Structural Characterization of Heat-Treated Activated Carbon Fibers

Pitch (PIT) and cellulose (CEL)-based activated carbon fibers (ACFs) were heated at 1473–3173 K under an Ar atmosphere. The N₂ adsorption, X-ray diffraction (XRD), and magnetic susceptibility of the heat-treated ACFs were measured. The specific surface area of ACF samples was determined by the subtracting pore effect (SPE) analysis using the N₂ adsorption isotherm.Both stacking height, Lc and stacking width, La of ACFs began to increase remarkably above 2000 K. The amounts of N₂ adsorption on PIT and CEL became nil by heating above 1773 K and 2073 K, respectively. The relationships between the heating temperature and the magnetic susceptibility of ACFs near room temperature were divided into three regions: below 1773 K, from 1773 K to 2473 K, and above 2473 K.The results from gas adsorption, X-ray diffraction and magnetic susceptibilities have been explained with respect to the changes taking place in these three regions.     

Synthesis of High Surface Area MgAl2O4 Nanopowder as Adsorbent for Leather Dye Removal

Abstract

MgAl₂O₄ nanopowder has been prepared by alkoxides hydrolysis with further calcination at temperature of 700°C. The adsorption of a leather dye, Direct Black 38, onto this material was investigated. The sample was characterized by X-ray-diffraction (XRD), N₂ adsorption–desorption isotherm and Fourier transform infrared spectroscopy. The results showed that sample present a pure phase, and the average nanocrystal size of 8 nm, the BET surface area is about 206.5 m² · g^?1 and total pore volume is about 1.44 cm³ · g^?1. Adsorption kinetics data were modeled by film and pore diffusion model. The experimental isotherm was described by the Langmuir model. MgAl₂O₄ nanopowder presented a great removal efficiency of leather dye by adsorption process, with a maximum adsorption capacity of 833 mg of dye per gram of adsorbent.     

Iodine adsorption and structure of activated carbons

Studies were conducted on the adsorption of iodine from saturated aqueous solutions and from saturated vapor by eight activated carbons of greatly diverse pore structures. Water adsorption data were used to determine the pore size distribution curves which provided both the distributions of the pore constriction (desorption) and cavity (adsorption) diameters. Adsorption from aqueous phase formed a unimolecular layer on the carbon surface while adsorption from saturated vapor produced pore-filling of micropores (pores less than 30 Å diameter) and surface coverage of the macropores. A great deal of steric interference was present because of the small difference in the diameter of iodine molecule (4.94 Å) relative to the 10–30 Å diameter pores. Good correlation was attained between adsorption and pore structure when corrections were made for the steric effect and the mean diameter distributions of the constrictions and cavities were used. The model for the iodine-on-carbon adsorption resembles packing of spheres into cylinders.     

Surface and pore structure of deoiled acid-and heat-treated spent bleaching clays

Samples of spent bleaching clay were deoiled by hexane, methanol, hexane-methanol, and supercritical CO₂ extractions. The deoiled clays were regenerated by acid and heat treatments. Nitrogen adsorption isotherms for these samples are type IV with hysteresis loops corresponding to type H3, indicating slit-shaped pores. Used deoiled and dried samples have smaller surface areas and pore volumes than unused clay. The surface areas and pore volumes increased after heat treatment. Acidified heat-treated deoiled samples have smaller surface areas and greater pore volumes than unused clay, except for the methanol-deoiled sample. Thus, heat and acid treatments removed substances adsorbed in the pores that were not removed by solvents or CO₂ extraction. This was confirmed from the ratios of the cumulative surface area/BET surface area, as well as analysis of the pore size distributions, which indicated an increase in mesopores with radii of between 25 and 100 Å. The t-plots showed that smaller pores with sizes between 7 and 25 Å, present originally in the unused clays, were closed by heat treatment. These pores were absent in the deoiled and the heat-treated samples except for the heat-treated sample that was deoiled by hexane followed by methanol. Smaller pores, accompanied by an increase in surface area, were also observed for all deoiled samples after acid and heat treatments.     

Greenhouse Gas Adsorptivity of Horn-Shaped Carbon Nanotubes over Nitrogen: Equilibrium Study

The synthesis of horn-shaped carbon nanotubes using carbon tetrachloride as carbon source was carried out by solvothermal method at 200°C for 2 h. The scanning and transmission electron microscopic characterization of the obtained product showed the formation of horn-shaped carbon nanotubes with irregular wall structure having inner diameter of ～105 nm and length of ～1 µm. The equilibrium gas adsorption properties of horn-shaped carbon nanotubes derived from carbon tetrachloride were successfully investigated for CO₂, CH₄, and N₂ at 288, 303, and 318 K. Horn-shaped carbon nanotubes possess better CO₂ adsorption capacity (2.53 mmol/g) with high capacity selectivity (14.7) and equilibrium selectivity (59.1) over N₂ at 288 K. The detailed adsorption study with estimation of physical parameters such as Henry's constant and heat of adsorption identifies the horn-shaped carbon nanotubes as a potential adsorbent material in the field of CO₂ storage and separation.     

Worm-hole structured mesoporous carbon monoliths synthesized with amphiphilic triblock copolymer

In the present work, mesoporous carbon monoliths with worm-hole structure had been synthesized through hydrothermal reaction by using amphiphilic triblock copolymer F127 and P123 as templates and resole as carbon precursor. Synthesis conditions, carbonization temperature and pore structure were studied by Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy and N₂ adsorption–desorption. The results indicated that the ideal pyrolysis temperature of the template is 450 °C. The organic ingredients were almost removed after further carbonized at 600 °C and the mesoporous carbon monoliths with worm-hole structure were obtained. The mesoporous carbon synthesized with P123 as single template exhibited larger pore size (6.6 nm), higher specific surface area (747 m² g^?1), lower pore ratio (45.9 %) in comparison with the mesoporous carbon synthesized with F127 as single template (with the corresponding value of 4.9 nm, 681 m² g^?1, 49.6 %, respectively), and also exhibited wider pore size distribution and lower structure regularity. Moreover, the higher mass ratio of template P123/resole induced similar pore size, larger specific surface area and lower pore ratio at the same synthesizing condition. It was also found that the textural structure of mesoporous carbon was affect by calcination atmosphere.     

Preparation and Characterization of Activated Carbon from Eucalyptus Sawdust I. Activated by NaOH

Eucalyptus sawdust was used as a precursor to prepare activated carbon using NaOH as a chemical activation agent. The effect of preparation conditions on the characteristics of the produced activated carbon used as an adsorbent was investigated. The performance of the activated carbon was characterized by N₂ adsorption–desorption isotherms, Brunauer–Emmett–Teller equation, Barett–Joyner–Halenda equation, scanning electron microscopy and Fourier transform infrared analysis. When the eucalyptus sawdust mass was 30.00 g, with particle sizes between 0.25 and 0.42 mm, and the sawdust was heated and charred before activation by NaOH, the optimized conditions for the preparation of activated carbon was found to be as follows: mass ratio of NaOH to eucalyptus sawdust, 1:2; activation time, 30 min; and activation temperature, 700 °C. The Iodine number and BET surface area of the produced activated carbon was 899 and 1.12 × 10³ m² g^?1, respectively, with a 13.3 % yield. Activated carbon exhibits adsorption isotherms of type IV. The total pore volume, micropore volume and average pore diameter were recorded as 0.636, 0.160 cm³ g^?1 and 2.27 nm, respectively. The pore structure of the activated carbon is mainly mesoporous. Carbonyl and hydroxyl groups may also exist on the activated carbon surface.     

Preparation of Activated Carbons from Tobacco Stems by Potassium Hydroxide Activation and Phosphine Adsorption

Activated carbon preparation from tobacco stems by KOH activation at different activation temperatures and KOH/char mass ratios were investigated in this study. The effects of preparation parameters on activated carbon pore structure, morphometrics, microcrystallinities, and surface functional groups were characterized by N₂ adsorption, SEM, XRD, and FTIR technologies, respectively. The optimum preparation condition of activated carbon was activation temperature of 850°C, and KOH/char mass ratio of 2. Under this condition, the BET surface area of 2215 m²/g, and the pore volume of 1.343 cm³/g can be obtained. Prepared activated carbon showed clearly honeycomb holes, and a predominated amorphous structure. With increase of activation temperature and KOH/char mass ratio, decrease of surface oxygen functional group, and aromatization of the carbon structure was found. The activated carbon was subject to PH₃ purification, and the maximum PH₃ adsorption capacity of 253 mg/g can be realized based on well prepared KOH-AC with modification of 2.5% Cu. It seems that the activated carbon produced from chemical activation of tobacco stem would be an effective and alternative adsorbent for PH₃ adsorption because of its high surface area, adsorption capacity, and low cost.     

Synthesis and characterization of mesoporous graphite carbon,and adsorption performance for benzene

In this paper, graphite carbon with a mesoporous structure was synthesized using the template–catalysis procedure with hydrated metal oxide nanoparticle as template and catalyst, phenol and formaldehyde as carbon source. XRD, Raman, BET and TEM analyses were performed to study the effluence of synthetic conditions on the structure of samples. The adsorption performances for benzene vapor were evaluated. The results show that CCo and CFe samples have mesoporous graphitized carbon structures. The molar amount of template to carbon source significantly affects the specific surface area, pore structure and adsorption–desorption performance. The specific surface area of CCo-1, with the best graphite structure, was 287.638 m²/g, the pore size was 19.075 nm, and the adsorption capacity for benzene vapor was 19.615 mmol/g. The synergistic effect between the cobalt element and graphite carbons affects the adsorption capacity of CCo-3, which was 34.643 mmol/g. However, the desorption efficiency was only 89 %, and the adsorption performance of CCo-3 material was degraded greatly after three times run.     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

CO<Subscript>2</Subscript> adsorption at high pressures in MCM-41 and derived alkali-containing samples: the role of the textural properties and chemical affinity

The adsorption properties of N₂ and CO₂ of MCM-41 and derived alkali-containing samples were analyzed over a wide range of pressures (up to ~4500 kPa) and temperatures (between 30 and 300 °C). The high-pressure and high-temperature experiments were carried out on pure MCM-41 and K- and Na-impregnated derived samples. It was analyzed the influence of pressure and temperature on the CO₂ capture capacity on pure and impregnated samples. The adsorption performance was correlated to the structure and textural properties of the materials using X-ray diffraction and N₂ adsorption–desorption measurements. The addition of an alkaline element changes the textural properties of the material increasing the pore size, which positively affected the CO₂ adsorption capacity of these materials at high pressure. In addition, the isosteric heats of adsorption gave information about the chemical affinity between the impregnated materials and CO₂. The CO₂ adsorption at ~ 4500 kPa for the samples with 5 wt% Na at 100 and 200 °C were 77.98 and 9.79 mmol g^?1, respectively, while the pure MCM-41 adsorbs only 8.92 mmol g^?1.     

Characterization of accessible and inaccessible pores in microporous carbons by a combination of adsorption and small angle neutron scattering

We determine the pore size distribution for five activated carbons (comprising carbide derived as well as commercial activated carbon samples) by the interpretation of experimental small angle neutron scattering (SANS) intensity profiles, based on the primary assumption of an infinitely dilute solution of hollow spherical particles. The interpretation yields the pore size distribution of the carbon samples that have predominantly micropore populations (size <20 Å), but not for carbons which have significant mesopore populations of sizes up to 48 Å and high mass fractal degrees. The pore size distribution (PSD) results based on SANS data reveal significant populations of micropores of size <6.1 Å, and mesopores of size >20 Å, which are not present in the PSD results based on adsorption isotherms of either Ar at 87 K or CO₂ 273 K. This inaccessible porosity becomes accessible to CO₂ and Ar on heat treatment, leading to increase in the adsorption based pore volume. However, the surface area does not commensurately increase, indicating the inaccessible microporosity to predominantly comprise surface defects and roughness that are removed on heat treatment or activation. This finding sheds the light onto the evolution of porosity of activated carbons during gasification or post synthesis-treatment.     

常温下沥青基活性炭纤维对NO的催化氧化性能

以4种比表面积不同的沥青基活性炭纤维为材料,研究了常温下对模拟空气气氛中体积分数为50×10^-6的NO的催化氧化性能,并采用氮吸附法、Raman光谱和红外光谱对活性炭纤维进行了表征。结果表明,活性炭纤维可将NO部分催化转化为NO₂,较低比表面积的活性炭纤维因为其较窄的孔径分布和较大的类石墨微晶而有利于对NO的催化氧化。     

Effect of Preparation Conditions on the Property Cu/AC Adsorbents for Phosphine Adsorption

Copper-based activated carbon adsorbents (Cu/AC) were prepared and used to investigate the effects of various copper precursors, impregnation solution concentration, and calcination temperature on phosphine (PH₃) adsorption removal from yellow phosphorus tail gas. N₂ adsorption isotherm and X-ray Diffraction (XRD) were used for characterizing the Cu/AC adsorbents. It can be seen that the Cu(N)/AC adsorbent prepared from the Cu(NO₃)₂ precursor has higher PH₃ breakthrough adsorption capacity than other three adsorbent because the surface copper status of it is mainly CuO. Fresh activated carbon requires an optimal impregnation solution concentration (0.05 mol/L) to reach this optimal PH₃ breakthrough adsorption capacity (78.62 mg/g). The result shows that the surface chemical characteristics (Cu content) of activated carbon is more important than the physical ones (specific surface or pore volume) for the PH₃ adsorption performance. When the calcination temperature is 350°C, the Cu(N)/AC adsorbent has the biggest PH₃ breakthrough adsorbed amount of 112.38 mg/g. The present study confirmed that the Cu/AC adsorbents would be one of the candidates for PH₃ adsorption removal from yellow phosphorus tail gas.     

Influences of heat-treatment on the microstructure and properties of silica–titania composite aerogels

Silica–titania composite aerogels were synthesized via ambient pressure drying by using water glass and titanium tetrachloride as raw materials. The influences of heat-treatment at different temperature with different heating rate on the microstructure and properties of the composite aerogels were investigated by differential thermal analyzer, Fourier transform infrared spectrometer, X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscope and transmission electron microscope analysis. The results indicate that the silica–titania composite aerogels heat-treated at 250 °C exhibited highest specific surface area, pore volume and average pore diameter. When the heat-treatment temperature was higher than 450 °C, the –CH₃ groups on the surface of silica–titania composite aerogels would transform into –OH groups gradually, and in the meantime, the composite aerogels network structure would be destroyed gradually and the crystallinity of TiO₂ would be improved with the increase of heat-treatment temperature. Particularly, heat-treatment at temperatures above 750 °C would cause serious damage to the network structure of the composite aerogels. The adsorption/photocatalytic activity experiments showed that the composite aerogels heat-treated at 550 °C exhibit highest darkroom adsorption efficiency, and the 650 °C-heat-treated samples exhibited highest efficiency for removing the Rhodamine B from water.     

A modified Stöber process for the production of mesoporous Sub 2 micron silica microspheres; applications in HPLC

Mesoporous silica microspheres in the 1–2 μm range with good size monodispersivity were synthesized by ammonia catalysed hydrolysis and condensation of tetraethylorthosilicate using methanol as solvent and cetyltrimethylammonium bromide as surfactant porogen. The mesopore diameter was subsequently expanded from <20 Å to ~200 Å by a postsynthesis hydrothermal treatment in a water–amine emulsion system followed by controlled dissolution in aqueous alkali. XRD, TEM, and N₂ sorption measurements were used to characterize pore properties. Particle size measurements in conjunction with SEM were used to establish morphology and size distribution. Preliminary chromatographic results are presented which demonstrate the applicability of these particles in High Performance Liquid Chromatography (HPLC). The particle size, porosity and chromatographic performance of the particles are compared to commercial HPLC silicas.     

Adsorption of Cu(II) from Aqueous Solution by Porous Mn3[Co(CN)6]2 · nH2O Nanospheres

Prussian blue analogue of porous Mn₃[Co(CN)₆]₂ · nH₂O nanospheres with a large surface area were prepared by simple mixing K₃[Co(CN)₆]₂ and manganous nitrate solution at room temperature. The morphology and structure of the prepared products were characterized by XRD, FE-SEM, TEM, and BET. The results indicated that the product was composed of nanospheres with the diameter of ～250 nm, which was of porous structure with the pore diameter in the 2.5–4 nm range. The adsorption behavior of Cu(II) ions from aqueous solution onto porous nanospheres was investigated as a function of parameters, such as the equilibrium time, the pH, the initial concentration, and the temperature. A maximum adsorption capacity of 140.85 mg g^?1 of Cu(II) was achieved. Due to the simple synthetic method and its high adsorption capacity, the porous nanospheres had the potential to be utilized as an effective adsorbent for Cu(II) removal.     

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N₂ adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO₂) uptake on the sorbents, kinetics of CO₂ adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO₂ adsorption capacity ~3.09 mmol g^?1 using 10% pre-humidified CO₂ at 75°C. The presence of moisture in flue gas showed a promoting effect in CO₂ sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO₂.     

PREPARATION AND TESTING OF CARBON/SILICALITE-1 COMPOSITE MEMBRANES

Methods for preparation of carbon/silicalite-1 composite membranes have been developed. First, silicalite-1 membranes were prepared by in-situ hydrothermal synthesis on both porous alumina and metal disks. Preparation of the carbon/silicalite-1 composite membranes was accomplished by polymerizing furfuryl alcohol on the surface of the silicalite-1 membrane, followed by carbonizing the polymer layer in an inert atmosphere at 773 K. The pure silicalite-1 membrane showed no selectivity for single gases, indicating the presence of intercrystalline diffusion and viscous flow as the dominant transport mechanism. The carbon/zeolite composite membrane exhibited ideal selectivities for He/N₂, CO₂/N₂, and N₂/CH₄ of 11.99, 17.12, and 3.58 at room temperature. No permeation of n-butane and i-butane for the composite membrane was detected up to temperatures of 453 K, indicating that the pore size for the composite membrane was approximately 0.4 nm. By carefully oxidizing the carbon layer in air at 623 K, the pore size of the composite membrane was adjusted such that n-butane permeation could be detected. No permeation of i-butane was apparent, suggesting that the pore size of the composite membrane had been enlarged to approximately 0.5 nm. Further oxidation of the carbon layer produced a finite n-/i-C₄H₄ ideal selectivity, indicating that the pore size of the membrane was now larger than 0.55 nm. Therefore, selective oxidation of the carbon layer can be used to control the pore size of the composite membrane.     

CO2 Adsorption by Modified Palm Shell Activated Carbon (PSAC) Via Chemical and Physical Activation and Metal Impregnation

The aim of this study was to verify the ability of nickel-impregnated palm shell activated carbon (PSAC) for CO₂ adsorption and compare its performance with the chemically and physically activated PSAC. Sodium hydroxide and CO₂ were used as activating agents for chemical and physical activation, respectively. Nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) was used as a precursor for metal impregnation. The effect of different chemical loadings (NaOH: 20–50 wt%), metal impregnation (Ni(NO₃)₂·6H₂O: 16–28 wt%), and heat treatment time (1–4 h) was studied as parameters. Adsorption capacity was calculated using breakthrough graphs. The effect of humidity on CO₂ adsorption and desorption of CO₂ was also investigated in this study. The results revealed that chemically modified PSAC yields the highest adsorption capacity (48.2 mg/g) compared to other methods of activation. Interestingly, it was found that the adsorption capacity of nickel-impregnated PSAC was similar to other types of metal-impregnated activated carbon. Humidity gave a negative effect on CO₂ adsorption. In summary, results showed that chemical activation is an efficient technique to modify PSAC for CO₂ adsorption.