High selectivity of TiC-CDC for CO2/N2 separation

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.     

Preparation of porous carbons from petroleum coke by different activation methods

Porous carbons were prepared from Shengli petroleum coke (SPC) and Minxi petroleum coke (MPC) by different activation methods with H₂O, KOH and/or KOH+H₂O as active agents. The porous carbons were characterized by nitrogen adsorption at 77 K. It has been found that activation method and component of petroleum coke, of which different kinds of transitional metals on petroleum coke are crucial for preparing high quality porous carbons. Under the identical experimental conditions, the co-activation with KOH and H₂O as active agents in the same activation process, which has been rarely reported in literature, is the easiest method for the preparation of porous carbons with high surface area. The sequence of active agents in terms of difficulty in the preparation of porous carbons with high surface area is as follows: KOH+H₂O>KOH>H₂O. A drawback of KOH+H₂O activation in the preparation of porous carbon in this work is found to be its low carbon yield in comparison to KOH activation. Compared with the SPC coke, the MPC coke with higher contents of transitional metal and carbon and lower content of nitrogen is more suitable for making high surface area porous carbons, which is believed to be mainly due to the difference in the contents of transitional metals. Porous carbon with surface area around 2500–3000 m²/g and carbon yield about 25–30% has been obtained from MPC coke by KOH+H₂O activation with less KOH and shorter activation time in comparison to the traditional methods.     

Microporous carbons finely-tuned by cyclic high-pressure low-temperature oxidation and their use in electrochemical capacitors

Microporous carbons with a finely controlled porosity have been prepared from non-porous chars by cyclic oxidation/thermal desorption and further used in supercapacitor electrodes working in organic medium. The described activation method is shown to be effective for at least two types of non-porous carbons derived from sucrose and cellulose. The low temperature oxidation is realized by H₂O₂ at 200 °C and followed by thermal desorption of the surface functional groups at 900 °C under nitrogen flow. The porosity-forming procedure involves 4–5 oxidation/decomposition cycles, thus allowing a gradual adjustment of average pore size to that of ions making up the standard organic electrolyte ?1 mol L^?1 TEA⁺ BF₄^? in acetonitrile. The build-up of pore volume during the initial cycles proceeds essentially through the opening/formation and deepening of narrow micropores (L₀ ≈ 0.8 nm), whereas a slight pore widening appears to be the main outcome of further cycles. Due to the low burn-off of the overall process, the carbons are shown to form much denser coatings (0.71 g cm^?3) than a steam-activated carbon used in industrial supercapacitors (0.52 g cm^?3).     

Superior carbon-based CO2 adsorbents prepared from poplar anthers

A series of renewable nitrogen-containing granular porous carbons with developed porosities and controlled surface chemical properties were prepared from poplar anthers. The preparation conditions such as pre-carbonization and activation temperatures and KOH amount significantly influence the structures and chemical compositions of the porous carbons, the CO₂ adsorption capacities of which are highly dependent on their pore structures, surface areas, nitrogen contents and adsorption conditions. The sample with developed microporosity, especially with the pores between 0.43 and 1 nm and high nitrogen content shows high CO₂ adsorption capacity at 1 bar and 25 °C. In contrast, when the adsorption pressure is higher than 5 bar, its CO₂ adsorption capacity is dominated by its surface area, and more accurately by its pore volume. Irrespective of this, if the pressure was decreased to 0.1 bar, its CO₂ capture ability is closely correlated to its nitrogen content but not to its porosity. By optimizing the preparation conditions, a porous carbon with a surface area of 3322 m² g⁻¹ and a CO₂ adsorption capacity as high as 51.3 mmol g⁻¹ at 50 bar and 25 °C was prepared.     

Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide

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.     

Impregnation assisted synthesis of 3D nitrogen-doped porous carbon with high capacitance

Three-dimensional (3D) porous carbons with controlled mesopore and micropore structures were prepared through a simple and low-cost ultrasonic and impregnation assisted method from waste air-laid paper. The ammonia management was used to dope the 3D porous carbons with different types of nitrogen heteroatoms in a way that replaced carbon atoms. The N₂ adsorption–desorption characterization suggested that the nitrogen-doped carbons have a high surface area of 1470 m² g⁻¹ with the average pore diameter of 4.2 nm, which are conducive to form electric double layer under high current density. The resulting 3D carbon exhibited a higher capacitance at 296 F g⁻¹ in comparison with the nitrogen-free one at 252 F g⁻¹ in 6 M KOH electrolyte. Moreover, a high power density ca. 0.313 kW kg⁻¹ and energy density ca. 34.3 Wh kg⁻¹ were achieved in the ionic liquid ([EMIm]BF₄). The findings will open a new avenue to use waste materials for high-performance energy-storage devices.     

Preparation and carbon dioxide uptake capacity of N-doped porous carbon materials derived from direct carbonization of zeolitic imidazolate framework

The preparation, characterization and CO₂ uptake performance of N-doped porous carbon materials and composites derived from direct carbonization of ZIF-8 under various conditions are presented for the first time. It is found that the carbonization temperature has remarkable effect on the compositions, the textural properties and consequently the CO₂ adsorption capacities of the ZIF-derived porous materials. Changing the carbonization temperature from 600 to 1000 °C, the composites and the resulting porous carbon materials possess a tuneable nitrogen content in the range of 7.1–24.8 wt%, a surface area of 362–1466 m² g⁻¹ and a pore volume of 0.27–0.87 cm³ g⁻¹, where a significant proportion of the porosity is contributed by micropores. These N-doped porous composites and carbons exhibit excellent CO₂ uptake capacities up to 3.8 mmol g⁻¹ at 25 °C and 1 bar with a CO₂ adsorption energy up to 26 kJ mol⁻¹ at higher CO₂ coverages. The average adsorption energy for CO₂ is one of the highest ever reported for any porous carbon materials. Moreover, the influence of textural properties on CO₂ capture performance of the resulting porous adsorbents has been discussed, which may pave the way to further develop higher efficient CO₂ adsorbent materials.     

Colloidal templating synthesis and adsorption characteristics of microporous–mesoporous carbons from Kraft lignin

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.     

Preparation and one-step activation of microporous carbon nanofibers for use as supercapacitor electrodes

Microporous carbon nanofibers were prepared by electrospinning from resole-type phenolic resin, followed by one-step activation. KOH was utilized to tune the fiber diameter and improve porous texture. By adjusting KOH content in the spinning solution, the fiber diameter could be controlled in the range of 252–666 nm and the microporous volume and specific surface area could be greatly improved. The electrochemical measurements in 6 M KOH aqueous solution showed that the microporous carbon nanofibers possessed high specific capacitance, considerable rate performance, and superior specific surface capacitance to conventional microporous carbons. The maximal specific capacitance of 256 F g⁻¹ and high specific surface capacitance of 0.51 F m⁻² were achieved at 0.2 A g⁻¹. Furthermore, the specific capacitance could still remain 170 F g⁻¹ at 20 A g⁻¹ with the retention of 67%. Analysis showed that the high specific surface capacitance of the resultant carbons was mainly attributed to optimized pore size (0.7–1.2 nm) and the excellent rate performance should be principally due to the reduced ion transportation distance derived from the nanometer-scaled fibers.     

Enhancement of CO2 adsorption on phenolic resin-based mesoporous carbons by KOH activation

Carbons with high surface area and large volume of ultramicropores were synthesized for CO₂ adsorption. First, mesoporous carbons were produced by soft-templating method using triblock copolymer Pluronic F127 as a structure directing agent and formaldehyde and either phloroglucinol or resorcinol as carbon precursors. The resulting carbons were mainly mesoporous with well-developed surface area, large total pore volume, and only moderate CO₂ uptake. To improve CO₂ adsorption, these carbons were subjected to KOH activation to enhance their microporosity. Activated carbons showed 2–3-fold increase in the specific surface area, resulting from substantial development of microporosity (3–5-fold increase in the micropore volume). KOH activation resulted in enhanced CO₂ adsorption at 760 mmHg pressure: 4.4 mmol g⁻¹ at 25 °C, and 7 mmol g⁻¹ at 0 °C. This substantial increase in the CO₂ uptake was achieved due to the development of ultramicroporosity, which was shown to be beneficial for CO₂ physisorption at low pressures. The resulting materials were investigated using low-temperature nitrogen physisorption, CO₂ sorption, and small-angle powder X-ray diffraction. High CO₂ uptake and good cyclability (without noticeable loss in CO₂ uptake after five runs) render ultramicroporous carbons as efficient CO₂ adsorbents at ambient conditions.     

Nitrogen-doped porous carbons through KOH activation with superior performance in supercapacitors

A series of nitrogen-doped porous carbons are prepared through KOH activation of a nonporous nitrogen-enriched carbon which is synthesized by pyrolysis of the polymerized ethylenediamine and carbon tetrachloride. The porosity and nitrogen content of the nitrogen-doped porous carbons depend strongly on the weight ratio of KOH/carbon. As the weight ratio of KOH/carbon increases from 0.5 to 2, the specific surface area increases from 521 to 1913 m² g⁻¹, while the nitrogen content decreases from 10.8 to 1.1 wt.%. The nitrogen-doped porous carbon prepared with a moderate KOH/carbon weight ratio of 1, which possesses a balanced specific surface area (1463 m² g⁻¹) and nitrogen content (3.3 wt.%), exhibits the largest specific capacitance of 363 F g⁻¹ at a current density of 0.1 A g⁻¹ in 1 M H₂SO₄ aqueous electrolyte, attributed to the co-contribution of double-layer capacitance and pseudocapacitance. Moreover, it shows excellent rate capability (182 F g⁻¹ remained at 20 A g⁻¹) and good cycling stability (97% capacitance retention over 5000 cycles), making it a promising electrode material for supercapacitors.     

The influence of a hierarchical porous carbon network on the coherent dynamics of a nanoconfined room temperature ionic liquid: A neutron spin echo and atomistic simulation investigation

The molecular-scale dynamic properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or [C₄mim⁺][Tf₂N⁻], confined in hierarchical microporous–mesoporous carbon, were investigated using neutron spin echo (NSE) and molecular dynamics (MD) simulations. Both NSE and MD reveal pronounced slowing of the overall collective dynamics, including the presence of an immobilized fraction of RTIL at the pore wall, on the time scales of these approaches. A fraction of the dynamics, corresponding to RTIL inside 0.75 nm micropores located along the mesopore surfaces, are faster than those of RTIL in direct contact with the walls of 5.8 nm and 7.8 nm cylindrical mesopores. This behavior is ascribed to the near-surface confined-ion density fluctuations resulting from the ion–ion and ion–wall interactions between the micropores and mesopores as well as their confinement geometries. Strong micropore–RTIL interactions result in less-coordinated RTIL within the micropores than in the bulk fluid. Increasing temperature from 296 K to 353 K reduces the immobilized RTIL fraction and results in nearly an order of magnitude increase in the RTIL dynamics. The observed interfacial phenomena underscore the importance of tailoring the surface properties of porous carbons to achieve desirable electrolyte dynamic behavior, since this impacts the performance in applications such as electrical energy storage devices.     

Structural evolution of carbide-derived carbons upon vacuum annealing

Microstructure and surface moieties of porous carbons play a significant role in affecting their performance in a variety of applications. While it is well known that high-temperature treatments of porous carbons can influence the microstructure, no systematic studies have been done on carbide-derived carbons. We show that vacuum annealing increases the pore volume and specific surface area of titanium carbide-derived carbon with no significant change in the pore size up to 1500 °C. This treatment produces porous carbons with subnanometer porosity and a specific surface area up to 2000 m²/g, while treating the samples at temperatures above 1600 °C increases the pore size above 1 nm because of graphitization and collapse of the micropore structure. The results demonstrate that vacuum treatment can be used to further tune the pore structure and potentially the surface functionality of carbide-derived carbons for supercapacitor electrodes, gas chromatography, sorption, sensing and other applications. Vacuum annealing of carbide-derived carbon is therefore a suitable alternative to conventional microstructure modification methods, such as gas or liquid phase activation, which are subject to substantial sample loss and result in additional surface functionalization.     

The production of polycarbosilane-derived porous carbon fibers

When a C-rich polycarbosilane (PCS) fiber is pyrolyzed in the presence of KOH, a porous carbon fiber was obtained after acid washing. During the process, silicon was almost completely eliminated and a large microporosity was formed. The porous carbon fibers have a surface area of 1100 m²/g and an average pore size of 2.80 nm. These materials are called “organic-carbide-derived carbons”.     

Evaluation of carbon nanopores using large molecular probes in grand canonical Monte Carlo simulations and experiments

Nanopores (pores between 1 and 5 nm) have been the object of a great deal of attention because they can selectively adsorb relatively large molecules such as macromolecules and polymer molecules. Conventional methods for analyzing porous structures—such as N₂ adsorption measurements at 77 K—can be used to investigate microporous and mesoporous structures, but there is a lack of investigation of nanopores or the boundary between micropores (<2 nm) and mesopores (2–50 nm). Here, we propose the evaluation method of nanopores using a large probe molecule, SF₆. Grand canonical Monte Carlo simulations for N₂ and SF₆ suggested that SF₆ was adsorbed in 1.5–5 nm nanopores, while there was N₂ adsorption for the wide range of pore sizes. The SF₆ adsorption could therefore be used to confirm existence of the nanopores. To test this, we used single-walled carbon nanohorns as porous carbons with widely distributed pore size. SF₆ was well adsorbed only in the nanopores at 195 K, whereas N₂ adsorption was observed in all micropores and mesopores. This structural analysis of nanopores using a large-molecule probing method complements structural analyses using N₂ adsorption, as well as other techniques.     

Heteroatom-doped carbon gels from phenols and heterocyclic aldehydes: Sulfur-doped carbon xerogels

Sulfur-doped carbon xerogels were obtained through carbonization of resorcinol/2-thiophenecarboxaldehyde organic gels. The acid-catalyzed sol–gel polymerization of resorcinol and 2-thiophenecarboxaldehyde leads to organic gels whose morphology and texture is dependent on the amount of catalyst used. As a result, monolithic organic gels with sulfur content of up to 19.6 wt.% and easily tailored properties can be produced. After carbonization, a substantial amount of sulfur is retained and porous carbon xerogels with S-content of up to 10 wt.% are produced (at 800 °C). Depending on the sol–gel synthesis conditions, monolithic S-doped carbon xerogels with controllable and enhanced mesoporosity, surface areas of up to 670 m²/g and enhanced mechanical integrity were obtained. Additional KOH activation of the organic or carbon xerogels enables production of micro–mesoporous carbons with surface areas of up to 2550 m²/g while retaining over 5 wt.% of sulfur. Preliminary CO₂ adsorption measurements were performed. On the basis of resorcinol/2-thiophenecarboxaldehyde gel synthesis a more general approach towards heteroatom-doped carbon gels is proposed: sol–gel polymerization of phenols and heterocyclic aldehydes. Thus a variety of heteroatom-doped porous carbon materials with a tailored pore texture and morphology are available via this procedure.     

Chitosan derived nitrogen-doped microporous carbons for high performance CO2 capture

Nitrogen-doped microporous carbons were fabricated by a simple chemical activation strategy in which chitosan and K₂CO₃ were employed as the precursor and activation agent, respectively. The textural and chemical properties of the porous carbons could be easily tuned by changing the ratio of K₂CO₃/chitosan and activation temperature. Due to their large pore volume, well-defined microporosity and relatively high nitrogen content, these porous carbons were applied as adsorbents for CO₂ capture and demonstrated excellent CO₂ uptake performances. In particular, the sample prepared at 635 °C with K₂CO₃/chitosan ratio = 2 shows a CO₂ uptake as high as 3.86 mmol g⁻¹ at 25 °C, 1 atm. Furthermore, the CO₂ uptake remains almost constant in five consecutive adsorption–desorption cycles, indicating this material has great stability and recyclability as a CO₂ sorbent. In addition, an extraordinary separation selectivity against N₂ (CO₂/N₂ selectivity of ca. 21) was also observed.     

Potassium salt-assisted synthesis of highly microporous carbon spheres for CO2 adsorption

Highly microporous carbon spheres for CO₂ adsorption were prepared by using a slightly modified one-pot Stöber synthesis in the presence of potassium oxalate. Formaldehyde and resorcinol were used as carbon precursors, ammonia as a catalyst, and potassium oxalate as an activating agent. The resulting potassium salt-containing phenolic resin spheres were simultaneously carbonized and activated at 800 °C in flowing nitrogen. Carbonization of the aforementioned polymeric spheres was accompanied by their activation, which resulted in almost five-time higher specific surface area and total pore volume, and almost four-time higher micropore volume as compared to analogous properties of the carbon sample prepared without the salt. The proposed synthesis resulted in microporous carbon spheres having the surface area of 2130 m² g⁻¹, total pore volume of 1.10 cm³ g⁻¹, and the micropore volume of 0.78 cm³ g⁻¹, and led to the substantial enlargement of microporosity in these spheres, especially in relation to fine micropores (pores below 1 nm), which enhance CO₂ adsorption. These carbon spheres showed three-time higher volume of fine micropores, which resulted in the CO₂ adsorption of 6.6 mmol g⁻¹ at 0 °C and 1 atm.     

Preparation of porous Al2TiO5-Mullite ceramic by starch consolidation casting and its corrosion resistance characterization

Stabilized Al₂TiO₅ (AT)-mullite (M) porous ceramics were fabricated by starch consolidation casting using corn starch as curing agent and their microstructure, mechanical properties, pore size distribution and corrosion resistance were examined. Results showed that AT-M porous ceramic with the flexural strength of 11.5 MPa, apparent porosity of about 54.7% and pore size distribution in the range of 1–15 µm could be obtained with 10 wt% corn starch addition. Corrosion resistance results showed mass losses in hot H₂SO₄ solution and NaOH solution for 10 h to decreased from 1.03% to 0.36% and 4.39–2% when the calcination temperature increased from 1400 °C to 1450 °C, which proved these AT-M porous ceramics to possess an excellent corrosion resistance in acidic condition when calcined at 1450 °C.     

Fabrication of nitrogen-doped hierarchically porous carbons through a hybrid dual-template route for CO2 capture and haemoperfusion

Hierarchically porous carbon materials have many important technological applications; however, most of them were fabricated using either expensive materials or complicated procedures. Based on a general chelate-assisted multi-component co-assembly strategy, nitrogen-doped hierarchically porous carbon materials were fabricated by using Al-based composite and commercial triblock copolymer Pluronic F127 as co-templates, and natural banana peel as precursor. This versatile strategy allowed to easily achieve tunable surface area (700–2100 m² g⁻¹), pore volume (0.38–1.65 cm³ g⁻¹) and a narrow average mesoporous size of ca. 2.72–4.03 nm by simply varying the dosages of Al³⁺ and F127, and to attain high N content (4.54 wt%) in a large-scale fabrication system (2 L). X-ray photoelectron spectroscope characterization of the as-prepared sample revealed nitrogen atoms are mainly in the form of pyridinic nitrogen, quaternary nitrogen and pyridine-N-oxide. Importantly, these as-obtained carbon materials showed excellent performance in CO₂ capture and bilirubin removal with high adsorption capacities and selectivities. The present fabrication strategy is also applicable to the design of porous carbons doped with other elements by choosing appropriate biomass precursors.