFu and carbon cryogels were characterized by N₂ adsorption and scanning electron microscope. The high HCl concentration yields the increase of mesopore volume almost twice especially at high temperature and the mesopore size distribution can be greatly developed sharper and narrower when the high concentration of HCl or/and the high temperature are used. Moreover, this method is the versatile approach for developing the mesopore structure of the low and high porous TFu hydrogels and has no serious problem of weight loss after treatment.     

Control of mesoporous properties of carbon cryogels prepared from wattle tannin and furfural

Wattle tannin–furfural (TFu) carbon cryogels are synthesized by sol–gel polycondensation of wattle tannin with furfural by using sodium hydroxide (NaOH) as a catalyst, dried by freeze-drying technique and then pyrolyzed under inert atmosphere, respectively. The amounts of wattle tannin (T), furfural (Fu), NaOH (C) and distilled water (W) are changed for preparing the mesoporous TFu carbon cryogels. The mole ratio of tannin to catalyst T/C plays a crucial role for the synthesis of TFu organic and carbon cryogels. The results suggest that the T/C ratio should be above 0.25 but <1.0 to prepare the mesoporous and homogeneous cryogels. Although TFu carbon cryogels have the broad mesopore size distribution, the mesoporous structure is controllable by the synthesis conditions. The carbon cryogels possess the mesopore volume less than 0.56 cm³/g and the BET surface area less than 600 m²/g. Moreover, the ratio of catalyst to water C/W can be used to prepare the homogeneous and mesoporous carbon cryogels, and to control the mesopore radius of carbon cryogels in the range of 1.6–9.6 nm.     

3D interconnected macroporous carbon monoliths prepared by ultrasonic irradiation

A new method in preparation of 3D interconnected macroporous carbon monolith has been introduced. Ultrasonic irradiation (ultrasonic intensity 78 W/cm²) and low catalyst concentration (C/W = 10 mol/m³) of RF solution are used as an interesting and unique preparation method for 3D interconnected macroporous sonogel (gel irradiated by ultrasound at gelation stage) and/or 3D interconnected macroporous carbon monolith without using templates.     

Synthesis and characterization of microporous carbons templated by ammonium-form zeolite Y

Emerging applications such as gas storage require porous carbon materials with tailored structural and surface properties. Template synthesis approach to porous carbons offers opportunities for tailoring these properties. In this study, ammonium-form zeolite Y (NH₄Y) was used as a template and furfuryl alcohol (FA) was employed as a carbon precursor to prepare microporous carbons by simple impregnation method. The effects of synthesis conditions such as carbonization temperatures and heating rates on the pore structure of the microporous carbons were investigated. The thermal behaviors of FA-NH₄Y mixtures and zeolite/carbon composites were studied by thermogravimetric analysis (TGA). The physical, structural, and surface properties of the microporous carbons were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), elemental analysis, and physical adsorption of nitrogen. Microporous carbons with high surface areas, pore volumes and nitrogen-containing surface functional groups can be readily synthesized.     

Adsorption of l-histidine over mesoporous carbon molecular sieves

Mesoporous carbon, CMK-3, was prepared by large pore hexagonal mesoporous silica SBA-15. The structural order and textural properties of all the materials were studied by XRD, HRTEM, and nitrogen adsorption. Adsorption of l-histidine (His) over various porous adsorbents such as CMK-3, SBA-15, and activated carbon was studied from solutions with different pH. His adsorption was observed to be pH dependent with maximum adsorption near the isoelectric point of the amino acid. CMK-3 showed a larger amount of His adsorption as compared to SBA-15 and the conventional adsorbent, namely activated carbon. CMK-3 registers the total adsorption capacity of ca. 1350 μmol g⁻¹ which is ca. 12 times higher than the adsorption capacity of SBA-15. This large difference could be mainly due to the stronger hydrophobic interaction between the non-polar side chains of amino acids and the hydrophobic surface of the mesoporous carbon as compared to mesoporous silica. The influence of ionic strengths on the adsorption of His was also studied and the results are discussed. Nitrogen adsorption of CMK-3 after His adsorption confirmed that His molecules are tightly packed inside the mesopores.     

Preparation of colloidal microporous carbon spheres from furfuryl alcohol

Colloidal microporous carbon (MC) spheres with an average size of 260 nm-1.5 μm were prepared by carbonization of “nonstick” poly(furfuryl alcohol) (PFA) spheres, which were synthesized by a two-step polymerization of furfuryl alcohol (FA) involving slow polymerization (1st step) and sphere formation (2nd step). The high dispersibility of the MC spheres was simultaneously realized by removing surface functional groups of the PFA spheres with the evaporation-induced concentrated sulfuric acid (2nd step). By varying the temperature of slow polymerization, the spheres with different sizes could be simply synthesized. The studies also showed that surfactant and sulfuric acid treatment played an important role in the synthesis of colloidal PFA (MC) spheres.     

Imaging the structure and porosity of active carbons by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been employed for a comparative structural characterization, down to the atomic scale, of a representative set of porous carbons with different adsorption characteristics and prepared either by activation (physical or chemical) or templating techniques. The studied materials included a chemically activated, supermicroporous high surface area carbon, two activated carbons containing both micro- and mesopores synthesized by physical activation, an ultramicroporous carbon molecular sieve, and an ordered microporous carbon templated in the nanochannels of zeolite Y. In general, good agreement was found between the porous structures as imaged by STM and the porous texture derived from gas adsorption data for all the carbons investigated. The activated carbon samples were dominated by networks of slit type micropores and, in some cases, by mesopores of varied morphologies. By contrast, the zeolite-templated carbon exhibited rounded micropore morphology, and the carbon molecular sieve displayed a rather featureless conformation dominated by voids only below 1 nm wide. The structural differences observed by STM were interpreted in terms of the different preparation procedures of the studied carbons. In particular, the templated carbon consisted of minute clusters about 1 nm in diameter that were interpreted to be formed within the extremely confined, microporous spaces of the zeolite Y template.     

Easy synthesis of an ordered mesoporous carbon with a hexagonally packed tubular structure

Ordered mesoporous carbon with hexagonal arrays of tubes (CMK-5) was successfully synthesized via a nanocasting process by directly using SBA-15, instead of AlSBA-15, as a template, furfuryl alcohol as a carbon source and oxalic acid as the catalyst. The time consuming impregnation of SBA-15 with aluminum could be saved. The as-synthesized CMK-5 exhibits a tubular structure with double pore system. The loading amount of carbon precursor on the pore walls of SBA-15 is the key factor for the formation of the CMK-5 structure with two-dimensional hexagonal arrays of tubes, and the pore diameter can be adjusted by varying the loading amount of the carbon precursor. The CMK-5 carbon exhibits high apparent surface area up to ∼2500 m²/g and high pore volume reaching ∼2 cm³/g, which is due to the unique structure of CMK-5. The characterization results confirmed that carbonization under argon atmosphere instead of vacuum is sufficient for the structural formation of CMK-5 carbons, and can be used as an alternative pathway to prepare tubular-type carbons.