An advanced method to manufacture hierarchically structured carbide-derived carbon monoliths

The preparation of carbide-derived carbon (CDC) monoliths with a hierarchically structure in the nm and μm range is presented. Basis is the manufacturing of porous cellular SiC ceramics based on a biomorphous approach with μm porosity and subsequent conformal conversion to CDC by reactive extraction with chlorine. The SiC ceramics can be sintered at low temperatures and short times (1500 °C, 2 h) compared to classical preparation methods. The SiC ceramics show a macro pore volume (1–10 μm channel size) of 0.56 ml g⁻¹, which corresponds to 1.5 ml g⁻¹ in the resulting CDC. The final carbon material exhibits an additional nano pore volume of 0.525 ml g⁻¹ with a mean slit pore size of 0.86 nm. Mechanical stabilities of the highly porous CDC are excellent (bending strength 2.1 ± 0.2 MPa, corrected Weibull modulus 8.7, characteristic strength 2.2 MPa and Youngs modulus 10.0 ± 0.5 GPa). The reactive extraction of the carbide monoliths shows very high reaction rates, approx. two dimensions faster (95×) compared to non-porous samples. Thus the manufacturing of the structured carbide and CDC can be performed at lower costs.     

Unique cyclic performance of post-treated carbide-derived carbon as an anode electrode

Carbide-derived carbon (CDC) is an attractive anode material for Li-ion battery applications because diverse pore textures and structures from amorphous to highly ordered graphite can be controlled by changing the synthesis conditions and precursor, respectively. To elucidate the unique cycling behavior of the post air-treated CDC anode, electrochemical performance was studied under variation of C-rates with structural changes before and after cycling. By tailoring the pore texture of CDCs as removal of amorphous phase by post air-activation, the anode electrode showed a high increase of capacity under prolonged cycling and under high C-rate conditions such as 0.3–1.0 C-rates. The discharge capacities of the treated CDC increased from 400 mAh g⁻¹ to 913 mAh g⁻¹ with increasing cycle number and were close to high initial irreversible value, 1250 mAh g⁻¹, at the 220th cycle under a 0.1C-rate condition, which are unique and unusual cyclic properties in carbon anode applications. Under high C-rate conditions, the discharge capacities started to increase from around 160 mAh g⁻¹ and values of 415 mAh g⁻¹, 372 mAh g⁻¹, and 336 mAh g⁻¹, were observed at 0.3, 0.5, and 1.0 C-rates, respectively, at 600 cycles, demonstrating stable capacity performance.     

The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents

The available adsorption working pairs applied to adsorption refrigeration system, which utilize activated carbon as adsorbent, are mainly activated carbon-methanol, activated carbon-ammonia, and composite adsorbent-ammonia. The adsorption properties and refrigeration application of these three types of adsorption working pairs are investigated. For the physical adsorbents, consolidated activated carbon showed best heat transfer performance, and activated carbon-methanol showed the best adsorption property because of the large refrigerant amount that can be adsorbed. For the composite adsorbents, the consolidated composite adsorbent with mass ratio of 4:1 between CaCl₂ and activated carbon, showed the highest cooling density when compared to the granular composite adsorbent and to the merely chemical adsorbent. The physical adsorption icemaker that employs consolidated activated carbon-methanol as working pair had the optimum coefficient of refrigeration performance (COP), volume cooling power density (SCP_v) and specific cooling power per kilogram adsorbent (SCP) of 0.125, 9.25 kW/m³ and 32.6 W/kg, respectively. The composite adsorption system that employs the consolidated composite adsorbent had a maximum COP, SCP_v and SCP of 0.35, 52.68 kW/m³ and 493.2 W/kg, respectively, for ice making mode. These results are improved by 1.8, 4.7 and 14 times, respectively, when compared to the results of the physical adsorption icemaker.     

Hierarchically porous graphitic carbon monoliths containing nickel nanoparticles as magnetically separable adsorbents for dyes

The hierarchically porous graphitic carbon monoliths containing nickel nanoparticles (HPGCM‐Ni) were fabricated via multi‐component co‐assembly in polyurethane (PU) foam scaffold associated with a direct carbonization process from triblock copolymer F127, diblock copolymer PDMS‐PEO, phenolic resol, and nickel nitrate and subsequent silicates removal with NaOH solution. The decomposable PU foam scaffold played important role in the process of multi‐component co‐assembly and macrostructure formation. The nickel salts were reduced to metallic Ni nanoparticles during the carbonization process. The obtained HPGCM‐Ni materials exhibited macropores of 100–450 μm, mesopore size of 7.2 nm, BET surface area of 725 m² g^?1, pore volume of 0.74 cm³ g^?1, and saturation magnetization of 2.3 emu g^?1. Using methyl orange as model dye pollutant in water, HPGCM‐Ni samples showed good adsorption capacity of 440 mg g^?1, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and separation under an external magnetic field. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41322.     

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures as excellent adsorbents for dyes

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures were synthesized through confinement self-assembly in polyurethane (PU) foam associated with a direct carbonization process from triblock copolymer F127, phenolic resol and ferric nitrate. It was observed that the magnetic Fe nanoparticles were embedded in the walls of graphitic porous carbon matrix, and the resulting materials exhibited hierarchically porous structure with macropores of 100–450 μm, mesopore size of 4.8 nm, BET surface area of 723 m²/g, pore volume of 0.46 cm³/g, and saturation magnetization of 3.1 emu/g. Using methylene blue as model dye pollutant in water, the carbon monolith materials showed high adsorption capacity of 190 mg/g, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and easy separation under an external magnetic field.     

Coal based magnetic activated carbon as a high performance adsorbent for methylene blue

Coal based magnetic activated carbons (MACs) were prepared by using the two-stage carbonization and activation of coal in the presence of Fe₂O₃ as the magnetic source. Compared with the single-stage carbonization and activation, the two-stage temperature method was found to be efficient for the preparation of MACs with the high specific surface area and good magnetic properties in a lower alkali/carbon ratio. The as-synthesized MACs at optimized conditions exhibited specific surface areas of up to 2075 m²/g and optimal saturation magnetization of as high as 15.02 emu/g. Moreover, as an adsorbent, the efficiency of removing methylene blue (MB) from aqueous solutions is excellent. Based on MB adsorption behaviors at various conditions, including initial dye concentration, contact time and temperature, MACs prepared at optimized conditions exhibited a maximum equilibrium MB adsorption capacity of 871 mg/g. The data of adsorption kinetics and isotherms could be well fitted by using the pseudo-second-order equation and the Freundlich model. Importantly, MACs can be separated and recovered easily by applying a magnetic field. Therefore, the coal-based magnetic activated carbons might be a promising candidate of high efficiency, low cost for removal of organic dyes.     

The preparation and performance of lignin-based activated carbon fiber adsorbents for treating gaseous streams

Two types of lignin-based carbon fibers were prepared by electrospinning method. The first was activated with Fe₃O₄ (LCF-Fe), and the second was not activated with Fe₃O₄ (LCF). Gas phase adsorption isotherms for toluene on LCF-Fe and LCF were studied. The gas phase adsorption isotherm for 0% RH showed LCF-Fe have about 439 mg/g adsorption capacity which was close to that of commercially available activated carbon (500 mg/g). The Dubinin-Radushkevich equation described the isotherm data very well. Competitive adsorption isotherms between water vapor and toluene were measured for their RH from 0 to 80%. The effect of humidity on toluene gas-phase adsorption was predicted by using the Okazaki et al. model. In addition, a constant pattern homogeneous surface diffusion model (CPHSDM) was used to predict the toluene breakthrough curve of continuous flow-packed columns containing LCF-Fe, and its capacity was 412 mg/g. Our study, which included material characterization, adsorption isotherms, kinetics, the impact of humidity and fixed bed performance modeling, demonstrated the suitability of lignin-based carbon fiber for volatile organic compound removal from gas streams.

Open image in new window

     

A carbide-derived carbon laminate used as a mechanoelectrical sensor

The mechanoelectrical effects attained through the enforced transfer of an ionic liquid through an electric double-layer capacitor-like laminate are described. The core component of the laminate is carbide-derived carbon, supported and separated by poly(vinylidene fluoride co-hexafluoropropylene). The different lateral sizes of the cations and anions of the ionic liquid electrolyte cause their different mobilities in the porous carbon structure. The judicious matching of the porosity of the carbon with the particular ionic liquid allows the formation of a diffusion potential solely by mechanical strain. Bending of this sheet-like laminate generates voltage and current; hence, it can be used as a motion sensor or as an energy harvesting unit.     

Adsorptive separation of carbon dioxide by polyethyleneimine modified adsorbents

Utilization of carbon dioxide (CO₂) has become an important global issue due to significant and continuous rise in atmospheric CO₂ concentrations. To find a potential solution, two types of mesoporous materials, MCM-41 and MCM-48, were synthesized and impregnated with 30, 50 and 70 wt% of polyethyleneimine (PEI) in methanol to evaluate the performance of the materials in terms of CO₂ adsorption. The materials were characterized by XRD, TGA, FTIR, TEM, SEM, N₂-physisorption and BET techniques. All the PEI-loaded materials exhibited substantially higher reversible CO₂ adsorption-desorption behaviors with >99% recovery. The above study proved that MCM-48 is a better material as compared to MCM-41 for loading of PEI. The material with 50 wt% loading of PEI on MCM-48, showed maximum adsorption of 248 mg/g-PEI at 80 °C which is about 30 times higher than that of MCM-48 and about 2.3 times that of pure PEI.     

Preparation and characterization of high surface area,high porosity carbon monoliths from pyrolyzed bovine bone and their performance as supercapacitor electrodes

Bovine cortical bone was pyrolyzed to produce a network of conductive carbon entwined with native hydroxyapatite that maintains its macroscopic structure during pyrolysis and prevents collapse of the carbon. Self-supporting conductive carbon monoliths were prepared by removing the hydroxyapatite with acid or ethylenediaminetetraacetic acid. The specific surface areas of these monoliths were determined by nitrogen adsorption, and their chemical structure was characterized using Raman spectroscopy. The monoliths exhibit specific surface areas and Raman spectra similar to those of amorphous carbons. Capacitance was assessed using the monoliths as the working electrodes in three-electrode cells, and two-electrode devices in which both electrodes were monoliths. Individual monoliths exhibit specific capacitances of 134 ± 11 F/g in aqueous solutions of potassium nitrate and 108 ± 9 F/g in the ionic liquid 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide. The capacitance of individual 6 mm diameter by 1 mm thick electrodes was typically on the order of 0.2 Farads.     

Development of carbon dioxide adsorbents using carbon materials prepared from coconut shell

Coconut shell, being a good carbon precursor and having a regular porous structure, was chosen for production of carbonic materials in this work. Metal doping on the coconut char was used to develop catalytic centers for hydrocarbon cracking and thereby obtain a product with good microporosity. Magnesium, calcium, cobalt, copper and nickel doping on the coconut char was done by soaking the coconut char in the aqueous solutions of the respective metal salt and further calcining. The characterization of the product samples was done by the measurement of surface area, adsorption capacity of CO₂, N₂, CH₄, and SEM analysis. The micro pore area obtained by using CO₂ adsorption at 298 K was found to be > 400 m²/g for samples prepared from coconut char impregnated with metal. The adsorption capacity of magnesium-doped sample was found to be 98 mg/g, whereas that for a sample prepared from non-impregnated coconut char was 55 mg/g. SEM analysis was conducted to study the morphology and nature of the samples prepared.     

Highly efficient adsorbents based on hierarchically macro/mesoporous carbon monoliths with strong hydrophobicity

Hierarchically porous carbon monoliths (HPCMs) with both ordered hexagonal mesoporosity and three-dimensionally connected macroporosity were synthesized via a simple and time-saving hydrothermal process followed by a nanocasting pathway. These monoliths have high macropore volumes and specific surface areas, strong hydrophobicity, low densities and regular shapes. Importantly, these HPCMs showed excellent performance in cleaning/recycling spilled oils or organic solvents with high adsorption capacity, rate, stability, and reusability, and in adsorbing bilirubin with high adsorption capacity, blood compatibility and durability in plasma as well. The adsorption of oil was based on the dispersion interaction between gasoline molecules and the carbon basal planes of HPCMs, while the isotherm of bilirubin adsorption on the optimized HPCMs and the corresponding kinetic data were found better fitted by Langmuir adsorption model and pseudo-second-order kinetic model, respectively.     

Uniaxially oriented carbon monoliths as supercapacitor electrodes

Cylindrical carbon monoliths of 7 mm in diameter and certain heights (1, 2, 3, 4 and 5 mm) are studied as model electrodes for supercapacitors. The monoliths show a narrow microporous structure with average micropore size of 0.73 nm and specific surface area of 1086 m² g⁻¹. The monoliths show straight walls and channels, both arranged along the cylinder axis. The former account for a remarkable electrical conductivity (6.5 S cm⁻¹ at room temperature). The latter allow a rapid ionic transport between the electrolyte bulk and the carbon walls and account for a high specific capacitance at high current density. The cell capacitance and resistance increase linearly with the monolith height according to C = (1.78 ± 0.06)h and ESR = (0.08 ± 0.01)h + (1.67 ± 0.04), respectively. The contribution of the electrolyte resistance, monolith resistance and monolith/collector resistance to ESR is discussed. The cell response time or constant time increases with the monolith height but according to a power dependence, τ = (4.5 ± 0.2)h^{(1.61 ± 0.03)}. The carbon of the monoliths show in KOH electrolyte a specific capacitance of 150 F g⁻¹ and a capacitance per surface area of 14 μF cm⁻².     

Preparation of titanium dioxide/activated carbon composites using supercritical carbon dioxide

The penetration of titanium tetraisopropoxide (TTIP) dissolved in supercritical CO₂ into the nano-spaces of an activated carbon was studied for the preparation of a TiO₂-coated activated carbon. The conversion of TTIP to TiO₂ through thermal decomposition was confirmed by evolved gas analysis during heat treatment under a N₂ flow. Acetone was detected in the evolved gas, which suggested that some isopropoxide groups in TTIP reacted with the carbonyl groups on the activated carbon surface. This chemical reaction with carbon is expected to be advantageous for favorable attachment to the carbon surface. The crystallite size of anatase in the TiO₂/carbon composites was 4.1 nm, as estimated from the X-ray diffraction pattern, which almost corresponded to the graphene crystallite size; L_a (3.3-3.4 nm), as estimated from both the Raman spectrum and X-ray diffraction pattern. As the size of the crystallite prepared by bulk condensation of TTIP was more than 15 nm, these results confirmed that the anatase crystals were present in the carbon pores. Also, it was suggested that the crystal growth of TiO₂ was influenced by the carbon nano-spaces.     

非金属氮掺杂活性炭催化剂制备及其催化CH4-CO2重整反应

采用硝酸和尿素联合对活性炭进行改性,制备了富含氮元素的氮掺杂活性炭,考察了孔结构、氮含量和氮种类（吡啶氮、吡咯氮和石墨氮）对CH₄-CO₂重整反应催化性能的影响。采用BET、SEM、EA、FTIR、XPS、CO₂-TPD和TG表征手段对反应前后催化剂的物理化学性质进行了表征,对引入活性炭表面的含氮官能团的种类及其在重整过程中所起的作用进行了分析。相比于未改性的原活性炭,硝酸和尿素同时改性制备的氮掺杂活性炭（AC-U.NA）引入了更多的羟基官能团和含氮官能团。特别是通过两者共同改性后,所制备的氮掺杂活性炭引入的吡啶氮官能团比例明显提高,为CH₄-CO₂重整反应提供了更多的活性位点,初始CH₄和CO₂转化率达到55.94%和66.46%。同时经过两者联合改性后,所制备的AC-U.NA材料表面具有极性,不仅有利于酸性CO₂分子的吸附和活化,而且有利于CO₂消碳反应,减少了积炭的生成,对所制备的非金属重整催化剂的活性和抗积炭性具有重要的意义。     

Carbon nanofibres and activated carbon nanofibres as electrodes in supercapacitors

Carbon nanofibres have been prepared by a floating catalyst procedure at industrial scale in a metallic furnace. The nanofibres (50-500 nm diameter and 5-200 μm length) are grown from the Fe particles used as catalyst. Soot appears together with the carbon nanofibres. The sample has been chemically activated using KOH as activating agent. Scanning electron microscopy has shown a smooth surface for the as-prepared carbon nanofibres but a rough surface for the activated ones. The specific surface area increases from 13 to 212 m²/g due to the activation. The volume of the micropores (in the 1-2 nm range) and the mesopores (2-5 nm range), as deduced by density functional theory methods, also increases after the activation. Electrochemical behaviour of the as-prepared and activated carbon nanofibres has been tested in a supercapacitor at laboratory scale using 6 M KOH aqueous solution as electrolyte. The specific capacitance, which is less than 1 F/g for the as-prepared sample, increase up to ≈60 F/g for the activated sample. Only a slight decrease in capacitance has been observed as the current density increases. Specific power of ≈100 W/kg at specific energy of 1 Wh/kg has been found in some particular cases. We have compared the electrochemical parameters of our activated carbon nanofibres with those of activated carbon nanofibres coming from a commercial sample; the latter was activated by the same way as our sample.     

Hierarchically porous sulfur-containing activated carbon monoliths via ice-templating and one-step pyrolysis

Hierarchically porous sulfur-containing activated carbons were prepared by ice-templating from an aqueous sodium poly(4-styrenesulfonate) (Na-PSS) solution followed by a single 800 °C pyrolysis step. This thermal treatment induced crosslinking, with the in-situ generation of Na₂SO₄ (activating agent), before carbonization and activation. The thermal treatment also resulted in the formation of sulfur salts, which could be converted to elemental sulfur upon a simple HCl acid wash. The sulfur content in the monoliths measured by microanalysis could be increased from 17.07 wt. % to 39.74 wt. % by incorporating additional Na₂SO₄ into the monoliths prior to pyrolysis. The sulfur was uniformly dispersed within the micropores of the carbon, and could be selectively removed by degassing (heating under vacuum) at different temperatures, revealing specific surface areas of up to 1051 m² g⁻¹. The materials were characterized by various techniques and were also evaluated for their potential as cathode materials for the lithium–sulfur battery. This work may open up new and facile routes to prepare sulfur-containing porous carbons for applications where its presence is beneficial.     

无机固体吸附剂在二氧化碳捕集应用中的研究进展

随着全球气候变暖,二氧化碳的捕集、利用和封存（CCUS）逐渐成为科学界和工业界的研究热点。CCUS的关键是选择性地从气体混合物中捕集二氧化碳。目前二氧化碳捕集技术包括化学吸收、膜分离、吸附和低温分离等。吸附法是利用吸附剂对不同气体的吸附能力差异来进行二氧化碳捕集。综述了分子筛、介孔二氧化硅、黏土及多孔碳等无机固体吸附剂在二氧化碳捕集应用中的研究进展。对比了不同改性方法对吸附剂吸附二氧化碳性能的影响。从应用角度来看,分子筛、介孔二氧化硅、黏土具有潜在的成本效益,但仍需在工程设计开发方面得以进一步发展,以适用于不同应用需求的二氧化碳捕集。     

Structure and performance of soy hull carbon adsorbents as affected by pyrolysis temperature

Soy hulls were evaluated as a source of adsorbent carbon for vegetable oil processing. Soy hull carbon was prepared by burning ground soy hulls (<100 mesh) at 300, 400, 500, or 700°C in a muffle furnace. The structure of the soy hull carbon was studied by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Crude soy oil was processed with the soy hull carbon products at 2% (w/w) in the laboratory under commercial bleaching conditions. Free fatty acids (FFA), peroxide value, phospholipid phosphorus (PLP), and lutein content of the treated samples were determined. SEM of the samples revealed particle size ranging from 1 to 2 mm. Increasing the pyrolysis temperature resulted in expansion and disruption of cellular structure. FTIR spectra of the carbon samples showed major differences in peak intensities at 3600 to 3200, 1600, and 1450 cm⁻¹ due to pyrolysis temperature. XRD revealed a predominantly amorphous structure with increasing pyrolysis temperature, which also resulted in an increased alkaline surface. Soy hull carbon decreased the FFA content of oil samples compared to that of crude oil, with the exception of carbon that was prepared at 300°C (P<0.05). A similar trend was observed in the adsorption of peroxides; however, no trends were observed in the adsorption of PLP or lutein. Higher pyrolysis temperature decreased randomness of the carbon and imparted a certain degree of structural order. This may be beneficial in providing physical access of the adsorbate molecule to the adsorbent surface.