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1.
Porous carbon beads were prepared from macroporous anion-exchange resin beads preliminary converted into resin-zeolite Beta composite or pure zeolite Beta spheres. Two synthesis procedures were used depending on the initial template employed. In a series of experiments, the resin from the resin-zeolite Beta composite was directly carbonized into carbon. In another series of experiments, the resin was removed by oxidation at 600 °C leaving behind self-bonded zeolite Beta beads, which were filled with carbon by chemical vapor deposition (CVD) of propylene. As a final step for both procedures, the zeolite was dissolved in hydrofluoric acid. All the carbons prepared inherited the macroscopic spherical shape of the template spheres as well as the morphology of the primary particles building up the beads. The synthesis procedure and the carbonization temperature or the temperature for CVD of carbon employed influenced the ordering and the pore structure of the produced carbons. The carbons prepared by direct carbonization showed relatively low surface areas, less than 1000 m2 g−1, and no zeolite structural regularity. The samples obtained via CVD maintained the zeolite ordering with a periodicity of 11.7 Å and had surface areas of over 2000 m2 g−1.  相似文献   

2.
Microporous activated carbons were prepared using zeolite NaY as the template and benzene as the carbon precursor. Chemical vapor deposition of benzene was conducted in the temperature range of 600–950 °C and under different flow rates of benzene. The structural properties of the derived carbons were characterized with various experimental techniques. It was found that the CVD temperature of 650 °C results in carbons with the highest surface area of 1,511 m2/g, a pore volume of 0.93 cm3/g, and a good structural regularity. The higher CVD temperatures (e.g. ~900 °C) were found to result in carbons with lower surface area and poor structural regularity. The increased benzene flow rate will result in carbons with lower surface area and larger pore sizes.  相似文献   

3.
The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxide/nitrogen) at 700-950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850°C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.  相似文献   

4.
Yongde Xia  Yanqiu Zhu  Yi Tang 《Carbon》2012,50(15):5543-5553
Structurally well ordered, sulfur-doped microporous carbon materials have been successfully prepared by a nanocasting method using zeolite EMC-2 as a hard template. The carbon materials exhibited well-resolved diffraction peaks in powder XRD patterns and ordered micropore channels in TEM images. Adjusting the synthesis conditions, carbons possess a tunable sulfur content in the range of 1.3–6.6 wt.%, a surface area of 729–1627 m2 g?1 and a pore volume of 0.60–0.90 cm3 g?1. A significant proportion of the porosity in the carbons (up to 82% and 63% for surface area and pore volume, respectively) is contributed by micropores. The sulfur-doped microporous carbons exhibit isosteric heat of hydrogen adsorption up to 9.2 kJ mol?1 and a high hydrogen uptake density of 14.3 × 10?3 mmol m?2 at ?196 °C and 20 bar, one of the highest ever observed for nanoporous carbons. They also show a high CO2 adsorption energy up to 59 kJ mol?1 at lower coverages (with 22 kJ mol?1 at higher CO2 coverages), the highest ever reported for any porous carbon materials and one of the highest amongst all the porous materials. These findings suggest that S-doped microporous carbons are potential promising adsorbents for hydrogen and CO2.  相似文献   

5.
Kaisheng Xia  Jinhua Jiang  Juan Hu 《Carbon》2008,46(13):1718-1726
Various porous carbons were prepared by CO2 activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO2 treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO2 treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO2 activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO2 treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm3 at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m2/g), large pore volume (2.09 cm3/g), as well as well-balanced microporosity and mesoporosity.  相似文献   

6.
Huanlei Wang  Juan Hu  Zhi Chen 《Carbon》2009,47(9):2259-152
Nanoporous carbon materials were synthesized by a two-step casting process using zeolite 13X as template. The nanoporous structures were characterized by X-ray diffraction, high resolution transmission electron microcopy and nitrogen sorption at 77 K, and the results show that pore filling in the zeolite channels could play an important role in the replication of zeolite-like structural order. Better pore filling led to a more ordered structure as well as higher surface area and pore volume. Further potassium hydroxide (KOH) activation improved the microporous texture to the carbon framework and resulted in higher surface area and pore volume. A large hydrogen uptake capacity of 6.30 wt.% has been achieved at 77 K and 20 bar. Besides, a high gravimetric capacitance of up to 160 F g−1 and an energy density of 30 W h kg−1 have been obtained when tested as an electrode for supercapacitors. The high performance in cryogenic hydrogen storage and electrochemical capacitance were closely correlated with the pore structures of the carbon materials.  相似文献   

7.
As reported in previous communications, novel porous carbons were synthesized by using zeolite Y as a template. The carbons possess a periodic ordering structure and high BET surface area with large micropore volume. In this work, the details of the synthesis methods for preparing the ordered microporous carbons were examined. It was found that the following two-step process, the filling of carbon into zeolite channels by impregnation of furfuryl alcohol and then chemical vapor deposition (CVD) of propylene, was indispensable for preparing carbon with highly periodic ordering. In addition, low-temperature CVD and the further heat treatment of zeolite/carbon composite after the CVD are key points for the appearance of both good long-range periodicity and very high BET surface area with almost no mesoporosity in the carbons.  相似文献   

8.
Svetlana Bashkova 《Carbon》2007,45(6):1354-1363
The catalytic oxidation of hydrogen sulphide (H2S) on various activated carbon materials was studied. The effects of pore structure, surface characteristics, and nitrogen content on the activity and selectivity of the carbons towards oxidation of H2S were investigated. It was found that a high volume of both micropores and small mesopores, in combination with a relatively narrow pore size distribution, were crucial for the retention of sulphur dioxide (SO2), a by-product of H2S oxidation. For the retention of carbonyl sulphide (COS), another H2S oxidation by-product, high surface reactivity with a significant amount of basic groups were found to be important. The only carbon with all these characteristics, and consequently the carbon that was able to retain both H2S and COS for an extended period of time, was an experimental product, “WSC”. This carbon was found to be superior to the other carbons studied, exhibiting high activity and selectivity for oxidation of H2S to sulphur. H2S breakthrough capacities and selectivity values of the carbons were found to be dependent on the nitrogen content of the carbons. In a hydrogen stream, carbons possessing the highest nitrogen contents exhibited the greatest H2S breakthrough capacities but, at the same time, the lowest selectivity with respect to sulphur formation. In reformate streams, the maximum breakthrough capacity and greatest selectivity were exhibited by carbons with a nitrogen content of about 1-1.5 wt%.  相似文献   

9.
《Carbon》2002,40(9):1507-1519
Synthetic activated carbons were prepared by H3PO4 activation of a chloromethylated and sulfonated copolymer of styrene and divinylbenzene, using an impregnation weight ratio of 0.75 and carbonization temperatures in the 400-1000 °C range. Other impregnation ratios (0.93 and 1.11) were also used at a carbonization temperature of 800 °C. The porous texture of the resulting carbons was characterized by N2 adsorption at −196 °C and CO2 adsorption at 0 °C. All carbons exhibited a multimodal pore size distribution with maxima in the micropore and meso/macropore regions. Maxima in pore volume were attained at 900 °C for micropores and at 500 and 900 °C for mesopores. The mesopore volume was less sensitive than the micropore volume to changes in the impregnation ratio. It is concluded that the porous texture is not a prime factor in determining the outstanding cation exchange capacities of these carbons.  相似文献   

10.
Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 °C, rate of heating less than 3 °C/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a ‘Coconut’ carbon molecular sieve, but the latter has both a higher CO2 adsorption capacity and a higher coefficient of N2/O2 separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 °C/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 °C. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 °C/min. The activation of lignin-char with steam at 800 °C resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm3 g−1) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH4 mixture. The size of the micropores was varied as a function of burn off value.  相似文献   

11.
To prepare porous carbons with high adsorption capacity from rice straws, two different kinds of precursors, i.e. one as the raw rice straws (one-stage process) and the other as pre-carbonized rice straws (two-stage process), were activated with KOH of various impregnation ratios. The two-stage process was found very effective for manufacturing porous carbons with high surface area and adsorption capacities for MB and I2. For example, the porous carbon that was carbonized at 700°C and subsequently activated at 900°C exhibited the surface area of 2410 m2/g, the adsorption capacities of 800 and 1720 mg/g for MB and I2, respectively, and the total pore volume of 1.4 ml/g. In the two-stage method, there was a preferential optimum impregnation ratio of KOH to a precursor carbon, i.e. 4:1, with which high surface area of porous carbons could be achieved. The formation of uni- and bidentate carboxylic salt structure, induced by reaction between KOH and oxygen containing carbon, that facilitates the formation of azo group (-NN-) on a subsequent heat treatment was considered as one of the key factors for the presence of optimum impregnation ratio of KOH. In contrast, the porous carbons of only moderate adsorption capacity could be obtained from the one-stage method. The original morphology of rice straw was sustained during the two-stage process, yet not during the one-stage process.  相似文献   

12.
Microporous–mesoporous carbons were synthesized via colloidal silica templating using Kraft lignin as a carbon precursor, which is a waste byproduct from paper industry. A unique feature of these carbons are uniform spherical mesopores achieved after dissolving colloidal silica used as a hard template, while micropores were created by post-synthesis CO2 activation. The resulting activated lignin-based carbons possessed high specific surface area (up to 2000 m2/g) and microporosity and mesoporosity easily tunable by adjusting activation conditions and optimizing the amount and particle size of the colloidal silica used. The total pore volumes of activated carbons obtained by using 20 and 13 nm silica colloids as a hard template exceeded 1 and 2 cm3/g, respectively.  相似文献   

13.
The pyrolysis of polyfurfuryl alcohol was studied up to 600 °C. Micropores appear in the carbon as early as 300 °C along with a significant amount of mesopores. As the pyrolysis temperature is increased, microporosity is retained, but the mesoporosity disappears. At 600 °C the material is microporous with a monodisperse pore size distribution centered at 4-5 Å. Infrared, X-ray photoelectron, and nuclear magnetic resonance spectroscopies, in combination with thermogravimetric analysis provide evidence that between 300 and 400 °C, both polyaromatic domains decorated with hydrogen and oxygen (hetero) atoms and partially decomposed polymer chains coexist. The unreacted polymer and heteroatoms induce mesoporosity by buffering the micropores created by polyaromatic domains. Raising the pyrolysis above 400 °C releases the buffering material, thereby collapsing the mesopores.  相似文献   

14.
Hsin-Yu Liu 《Carbon》2005,43(3):559-566
Mesoporous carbon was prepared from resol-type phenol-formaldehyde resin using mesoporous silica as template. By filling the resin into the pores of the template, followed by resin carbonization and template dissolution, mesoporous carbon preparation can be significantly simplified. Small-angle X-ray diffraction reflected the long-range ordering of the pores in the carbon. TEM and N2-adsorption analysis showed that the carbon contained mesopores of different sizes and a high proportion of micropores. Electrochemical cyclic voltammetry was conducted in H2SO4 to examine the surface accessibility of the carbon for double layer formation. Microporous activated carbon, also from the resol resin, was prepared for comparison. Although the pore sizes are different, the double-layer capacitances per unit area for both carbons are similar at low potential sweep rates. However, the capacitance decline with the sweep rate was less significant for the mesoporous carbon. Upon gasification of the carbons to increase their surface area, the ultimate capacitance per unit carbon area was enhanced and the enhancement was slightly larger for the mesoporous carbon. It is suggested that the presence of mesopores has facilitated the electrolyte migration into carbon interior. A two-electrode capacitor assembled with the mesoporous carbon was shown to have a small resistance and still exhibited a capacitive behavior at high potential sweep rates.  相似文献   

15.
An efficient post-cure approach has been demonstrated for the kilogram-scale synthesis of high-quality ordered mesoporous carbons (OMC) by using triblock copolymer Pluronic F127 as a template, phenolic resol as a carbon precursor and polyurethane foam as a sacrificial scaffold through an organic–organic self-assembly. The effects of the concentration and the loading amount of resol on the mesostructure of the carbons are systematically investigated. The small-angle X-ray scattering, nitrogen sorption and transmission electron microscopy results reveal that the resultant OMC in kilogram-scale quantities possesses high surface area (∼690 m2 g−1), large pore volume (∼0.45 cm3 g−1) and uniform, large pore size (∼4.5 nm) as well as thick pore walls (∼6.5 nm). The OMC exhibits good electrochemical performance of about 130 F g−1 in KOH electrolyte.  相似文献   

16.
The electrochemical insertion of sodium ions into different types of hard carbons was achieved in electrolytes composed of ethylene carbonate as the solvent and NaClO4 as the salt. For all the materials studied the sodium uptake increases when the carbon highest heat treatment temperature (HTT) decreases. PAN-based carbon fibres appear to be suitable structures to allow significant sodium insertion. Thus, T650 ex-PAN fibres lead to a reversible capacity close to 209 mAh g−1. In that case, sodium insertion occurs in two main ways: one is the adsorption on the single graphene layers and the other is the concomitant insertion into the porosity that occurs below 0.1 V versus Na+/Na. This second mechanism, which is indicated by a low-voltage plateau on the electrochemical curves, allows significant insertion. The compared electrochemical study of two saccharose-coke samples corresponding to different regions of Dahn's classification underlines the importance of the carbon precursor and of the manufacture process. The reversible capacity is equal to 184 mAh g−1 for the sample heat treated at 800 °C which presents a high hydrogen content whereas it is close to 145 mAh g−1 for the one characterized by a HTT of about 1500 °C and a low hydrogen content. The best electrochemical performances are obtained for pyrolyzed cellulose carbons. Indeed, the reversible capacity is about 279 mAh g−1. Outgassing these carbons at 950 °C results in such a decrease of the reversible capacity down to 145 mAh g−1. That can be related either to the thermal elimination of heteroelements or to modifications of the pore size distribution. Consequently, the most suitable hard carbon material for anodic applications in rechargeable sodium-ion batteries should both present a high residual hydrogen content and a significant microporosity.  相似文献   

17.
A series of large-pore mesoporous carbon materials with a three-dimensional wormhole framework structure were synthesized by nanocasting using mesoporous silica as a hard template. Samples of hard-template mesoporous silica with pore diameters from 3.08 to 6.43 nm, pore volumes from 0.59 to 1.02 cm3 g−1 and surface areas from 832 to 579 m2 g−1 were prepared from tetraethyl orthosilicate as the silica source and ionic liquid 1-butyl-3-methylimidazolium bromide as structure-directing agent through hydrothermal treatment at different temperatures (110–150 °C) followed by calcining at 550 °C. Subsequently, carbon materials with large pore diameters (2.76–6.70 nm), pore volumes (0.74–2.10 cm3 g−1) and high surface areas (1074–1276 m2 g−1) were synthesized using the various mesoporous silicas synthesized at the different hydrothermal temperatures as a hard-template. The carbon material obtained at a hydrothermal temperature of 150 °C possesses outstanding adsorbility for amaranth and methylene blue dyes.  相似文献   

18.
Bituminous coal-based activated carbon was modified by impregnation with melamine and heat treatment at 850 °C. Another sample was impregnated with melamine and urea and heat treated at 650 and 850 °C. Chemical and physical properties of the materials were determined using Boehm titration, thermal analysis, sorption of nitrogen and SEM with EDX. Then the H2S breakthrough capacity tests were carried out and the sorption capacity was calculated. The results revealed that carbons modified with nitrogen-containing species and heat-treated at 850 °C have a hydrogen sulfide removal capacity exceeding more then 10 times the capacity of unmodified sample. H2S on the surface of these materials is oxidized to sulfuric acid and elemental sulfur and stored in the pore system. New carbons are hypothesized to act as catalytic reactors promoting two different pathways of hydrogen sulfide oxidation in two different locations. In small micropores, where water is present, hydrogen sulfide dissociate to HS ions and those ions are oxidized to sulfur radicals and sulfur dioxide leading to the formation of sulfuric acid. In larger pores with incorporated nitrogen, basic sites promote dissociation and formation of sulfur polymers, which are resistant to further oxidation.  相似文献   

19.
A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N2 adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors, but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization. The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups and limited graphitizable properties, and in turn medium but almost constant capacitances.  相似文献   

20.
XPS and NMR studies of phosphoric acid activated carbons   总被引:4,自引:0,他引:4  
Chemical structure of phosphorus species in two series of polymer-based and fruit-stone-based carbons obtained by phosphoric acid activation at 400–1000 °C were investigated by XPS and solid state 31P-NMR and 13C-NMR. It has been shown that the most abundant and thus thermally stable phosphorus species in all investigated carbons is phosphate-like structure bound to carbon lattice via C-O-P bonding. Small contribution of phosphonates (C-P-O linkage) was observed by 31P NMR in carbons obtained at temperature range of 500–700 °C, phosphorus oxide was evidenced by XPS in carbon prepared at 900 °C and elemental phosphorus in carbon activated at 1000 °C.  相似文献   

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