Defluorination-enhanced hydrogen adsorptivity of activated carbon fibers

Fluorinated activated carbon fibers (F-ACFs) were prepared by direct thermal fluorination of pristine activated carbon fibers. By the pyrolysis of F-ACFs at 1073 K under nitrogen gas flow, fluorine was subsequently eliminated and the sp²-bonded ACF structures were recovered. The micropore widths were 1.1 and 0.8 nm, and the isosteric heats of adsorption of nitrogen were 11.3 and 12.8 kJ/mol for pristine and defluorinated ACFs, respectively. These results strongly suggest that changes occurred in the structural properties of micropores in defluorinated ACFs. The hydrogen adsorption isotherms showed that the defluorinated ACFs adsorbed more hydrogen gas than pristine ACFs at 77 K, suggesting that the potential for interaction between hydrogen molecules and the defluorinated slit nanospaces was increased due to the changes in the pore structural properties and/or to the induced polarization of the pore walls making up the modified π-electron systems.     

The effect of embedded vanadium catalyst on activated electrospun CFs for hydrogen storage

In this paper, the effect of embedding vanadium pentoxide in electrospun carbon fiber was investigated in relation to textural properties and hydrogen storage behavior. Electrospun carbon fibers involving vanadium were prepared from polyacrylonitrile/N,N-dimethyl formamide/vanadium pentoxide through electrospinning method and heat treatment. Chemical activation of electrospun carbon fibers was carried out in order to generate the pore by using potassium hydroxide as a chemical agent. Eventually, vanadium embedded activated electrospun carbon fibers (AECFs) with high specific surface area 2780 m²/g were prepared as a hydrogen storage medium. As the effects of vanadium pentoxide, it was found that dissociated oxygen from vanadium pentoxide in electrospun fibers would generate the ultra-micropore (0.6 nm) by forming carbon monoxide and carbon dioxide during the carbonization. Also, vanadium in electrospun carbon fibers is considered to act as a catalyst for the improved capacity of hydrogen adsorption. Vanadium embedded AECFs have the high capacity of hydrogen storage, about 2.5 wt% at room temperature and 100 bar.     

改性活性碳纤维对苯胺吸附特性分析

开展了等离子体改性活性碳纤维对苯胺吸附性能的理论和实验研究。通过改变等离子体改性功率和改性时间,探寻最佳改性条件;采用BET、XPS、FTIR、热重测试对改性前后活性碳纤维理化特性进行了表征分析。结果表明,在等离子改性功率为22W,时间为3min时为最佳改性条件;改性后的活性碳纤维对水溶液中苯胺的去除率可达79.3%,去除率提高了8%。微观上等离子体改性使得活性碳纤维表面含氧官能团含量增加,增强对溶液中苯胺的吸附效果。吸附实验结果表明,改性前后活性碳纤维对苯胺的吸附在溶液pH为6时,吸附效果最佳;但达到同一去除率时改性活性碳纤维的速度更快,并且平衡吸附容量也更大。采用准一级和准二级动力学模型对该吸附过程进行描述,其改性前后均用准二级动力学拟合效果更好,表明活性碳纤维结构的特殊性使其对苯胺的吸附以化学吸附为主。活性碳纤维的等离子体改性提高了其对水溶液中苯胺的吸附速度和容量,增强去除效果降低了苯胺对环境的危害。     

Adsorption of nitrate onto nitrogen-doped activated carbon fibers prepared by chemical vapor deposition

Nitrogen-doped activated carbon fibers (ACFs) were prepared by chemical vapor deposition using melamine powder and acetonitrile for introducing quaternary nitrogen on the commercial ACFs, subsequently heated at 950 °C and activated by steam. Adsorption experiments of nitrate in aqueous solution were also conducted to evaluate adsorption capacity of the prepared ACFs using ion chromatography. The amount of introduced nitrogen content and nitrogen species on activated carbon fibers was examined by CHN elemental analyzer and X-ray photoelectron spectroscopy, respectively. As a result, adsorption capacity of quaternary nitrogen-doped ACF (ST-ML-AN-ST) was 0.75 mmol/g, indicating ca. two-times higher than that of untreated ACF (0.38 mmol/g). According to the adsorption data, the Langmuir isotherm model was the best fit. The prepared samples were also regenerated using hydrochloric acid. After regeneration, the adsorption capacity of the nitrogen-doped ACF (ST-ML-AN-ST) showed ca. 80% on average, implying that a portion of nitrates was adsorbed on the prepared ACFs irreversibly.     

表面改性活性炭吸附CS2及微波场中再生的研究

利用浸渍法探讨氧化物和含氮物质表面改性活性炭对CS2吸附性能的影响,通过boehm滴定和FT-IR分析结果证明:双氧水改性使活性炭表面碱性基团数增多,CS2动态吸附量增大;氨水和乙二胺改性活性炭,其表面碱性基团数增多,并引入含氮官能团,提高了CS2吸附容量。建立微波再生正交实验,确定微波再生最优实验条件:微波功率110 W、辐射时间2 min、载气流量250 mL/min时,活性炭再生综合率最大。对改性活性炭进行TG-DSC热分析,为活性炭微波热再生提供可靠参考依据。实验结果证明:双氧水、氨水、乙二胺改性可提高活性炭综合再生恢复率,硝酸改性对活性炭再生不利。     

Improvement of carbon materials performance by nitrogen functional groups in electrochemical capacitors in organic electrolyte at severe conditions

N-doped activated carbon fibers have been synthesized by using chemically polymerized aniline as source of nitrogen. Commercial activated carbon fibers (A20) were chemically modified with a thin film of polyaniline (PANI) inside the microporosity of the carbon fibers. The modified activated carbon fibers were carbonized at 600 and 800 °C, respectively. In this way, activated carbon fibers modified with surface nitrogen species were prepared in order to analyze their influence in the performance of electrochemical capacitors in organic electrolyte. Symmetric capacitors were made of activated carbon fibers and N-doped activated carbon fibers and tested in a two-electrode cell configuration, using triethylmethylammonium tetrafluoroborate/propylene carbonate (TEMA-BF₄/PC) as electrolyte. The effect of nitrogen species in the degradation or stabilization of the capacitor has been analyzed through floating durability tests using a high voltage charging (3.2 V). The results show higher stabilizing effect in carbonized samples (N-ACF) than in non-carbonized samples and pristine activated carbon fibers, which is attributed to the presence of aromatic nitrogen group, especially positively charged N-functional groups.     

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。     

The examination of surface chemistry and porosity of carbon nanostructured adsorbents for 1-naphthol removal from petrochemical wastewater streams

Chemically modified mesoporous carbon (CMMC) and chemically modified activated carbon (CMAC) were prepared by an acid surface modification method from mesoporous carbon (MC) and commercial activated carbon (AC) by wet impregnation method. The structural order and textural properties of the nanoporous materials were studied by XRD and nitrogen adsorption. The presence of carboxylic functional groups on the carbon surface was confirmed by FTIR analyses. Adsorption of 1-naphthol over various porous adsorbents such as CMMC, CMAC, MC and AC was studied. The adsorption isotherms of 1-naphthol were in agreement with a Langmuir model; moreover, the uptake capacity of 1-naphthol followed the order: CMMC>MC>CMAC>AC.     

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.     

沥青基活性碳纤维动态吸附甲苯的性能

以通用级沥青基碳纤维为原料,采用钴盐催化活化法,通过改变活化剂用量和活化时间制备出不同的活性碳纤维。研究了活性碳纤维的动态吸附甲苯以及再生性能。结果表明,活性碳纤维是一种优秀的甲苯吸附材料,其饱和吸附量受比表面积和孔径及其分布的影响。活性碳纤维对甲苯的动态吸附量达到1250 mg/g。20次吸脱附循环再生后,吸附量仍保持在900 mg/g。     

Study of the behavior of adsorbing CS2 by activated carbon

The adsorption of carbon disulfide on one raw and three modified activated carbon samples at different temperatures from 303 K to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus. The amounts of carbon disulfide adsorbed by three modified carbon samples are all larger than that of the raw one. It is found that organic amine is more effective than KOH as active ingredient for modification of activated carbon. The Freundlich equation is found to be the best model to fit the isotherm data for the four carbon samples at different temperatures studied.The isosteric heats of adsorption on the four carbon samples, derived from the adsorption isotherms using the Clapeyron equation, decrease with increase of surface loading. The heat of adsorption lies between 17.7 and 51.4 kJ/mol, where the carbon sample modified with KOH and ethylenediamine has the highest value with the exception of the case of high surface coverage (> 3.5 mmol/g). It is also found that the choice of adsorption isotherm has a significant influence on the values of isosteric heat of adsorption calculated. The isosteric heats of adsorption at zero surface loadings for the four carbon samples are 53.93, 53.87, 45.17 and 65.54 kJ/mol respectively and the carbon sample modified with KOH and ethylenediamine has the highest value. Analysis of the thermodynamic data shows the mobility of adsorbed carbon disulfide increases with increase of surface loading in all cases. The observed entropy change associated with the adsorption is higher than the theoretical value for the mobile adsorption but lower than the theoretical value for the localized adsorption in all cases except the carbon sample modified with KOH and ethylenediamine at higher surface coverage (> 4 mmol/g). The observed entropy change also decreases with increase of surface loading in all cases.     

基于分子动力学模拟的羟基改性调控活性炭对甲苯吸附性能的作用机理研究

本工作通过在六苯并苯分子边缘植入羟基构建不同羟基含量的改性活性炭,采用分子动力学和巨正则蒙特卡罗模拟研究了改性活性炭模型的物理性质、局部电荷和孔径分布,进一步分析了甲苯分子在改性活性炭中的动力学特性和吸附机理。结果表明,引入羟基可加强活性炭对甲苯的吸附能力。在较高相对压强下,羟基含量为39.4%是活性炭改性的最佳浓度,超过此浓度后甲苯的吸附量下降。改性活性炭羟基中强电负性的氧原子与甲苯甲基中的氢原子配合成Lewis酸碱对,形成稳定的吸附结构,进而增强活性炭对甲苯的吸附能力。在较低相对压强下,影响吸附量的主要因素为孔隙率和孔径大小;羟基含量为20.8%和31.4%的改性活性炭内多为微孔且结构较为紧密,使得其吸附甲苯效果较好。羟基改性使得甲苯分子在活性炭内的自扩散系数降低,且在含39.4%羟基的活性炭中扩散系数最低,这是由于甲苯分子与改性活性炭之间的非键相互作用阻碍了甲苯分子的运动。此外通过变温吸附研究发现,由于活性炭吸附甲苯过程具有放热性质,温度升高不利于甲苯的吸附。     

表面改性活性炭对CO_2的吸附性能

研究了用 H2 O2 ,HNO3加醋酸铜溶液进行表面改性后的活性炭对 CO2 的吸附性能 ,分析了改性前后活性炭的表面化学性质 ,测定了 2 73K下的吸附等温线 ,用 D- A方程对吸附等温线进行了很好的拟合 ,探讨了表面改性对活性炭表面化学性质的影响及其表面化学性质与吸附性能之间的关系。     

改性活性碳纤维对CO2的吸附性能

为了进一步提高活性碳纤维的CO₂吸附量和抗水性能,采用浸渍法将活性碳纤维进行改性处理,得到一系列改性样品,并对其进行了SEM和FTIR表征。研究了活性碳纤维种类、浸渍试剂（NaOH溶液、ZnCl₂溶液及离子液体）等对吸附剂孔结构、CO₂吸附量、循环使用性和抗水性能的影响,并探讨了CO₂在改性活性碳纤维内的动力学吸附扩散行为。研究结果表明：改性活性碳纤维的CO₂吸附性能和抗水性能均显著改善,其中CO₂最高吸附量达24.4%（0.1MPa和25℃）,吸湿率减小到1.33%,且具有良好的吸附/脱附循环使用性。均相扩散模型（HSDM）描述了实时吸附数据,此模型能够较好地反映CO₂在样品内的扩散行为,改性活性碳纤维仍能保持良好的扩散速率,扩散系数D_s值数量级为10^-5m²/s,与空白活性碳纤维相当。     

Low-cost metal oxide activated carbon prepared and modified by microwave heating method for hydrogen storage

Novel microporous activated carbon (MAC) with high surface area and pore volume has been synthesized by microwave heating. Iron oxide nanoparticles were loaded into MAC by using Fe(NO₃)₃·9H₂O followed by microwave irradiation for up to five minutes. The surface modified microporous activated carbon was characterized by BET, XRD, SEM and thermogravimetric examinations. Adsorption data of H₂ on the unmodified and modified MACs were collected with PCT method for a pressure range up to 120 bar at 303 K. Greater hydrogen adsorption was observed on the carbon adsorbents doped with 1.45 wt% of iron oxide nanoparticle loaded due to the joint properties of hydrogen adsorption on the carbon surface and the spill-over of hydrogen molecules into carbon structures.     

Effect of potassium-doping on the microstructure development in polyfurfuryl alcohol – derived activated carbon

Potassium-doped activated carbon was prepared by mixing potassium salt with polyfurfuryl alcohol precursor followed by carbonization and activation. Several experimental techniques, such as thermogravimetric analysis, gas adsorption, X-ray diffraction and Raman scattering spectroscopy were employed to understand the effects of potassium on the texture and pore structures of the activated carbon, which ultimately affects the hydrogen adsorption properties. After doping with potassium, the activated carbon exhibits higher surface area, higher micropore volume, and enhanced hydrogen adsorption capacity. Understanding of how alkali metals affect surface area and micropore development in activated carbon may help to clarify the hydrogen adsorption mechanism and improve the design of suitable carbon-based hydrogen storage materials.     

Effect of air oxidation of Rayon-based activated carbon fibers on the adsorption behavior for formaldehyde

The tailoring of pore surface chemistry of activated carbon fibers is shown to be an effective method for improving the adsorption efficiency of various volatile chemical compounds (VOCs). An oxidation treatment with air resulted in a significant increase in the adsorption capacities and breakthrough time for Rayon-based activated carbon fibers (ACFs) in removal of formaldehyde. The porous structure parameters of Rayon-based ACFs were determined with standard nitrogen adsorption analysis. The pore surface chemistry of samples under study was analyzed by Fourier Transform Infrared spectra (FTIR). Thus to some extent, the relationship between the adsorption properties, porous structure and pore surface chemistry was revealed.     

Hydrogen adsorption by nanostructured carbons synthesized by chemical activation

In this work several samples of Quercus agrifolia activated carbon, the porous structure of which was nanostructured by chemical activation with NaOH and KOH, were evaluated for hydrogen adsorption at 77 K and atmospheric pressure. Hydrogen adsorption reached values in the order of 2.7 wt.% for KOH activated carbon. The mechanism of formation of the porous nanostructures was found to be the key factor in controlling the hydrogen adsorption capacity of chemically activated carbon.     

Post-synthesis modifications of SBA-15 carbon replicas: Improving hydrogen storage by increasing microporous volume

SBA-15 carbon replicas were synthesized with a sucrose solution as carbon source, carrying out carbonization at two different temperatures (800 and 1000 °C). Carbon pyrolised at 800 °C showed higher BET surface area and was chosen for further post-synthesis activation treatments (physical via CO₂ or chemical via KOH), with the aim of improving hydrogen adsorption capacity. For comparison, an amorphous carbon was also synthesized, by direct carbonization of the carbon source, without any inorganic template: on this material a chemical activation was also performed. H₂ adsorption isotherms at the temperature of liquid nitrogen and sub-atmospheric pressure were measured. A linear correlation was found between hydrogen uptake and microporous volume of the different carbons, rather than with BET specific surface area. Surprisingly, the sample prepared in the absence of inorganic template resulted the most effective one.     

酸、碱改性活性炭对甲醇、甲苯吸附性能

分别采用硝酸和氢氧化钠对活性炭进行改性,利用比表面积及孔径分析仪（BET）、扫描电镜（SEM）、Boehm滴定法对活性炭物化性质进行表征,测试改性活性炭对甲醇、甲苯吸附性能。结果表明,经过酸、碱改性后的活性炭比表面积、总孔容、微孔孔容均有所增大。酸改性表面酸性基团增加,碱改性后活性炭酸性基团减少。酸改性后的活性炭对甲醇、甲苯吸附能力有所下降,后经碱改性的活性炭吸附能力均有不同程度的提高。单组分吸附实验时,甲醇穿透曲线斜率要大于甲苯,穿透时间早于甲苯。在多组分吸附过程中会出现甲苯取代甲醇的吸附现象,使得已经被吸附的甲醇发生脱附,此时甲醇的出口浓度大于进口浓度,形成峰值效应。