Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption

The objective of this study is to relate textural and surface characteristics of microporous activated carbon to their methane adsorption capacity. Oil palm shell was used as a raw material for the preparation of pore size controlled activated carbon adsorbents. The chemical treatment was followed by further physical activation with CO₂. Samples were treated with CO₂ flow at 850 °C by varying activation time to achieve different burn-off activated carbon. H₃PO₄ chemically activated samples under CO₂ blanket showed higher activation rates, surface area and micropore volume compared to other activation methods, though this sample did not present high methane adsorption. Moreover, it was shown that using small proportion of ZnCl₂ and H₃PO₄ creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities.     

The adsorption properties of surface modified activated carbon fibers for hydrogen storages

In this study, activated carbon fibers (ACFs) with high surface area and pore volume have been modified by Ni doping and fluorination. The surface modified ACFs were characterized by BET surface area, SEM/EDS, XRD, and Raman spectroscopy. The changes in pore structure and surface properties of these modified ACFs were correlated with hydrogen storage capabilities. After fluorination treatment, although the micropore volume of ACF was decreased, amounts of hydrogen storage were found to increase. Additionally, micropore volume on ACFs was found to be unchanged with Ni doping, hydrogen storage capacities were considerably increased due to the effect of catalytic activation of nickel. Though fluorination of ACFs increases hydrogen affinity, the effect of catalytic activation of nickel is more prominent, and thus led to better hydrogen storage. Hence, it was concluded that hydrogen storage capacity was related to micropore volumes, Pore size distribution (PSD) and surface properties of ACFs as well as specific surface areas.     

Avoiding structure degradation during activation of ordered mesoporous carbons

Hierarchical micro–mesoporous carbons with high porosity development and ordered structure were prepared. The innovative proposal consists in developing microporosity in ordered mesoporous carbon by chemical activation in template presence in order to minimize the structural damage. Thus, we have directly carried out the chemical activation of a mesoporous carbon/silica composite with KOH. The effect on mesoporous ordered structure of both KOH/carbon ratio and activation temperature has been studied. Following chemical activation the specific surface area is increased from 341 to 1757 m²/g and the micropore volume becomes almost six times larger than initial value. Although a slight widening of the mesopore distribution and an increase in the mesopore volume has been observed during activation, TEM and XRD results reveal an excellent conservation of the ordered mesoporous structure during activation even at conditions well above the limits that a CMK-3 type carbon can resist.     

水蒸气活化法制备椰壳活性炭的孔结构特征

以农林废弃物椰壳在600℃炭化2h后的炭化料为原料,以水蒸气为活化剂,研究了活化温度、活化时间、水蒸气用量对活性炭的比表面积、微孔容积和收率等的影响。结果表明：椰壳炭化料的比表面积仅为185m^2／g,且以中孔为主。在活化过程中,通过提高活化温度和水蒸气用量缩短了活化时间,扩宽了孔径;当水蒸气用量和活化温度较为适宜时,延长活化时间,有利于微孔的形成。活性炭的比表面积、总孔容积、微孔容积可达：1465m^2／g,0．9703cm^3/g,0．7519cm^2／g。并通过非定域密度函数理论（NLDFT）对活性炭的孔径分布进行了表征。     

磷酸活化法制备半纤维素基颗粒活性炭

以半纤维素的主要模型物木聚糖为原料,在不添加其他粘结剂的条件下,采用磷酸活化法制备半纤维素基颗粒活性炭。讨论了浸渍比和炭活化工艺对活性炭吸附性能和孔隙结构的影响。研究结果表明:浸渍比的增加,有利于颗粒活性炭的比表面积、亚甲基蓝吸附值、强度、总孔容积和中孔容积的提高。随着炭活化温度的升高,颗粒活性炭的碘吸附值、亚甲基蓝吸附值、比表面积、总孔容积和微孔容积呈下降的趋势,强度呈上升趋势。N₂吸附-脱附等温线和孔径分析表明,颗粒活性炭具有发达的微孔结构,炭活化温度的升高不利于孔隙结构的发达。     

中孑L分布活性炭的制备与表征

以酚醛树脂为前驱体,纳米SiO2为模板剂,采用模板炭化和钾碱活化工艺研制中孔率较高、比表面积较大的中孔炭（Mesoporous carbon,MC）,考察了活化温度、活化时间、树脂模板比等工艺参数对活性炭孔结构的影响。测试了活性炭N2的吸附等温线、孔径分布、比表面积,并通过扫描电子显微镜观察其微观结构。结果表明,较优工艺条件为：树脂模板比为2：1、活化温度850℃、活化时间3h,该条件下所得中孔炭中孔率达91．4％,比表面积为1501m^2·g^-1,总孔孔容1．38m^2·g^-1,为理想的窄孔径分布活性炭。     

Controlling the textural parameters of mesoporous carbon materials

The mesoporous carbon materials prepared by inorganic templating technique using mesoporous silica, SBA-15 as a template and sucrose as a carbon source, have been systematically investigated as a function of sucrose to mesoporous silica composition, with a special focus on controlling the mesoporous structure, surface morphology and the textural parameters such as specific surface area, specific pore volume and pore size distribution. All the materials have been unambiguously characterized by XRD, N₂ adsorption–desorption isotherms, high-resolution transmission electron microscopy, high-resolution field emission scanning electron microscopy, and Raman spectroscopy. It has been found that the porous structure, morphology and the textural parameters of the mesoporous carbons materials, CMK-3-x where x represent the sucrose to silica weight ratio, can be easily controlled by the simple adjustment of concentration of sucrose molecules. It has also been found that the specific surface area of the mesoporous carbon materials systematically increases with decreasing the sucrose to silica weight ratio. Moreover, the specific pore volume of the materials increases from 0.57 to 1.31 cm³/g with decreasing the sucrose to silica weight ratio from 5 to 1.25 and then decreases to 1.23 cm³/g for CMK-3-0.8. HRTEM and HR-FESEM also show a highly ordered pore structure and better surface morphology for CMK-3-1.25 as compared to other materials prepared in this study. Thus, it can be concluded that the sucrose to silica weight ratio of 1.25 is the best condition to prepare well ordered mesoporous carbon materials with good textural parameters, pore structure and narrow pore size distribution.     

KOH activation of ordered mesoporous carbons prepared by a soft-templating method and their enhanced electrochemical properties

Ordered mesoporous carbon (COU-2) was synthesized by a soft-templating method. The COU-2 mesoporous carbon was activated by using KOH to improve its porosity. The mesopore size of COU-2 was 5.5 nm and did not change by the KOH activation. But, the BET surface area of COU-2 largely increased from 694 to 1685 m²/g and total pore volume was increased from 0.54 to 0.94 cm³/g after the KOH activation. The large increase of micropore volume is due to the increase of the surface area. Electrochemical cyclic voltammetry measurements were conducted in aqueous (1 M sulfuric acid) and organic (1 M tetraethyl ammonium tetrafluoroborate/polypropylene carbonate) electrolyte solutions. The KOH-activated COU-2 carbon shows superior capacitances over the COU-2 carbon and a commercial microporous carbon both in aqueous and organic electrolyte solutions. These results suggest that the carbons having regularly-interconnected uniform mesopores and micropores in thin pore walls are desirable for the electrodes in electrochemical double-layer capacitors.     

油茶壳微孔活性炭的制备及表征

以油茶壳为原料,经炭化、KOH活化,制备微孔活性炭。考查了活化温度、活化时间和碱炭比对微孔活性炭碘吸附值和产率的影响,并采用正交试验优化了制备条件。研究结果表明：活化温度800℃、活化时间180 min、碱炭质量比3.5：1时,活性炭的碘吸附值达3 221 mg/g,产率51.2%。采用比表面积孔隙分析仪测定了氮气吸附/脱附等温线,计算得BET比表面积为1 755.72 m²/g,平均孔径为2.15 nm,总孔容为0.328 cm³/g,微孔孔容占总孔容的55.8%;SEM分析可见活性炭表面具有大量孔隙结构;FT-IR分析表明活化促进了—CH₃、—OH热解,活性炭中仍保存含氧官能团。     

Comparisons of pore properties and adsorption performance of KOH-activated and steam-activated carbons

Carbonaceous adsorbents with controllable pore sizes derived from carbonized pistachio shells (i.e., char) were prepared by the KOH activation and steam activation methods in this work. The pore properties including the BET surface area, pore volume, pore size distribution, and pore diameter of these activated carbons were characterized by the t-plot method based on N₂ adsorption isotherms. Through varying the KOH/char ratios from 0.5 to 3, the KOH-activated carbons exhibited BET surface areas ranging from 731 to 1687 m²/g with a similar micropore content (80–92%). The carbons activated by steam at 830 °C for 2 h had a BET surface area of 821 m²/g with the micropore content of 42%. The micropore/total pore volume ratio (V_micro/V_pore) and average pore size (D_pore) were independent of the KOH/char ratio, revealing that KOH activation is a powerful method in developing and controlling the number of micropores with a very similar pore size distribution. The adsorption equilibria and kinetics of methylene blue, basic brown 1, acid blue 74, 2,4-dichlorophenol, 4-chlorophenol, and phenol from water on all activated carbons at 30 °C were investigated to demonstrate the fact that adsorption of organics is not only dependent upon the BET surface area but is also determined by the relative size between pores and molecules. The adsorption isotherms were subjected to the model fitting according to Langmuir and Freudlich equations. By comparing the projected area of adsorbates, the surface coverage of phenols is about 3.6 times of that of dyes (based on unit gram of activated carbon). The Elovich equation was found to suitably describe the adsorption process of all KOH-activated carbons while the adsorption behavior on the steam-activated carbon was reasonably fitted with the intraparticle diffusion model.     

利用标准等温线分析活性炭的完全孔分布

利用我们从标准等温线性质发展的孔分布计算两个新方法——完全无模型孔分布计算法和改进的微孔分析法对有代表性的九个活性炭样品进行了完全孔分布分析.用吸附仪测量样品的低温氮吸附等温线,用Pickett方程关联了这些吸附等温线,发现n值在1.1—1.4之间.因常数C值在100—300之间,选用标准等温线n_2作为完全孔分布分析的依据.获得了总表面积、微孔的表面积和体积、非微孔的表面积和体积以及平均微孔水力半径等主要孔结构参数,并获得了所有样品的完全孔分布.两个比值SR和VR在0.9—1.1之间,结果是令人满意的.分析结果指出,DX-09-1-1,7S及J三个样品基本上全是微孔,而其余的炭毡及BPL炭样品都有相当数量的非微孔.这些结果说明,利用标准等温线进行活性炭样品的完全孔分布分析是实用的.     

Preparation and characterization of activated carbons for SO<Subscript>2</Subscript> adsorption from Taixi anthracite by physical activation with steam

Taixi anthracite was used as a precursor to prepare activated carbons (AC) for SO₂ adsorption from flue gas. In this work the activated carbons were prepared by physical activation with steam. Specifically, the effects of activation temperature and burn-off degree on the physico-chemical properties of the resulting AC samples were comparatively studied. The different types of pore volumes, pore size distributions and surface chemistries of the activated carbons on the SO₂ adsorption were also analyzed. The results show that the increasing burn-off leads to samples with continuous evolution of all types of pores except ultramicropore. The ultramicropore volume increases to a maximum of 0.169 cm³/g at around 50% burn-off and then decreases for 850 °C activation. At higher activation temperature, the micropore volume decreases and the mesopore structure develops to a certain extent. For all the resulting AC samples, the quantities of the basic surface sites always appear much higher than the amount of the acidic sites. The activated carbon prepared with higher micropore volume, smaller median pore diameter and higher quantities of the basic surface sites represents better SO₂ sorption property.     

Microstructures of PAN-ACF modified by catalytic benzene deposition

Benzene pyrolysis was successfully introduced to modify the pore size distributions (PSD) of polyacrylonitrile based activated carbon fibers (PAN-ACF) into a sharp distribution, at the presence of nickel catalyst. The microstructures of samples were studied by means of nitrogen adsorption, XRD, and SEM. The nitrogen isotherms were analyzed in detail using the routine BET method, α_s plot, DR equation, Horvath-Kawazoe (HK) equation, and regularized density functional theory (DFT), by which the surface area, micropore volume, and PSD were obtained. The results showed that the pore size of PAN-ACF can be effectively narrowed by catalytic benzene deposition and the PSD showed a unimodal nature, exhibiting potential behavior as a molecular sieve. A fraction residue of catalyst located in the ultramicropores can be washed by acid, resulting in increased BET surface area and micropore volume, which can also be confirmed by XRD and SEM measurements.     

熔纺Kraft硬木木质素基活性炭纤维的活化工艺及性能研究

以熔融纺丝制备的Kraft硬木木质素纤维(HKL)为原料,经炭化得到木质素基炭纤维(HKL-CF),再采用水蒸气活化法制备了活性炭纤维(HKL-ACF),通过红外光谱仪和扫描电镜研究了水蒸气活化对活性炭纤维化学结构和表面形貌的影响,采用全自动物理吸附仪、X射线衍射仪和拉曼光谱仪等研究了活化时间、活化温度和活化水蒸气流量对所制备活性炭纤维的比表面积、孔结构和微晶结构的影响规律。研究表明,水蒸气活化处理提高了活性炭纤维中的C—O和C＝C结构含量;随着活化时间的延长,活性炭纤维的比表面积增大,且随活化温度和水蒸气流量的提高呈现出先增大后减小的趋势;晶粒尺寸随着活化时间和温度的提高,逐渐变小,纤维表面的石墨化程度随活化时间的增加,逐渐变大;活化温度800 ℃,活化时间4 h,水蒸气流量1 mL/min下制备的活性炭纤维的BET比表面积最高可达2 081.34 m²/g,总孔容最大为1.60 cm³/g。     

Role of microporosity and surface functionality of activated carbon in methylene blue dye removal from water

Activated carbons have been prepared from jute stick by both chemical and physical activation methods using zinc chloride and steam, respectively. They were characterized by evaluating surface area, iodine number, pore size distribution, and concentration of surface functional groups. The chemically activated carbon largely featured micropore structure, while the physically activated carbon mainly featured macropore structure. The specific surface area of chemically and physically activated carbons was 2,325 and 723 m ² /g, while the iodine number was 2,105 and 815mg/g, respectively. The concentration of surface functional groups was determined by Boehm titration method, which suggested that different types of surface functional groups are randomly distributed on chemical activated carbons, while it is limited for physical activated carbon. The microporosity along with surface functional groups provided a unique property to chemically activated carbon to adsorb Methylene Blue dye to a large extent. The adsorption of dye was also affected by the adsorption parameters such as adsorption time, temperature and pH. Comparatively, higher temperature and pH significantly facilitated dye adsorption on chemically activated carbon.     

Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation

This work focused on the preparation of activated carbon from eucalyptus and wattle wood by physical activation with CO₂. The preparation process consisted of carbonization of the wood samples under the flow of N₂ at 400°C and 60 min followed by activating the derived chars with CO₂. The activation temperature was varied from 600 to 900°C and activation time from 60 to 300 min, giving char burn-off in the range of 20/2-83%. The effect of CO₂ concentration during activation was also studied. The porous properties of the resultant activated carbons were characterized based on the analysis of N2 adsorption isotherms at −196°C. Experimental results showed that surface area, micropore volume and total pore volume of the activated carbon increased with the increase in activation time and temperature with temperature exerting the larger effect. The activated carbons produced from eucalyptus and wattle wood had the BET surface area ranging from 460 to 1,490 m²/g and 430 to 1,030 m²/g, respectively. The optimum activation conditions that gave the maximum in surface area and total pore volume occurred at 900°C and 60 min for eucalyptus and 800°C and 300 min for wattle wood. Under the conditions tested, the obtained activated carbons were dominated with micropore structure (∼80% of total pore volume).     

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     

粘胶活性炭纤维的吸附性能及其孔结构表征

由化学药品磷酸盐催化处理的粘胶纤维在氮气气氛下于８２０℃下炭化,随后用水蒸汽活化制得粘胶活性炭纤维。采用液氮７７．４Ｋ下的吸附测定了该纤维的吸附等温线和常温下的静态苯吸附量以研究其吸附性能,并对其孔结构诸如比表面积、孔容、微孔容等进行了表征。     

吸附精制工艺对相变石蜡正构烷烃碳数分布的影响研究

采用活性炭作为吸附剂进行相变石蜡吸附精制工艺研究,利用气相色谱分析仪测定了相变石蜡的正构烷烃分布,研究了活性炭用量、吸附温度、吸附时间对正构烷烃分布的影响。采用自动吸附仪、差示扫描量热仪测定了活性炭的孔结构、比表面积和相变石蜡的热性能。结果表明,活性炭的BET总比表面积为1 718.49 m2/g,BJH平均孔径为3.162 9 nm,微孔体积为0.319 8 m3/g;相变石蜡经过吸附精制正构烷烃总量可以提高4%~6%,碳数不同的正构烷烃随吸附温度、吸附时间和活性炭用量的增加,含量变化趋势不同;吸附工艺为:活性炭用量8%,吸附温度120℃,吸附时间60 min时,正构烷烃含量为89.89%,提高了4.38%,相变潜热为164.9 J/g,提高了12.33%。     

溶胶-凝胶法制备中孔炭材料及其表征

以正硅酸乙酯为无机模板硅源，蔗糖为炭前驱物，采用溶胶-凝胶法制得了比表面积达1073．36m^2／g，孔径分布集中，平均孔径为2．75nm的中孔炭材料，并采用FT—IR、N2吸附、TG—DTA和XRD等分析手段对其进行了表征。