A selective drug-release system consisting of surface-modified electrospun carbon fibers by oxy/fluorination

A selective drug-release system was prepared for a controlled drug release between hydrophobic and hydrophilic drugs by using a prepared membrane. A membrane was constructed by electrospun carbon fibers. A porous structure was created in the carbon fibers by chemical activation to reduce the initial drug-burst phenomenon by drug storage in the pores. The surface of the activated carbon fibers was modified by the addition of hydrophobic/hydrophilic functional groups by oxyfluorination or fluorination treatments to allow the selective release of mixed hydrophobic and hydrophilic drugs. The in vitro drug permeation was studied under various applied electric voltages. The initial drug-release phenomenon was reduced due to the storage effect by the improved pore structure, and the drug-release rate was controlled by the intensity of the applied electric voltage. In addition, selective drug release was observed with the presence of the hydrophobic or hydrophilic functional groups introduced through oxyfluorination or fluorination treatments.     

Thermal fluorination effects on carbon nanotubes for preparation of a high-performance gas sensor

A high-performance NO gas sensor was prepared by inducing thermal fluorination of carbon nanotube semiconductors. Thermal fluorination of multi-walled carbon nanotubes (MWCNTs) was carried out at various temperatures (100 ∼ 1000 °C) to investigate the effects of the reaction temperature. The mechanism of high-performance NO gas sensor electrode was shown to depend on the fluorination temperature in a way that can be divided into three regions, separated at 400 and 1000 °C. In the first temperature region, the induction of fluorine functional groups onto MWCNTs showed the opposite trend in electrical resistance change comparing with traditional p-type MWCNTs. In the second temperature region, the induced fluorine functional groups were attenuated by generated fluorinated carbon gases resulting in the decomposition of MWCNTs and the recovery of traditional p-type gas sensor behavior. In the highest temperature region above 1000 °C, reoriented carbon structure was observed, showing bent nanotubes produced from destruction by fluorination and subsequent reorientation due to the high temperature. The gas sensing responsiveness was significantly improved by the thermal fluorination, which causes electrophilic attraction, creates adsorption sites for target NO gases and improve hydrophobicity for gas sensing stability in humid condition. In conclusion, a high-performance gas sensor was obtained by thermal-fluorination of MWCNTs.     

Effects of improved porosity and electrical conductivity on pitch-based carbon nanofibers for high-performance gas sensors

Pitch-based carbon fibers with multi-walled carbon nanotubes (MWCNTs) were fabricated via an electrospinning method and used as gas sensor electrodes. The pitch-based carbon fibers were treated at various temperatures to investigate the effect of the reaction temperature. The electrospun fibers were thermally treated to produce carbon fibers, and the resulting material was chemically activated to increase the number of active sites for efficient gas adsorption. The activation process improved the porous structure by increasing the specific surface area by approximately 86-fold. Due to the improved porosity and electrical conductivity, gas adsorption sites were enlarged and electron transfer was improved, resulting in a high-performance NO gas sensor with improved sensitivity and rapid response time. The improved porosity was attributed to the chemical activation process, and the enhanced electrical conductivity was attributed to the heat treatment and the addition of MWCNTs.     

Synthesis and characterization of mesoporous electrospun carbon fibers derived from silica template

In our study, mesoporous carbon fibers were prepared by using electrospinning and physical activation. In order to develop mesoporous structure, silica was used as a physical activation agent due to meso-size of particle. The diameter of activated carbon fibers increased and surface became rougher after physical activation. Textural properties of carbon fibers were evaluated by using surface pore structure analysis apparatus. The specific surface area increased 12 times and total pore volume increased about 57 times through physical activation using silica. The development of mesoporous structure was confirmed by pore size distribution and fraction of micropore volume. From the DFT pore size distribution, it is sure that broad meso-sized porous carbon fibers were obtained from physical activation in our experiment. The fact that fractions of micropore volume are too low showing less than 2% by the results of total pore volume and HK pore volume concedes that silica activated CFs are pretty mesoporous. Eventually activated carbon fibers having broad meso-sized pores were obtained successfully.     

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.     

The improved electrical conductivity of carbon nanofibers by fluorinated MWCNTs

In order to increase the conductivity of carbon nanofiber sheet, conductive multi wall carbon nanotubes (MWCNTs) was added into the carbon fibers. The dispersion of MWCNTs into the fibers and adhesion between carbon fibers and MWCNTs were improved through fluorine modification on surface of MWCNTs. By fluorination treatment, hydrophobic functional group was introduced on the surface of MWCNTs improving the affinity on interface between two carbon materials. These nanofibers made by electrospinning method were treated at different temperature in order to investigate the effect of temperature. According to the increment of temperature, the better conductivity of carbon nanofibers sheet was obtained due to the better oriented carbon structure. Eventually, the improved conductivity of carbon nanofiber sheet was resulted showing 27 S/cm.     

Scanning electron microscopic studies of porous carbon electrodes used in alkaline fuel cells

Multilayer, polytetrafluoroethylene (PTFE)-bonded gas diffusion-type electrodes were prepared by the rolling method. Changing the electrode structure and manufacturing method improved alkaline fuel cell performance. Activated carbon or carbon black was used as the support material, with platinum as a catalyst and nickel screen as the backing material. Double-layer electrodes possessed both active and diffusion layers on the backing layer. However, the single-layer electrodes had only the active layer on the backing layer. The electrodes were prepared by using different PTFE contents and platinum loadings. In this study the surface photographs of the electrodes were taken with a scanning electron microscope. Elemental analyses of the surface elements were performed by energy dispersive X-ray spectroscopy (EDXS). Electrodes having activated carbon on their surfaces were observed to possess a nonuniform and porous structure. These electrodes showed better performance than electrodes having carbon black, which presented a uniform and nonporous structure.     

HEMP-derived activated carbon fibers by chemical activation with phosphoric acid

Activated carbon fibers were prepared by chemical activation of hemp fibers with phosphoric acid at different carbonization temperatures and impregnation ratios. Surface properties of the activated carbons fibers were significantly influenced by the activation temperature and the impregnation ratio. An increase of either of these parameters produced a high development of the porous structure of the fibers. Activated carbon fibers with apparent surface area of 1350 m²/g and mesopore volume of 1.25 cm³/g were obtained at 550 °C with an impregnation ratio of 3. The activated carbon fibers presented a high oxidation resistance, due to the presence of phosphorus compounds on the carbon surface. The oxidation resistance results suggest that C-O-PO₃ and mainly C-PO₃ and C-P groups act as a physical barrier, blocking the active carbon sites for the oxidation reaction.     

Surface Porosity of Lignin/PP Blend Carbon Fibers

Abstract

The surface porosities of carbon fibers derived from the polymer blend fibers of hardwood kraft lignin, HKL and polypropylene, PP, were discussed using thermal analyses, FTIR, and nitrogen adsorption. HKL/PP carbon fibers were prepared by two‐step thermal processing, thermostabilization, and carbonization. During the thermostabilization process, pores are created by oxidative degradation of the PP component. After thermostabilization some crystalline and highly oxidized PP components remained in the blend fiber. These residual PP components were subsequently pyrolyzed during carbonization, and effectively created a porous structure in the resulting carbon fibers. N₂ adsorption tests of the porous carbon fibers revealed the same type of adsorption/desorption isotherms as for activated carbon fiber. The internal surface area of the HKL/PP = 62.5/37.5 carbon fibers was calculated to be 499 m² g^?1. This value was lower than that for commercial activated carbon, 745 m² g^?1. However, these porous lignin‐based carbon fibers were not activated carbon fibers, which could be relatively easily done through steam activation. Thus, the HKL/PP blend carbon fibers appear to be promising precursors for activated carbon fibers.     

添加剂种类对活性炭纤维中孔结构的影响

纺制了含不同种类添加剂（金属氧化物、聚合物及炭素颗粒）的PAN原丝，经预氧化、炭化活化，制得了中扎含量不同的活性炭纤维，考察了添加剂种类对活性炭纤维中孔结构的影响，发现金属氧化物TiO2、Mgo，聚合物PVA、PVAc及炭黑均可明显提高最终活性炭纤维的中孔率。     

木质素纳米颗粒/天然纤维基活性碳纤维材料的制备及其电化学性能

以木质素纳米颗粒（LNPs）负载的天然纤维复合材料为研究对象,利用KOH活化的方法对其进行处理制备生物质基复合多孔活性碳纤维电极材料。随后在三电极体系中对合成的复合多孔活性碳纤维电极材料进行了电化学性能测试。研究表明,在0.5A/g的电流密度下,KOH活化的复合碳纤维电极材料的比电容为351.13F/g,远高于相同条件下未活化的复合碳纤维电极材料的比电容（7.88F/g）和未负载LNPs的天然纤维基活性碳纤维材料（306.50F/g）。而且在活化过程中,负载在纤维表面的LNPs会形成多孔的活性碳层结构,这会进一步提高复合活性碳纤维材料的循环稳定性,同时LNPs中丰富的羟基赋予复合材料额外的赝电容。在10A/g的电流密度下经过10000次循环后,复合活性碳纤维电极材料的电容保持率仍然为95%,高于未负载LNPs的活性碳纤维电极材料的电容保持率87%。结果表明,木质素纳米颗粒/天然纤维基活性碳纤维材料是一种理想的电极材料,本研究也为LNPs在生物质碳纤维作为储能电极材料的高值化应用提供了一条新途径。     

Conversion of polyacrylonitrile fibers to activated carbon fibers: Effect of activation

Polyacrylonitrile (PAN)-based activated carbon fibers were developed with the idea of increasing their potential and efficiency in industrial applications. The PAN-based fibers were first oxidized in air in a continuous multistage stabilization process, and then subjected to a continuous, low temperature carbonization and activation treatment in a mixture of steam and argon. The effect of the activation condition on the specific surface area, elemental composition, as well as the morphological structure of activated carbon fibers was studied. The surface area of the carbon fibers increased remarkably after the steam activation. It was found that steam activation promoted the elimination of nitrogen from the fiber. The bulk oxygen content of the fibers increased upon activation, probably due to formation of carbon-oxygen functionalities on the surface of the activated carbon fibers. The surface oxygen level of activated carbon fibers was greater than the bulk analysis of oxygen. It was observed that activation decayed the order of the carbon structure. © 1996 John Wiley & Sons, Inc.     

The electrochemical behavior of an enzyme biosensor electrode using an oxyfluorinated pitch-based carbon

A glucose sensor electrode was prepared by thermally treating a pitch-based carbon material. Oxyfluorination was used to modify the surface of the prepared carbon to induce the formation of hydrophilic functional groups. A glucose oxidase enzyme was effectively loaded onto the surface of the oxyfluorinated carbon and was more sensitive in glucose sensing because of the effects of the improved interfacial affinity between the electrode and the glucose oxidase. The introduced hydrophilic functional groups were examined using XPS analysis. In current–voltage measurements, a higher current was observed in the samples prepared with a higher oxygen content. In addition, a clear redox peak was observed in the surface modified samples. These results can be attributed to efficient electrical resistance measurement by easy electron transfer during glucose sensing. An efficient glucose sensor electrode was prepared using pitch-based carbon, which has beneficial electrical properties, and oxyfluorination, which improves the surface interface.     

Nitrogen and hydrogen adsorption of activated carbon fibers modified by fluorination

In this study, activated carbon fibers (ACFs) were surface modified with fluorine and mixed oxygen and fluorine gas to investigate the relationship between changes in surface properties by nitrogen and hydrogen adsorption capacity. The changes in surface properties of modified activated carbon fibers were investigated using X-ray photoelectron spectroscopy (XPS) and compared before and after surface treatment. The specific surface area and pore structures were characterized by the nitrogen adsorption isotherm at liquid nitrogen temperature. Hydrogen adsorption isotherms were obtained at 77 K and 1 bar by a volumetric method. The hydrogen adsorption capacity of fluorinated activated carbon fibers was the smallest of all samples. However, the bulk density in this sample was largest. This result could be explained by virial coefficients. The interaction of hydrogen-surface carbon increased with fluorination as the first virial coefficient. Also, the best fit adsorption model was found to explain the adsorption mechanism using a nonlinear curve fit. According to the goodness-of-fit, the Langmuir–Freundlich isotherm model was in good agreement with experimental data from this study.     

Novel vapor sensor from polymer-grafted carbon black: effects of heat-treatment and γ-ray radiation-treatment on the response of sensor material in cyclohexane vapor

Polyethylene (PE) was grafted onto carbon black surface by γ-ray radiation of the PE-adsorbed carbon black. Vapor sensor composite materials were prepared from the PE-grafted carbon black and PE as a matrix polymer. The effects of heat-treatment and γ-ray radiation-treatment on the response of the electric resistance of the sensor material against cyclohexane vapor were investigated. The heat-treatment of the composite improved the crystallinity of the matrix PE, and thus increased the responsiveness against cyclohexane vapor about five times that of the untreated one. The γ-ray radiation-treatment slightly decreased the responsiveness against cyclohexane vapor, because the γ-ray radiation-treatment induced the crosslinking of PE. On the contrary, the stability and reproducibility of the vapor sensor material remarkably improved. By the heat-treatment followed by the γ-ray radiation-treatment, a novel stable and reproducible sensor material was obtained, which allowed to identify and to quantify certain vapors in air accurately.     

NH4Cl改性活性炭脱除气态Hg0的特性分析

制备了原始活性炭与NH₄Cl改性活性炭,对其进行了物化特性表征,在固定床汞吸附实验台上考察了N₂气氛下颗粒粒径、NH₄Cl溶液浓度、SO₂、CO₂等因素对活性炭脱除Hg⁰性能的影响。研究结果表明：NH₄Cl浸渍改性没有造成活性炭孔隙结构的明显变化,但使得Cl元素成功担载到活性炭表面;随着颗粒粒径增大,活性炭吸附Hg⁰的外部传质速率、内部扩散速率均降低,较小的颗粒粒径有利于活性炭脱汞;由NH₄Cl改性在活性炭表面所产生的卤素官能团（AC-Cl）能够有效地氧化烟气中的Hg⁰,增强了活性炭对于Hg⁰的氧化吸附作用;SO₂能有限地促进原始活性炭的脱汞性能,对NH₄Cl改性活性炭脱汞性能则表现出先促进后抑制并主要体现抑制作用的现象,并且抑制作用随SO₂浓度的增大而增加;CO₂由于能在活性炭表面极化,且能与氨基官能团反应生成有利于吸附汞的羰基,促进了活性炭的脱汞性能。     

活性炭用于烟气脱硫的研究进展

活性炭材料因具有丰富的孔结构和较大的比表面积，而被用于大气污染治理。本文对活性炭材料用于烟气脱硫的研究现状(目前主要集中在含氧、含氮官能团的引入以及表面负载金属及其化合物的研究)进行了综述。最后展望了活性炭材料用于烟气脱硫的未来。     

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.     

具有多级孔道结构的高比表面多孔炭活化策略及VOCs吸附性能

以废弃榛壳为前体,采用不同活化策略制备多孔炭,探究活化策略和活化温度对多孔炭挥发性有机化合物（VOCs）吸附性能的影响,以及多孔炭的结构、表面性质与VOCs吸附性能的构效关系。结果表明,H₃PO₄法制备的多孔炭介孔体积大,且炭结构缺陷较少,吸附位点较少; KOH法获得的微孔体积较大,孔径集中在0.5~0.7nm的微孔,不利于VOCs分子吸附位点的有效利用。H₃PO₄-KOH分步法在850℃下制备具有高比表面积,孔径集中在0.5~1nm的宽微介孔分布,且炭结构高度无序并含有丰富缺陷位的多孔炭,为VOCs吸附提供了充足的吸附位点并提高了吸附位点了利用率,相比于H₃PO₄与KOH活化法制备的多孔炭的VOCs饱和吸附量显著提升,特别是对于弱极性VOCs。另外,H₃PO₄-KOH分步法制备的多孔炭表面官能团含量较低,极性较低,对非极性VOCs的吸附量远大于极性VOCs。因此,H₃PO₄-KOH分步活化策略是制备具有高比表面积、高VOCs吸附性能多孔炭的最优策略与方案。     

活性木质碳纤维的离子化研究进展

综述了活性木质碳纤维的离子化研究进展,归纳了有关粘胶基、剑麻基等木质活性碳纤维离子化的制备工艺及其晶体、含氧基团、孔隙和表面形态的结构特征与抗菌、脱硫和脱除NO_X方面的性能特点,在此基础上提出了存在的一些技术问题和今后开展科学研究的几点看法,重点在于加强负载不同金属木质活性碳纤维机理的研究,开拓离子化木质活性碳纤维的原料来源,完善其制备工艺和降低其成本。