Plasma Modification of Activated Carbon Fibers for Adsorption of SO_2

Viscose-based activated carbon fibers （VACFs） were treated by a dielectric-barrier discharge plasma under the feed gas of N2. The surface functional groups of VACFs were modified to improve the adsorption and catalysis capacity for SO2. The surface properties of the untreated and plasma-treated VACFs were diagnosed by SEM, BET, FTIR, and XPS, and the adsorption capacities of VACFs for SO2 were also compared and discussed. The results show that after the plasma treatment, the external surface of VACFs was etched and became rougher, while the surface area and the total pore volume decreased. FTIR and XPS revealed that nitrogen atoms were introduced onto the VACFs surface and the distribution of functional groups on the VACFs surface was changed remarkably. The adsorption characteristic of SO2 indicates that the plasmatreated VACFs have better adsorption capacity than the original VACFs due to the nitrogen functional groups and new functional groups formed in modification, which is beneficial to the adsorption of SO2.

Effects of Pre-oxidation Conditions on Adsorption Performance of Activated Carbon Fibers

In order to investigate the effects of pre-oxidation conditions on adsorption performance of activated carbon fibers （ ACFs ）, electrospun polyacrylonitrile （ PAN ） fiber webs were adopted as precursors for preparing ACFs. Firstly, the webs were stabilized under different pre-oxidation conditions; secondly, the pre-oxidative fibers were chemically activated by high temperature treatment in nitrogen. Pre-oxidation temperature, heating rate, and treatment time are the main factors on affecting the adsorption performance of the ACFs. Scanning electron microscope （ SEM）, differential scanning calorimeter （DSC）, and Fourier transform infrared spectroscopy （FTIR） were used to characterize the structure and property of the pre-oxldatlve fibers, and the dynamic benzene adsorption capacity of benzene of ACFs was measured. The results indicate that the moderate pre-oxidation condition is necessary to prepare the ACFs with better adsorption capacity, and the optimal oxidation conditions are to increase from room temperature to 230 ~C with a heating rate of 0.75 ~C ~ min -1 held at the peak temperature for 30min.

Structural Performance and Characterization of Polyimide Doped Activated Carbon Fibers for Mercury Adsorption

Structure characteristics about activated carbon fibers (ACF) and polyimide (P84) doped ACF modified by HNO3 solution were studied to apply in mercury removal in coal-fired flue gases. The P84, which was always used in the non-woven fabric for bag filter, was intermingled with polyacrylonitrile-based ACF (PAN-ACF) in the weight ratio of 1∶1 in order to make the doped ACF with P84 (doped-ACF-P84). Then the doped-ACF-P84 fibers were modified by HNO3 solution. The structure and morphology of doped-ACF-P84 were characterized and compared with those of ACF and doped-ACF-P84 modified by HNO3solution. The results show that the modified doped-ACF-P84 fibers have almost the same pore structure and specific surface area comparing with the original one. However, contrasted with the original PAN-ACF, the doped-ACF-P84 fibers modified by HNO3 solution have more oxygen-containing groups used for mercury removal. In particular, they have more lactone and carboxyl groups.

STUDY ON THE PROPERTIES OF DIFFERENT ACTIVATED CARBON FIBERS AND THEIR ADSORPTION CHARACTERISTICS FOR FORMALDEHYDE

Porous structure and surface chemistry of activated carbon fibers obtained by differ-ent precursors and activation methods were investigated. Adsorption isotherms werecharacterized by nitrogen adsorption at 77K over a relative pressure range from 10 6to 1. The regularization method according to Density Functional Theory (DFT) wasemployed to calculate the pore size distribution in the samples. Their specific surfaceareas were calculated by BET method, micropore volume and microporous specificsurface area calculated by t-plot method and MPD by Horvath-Kawazoe equation. Mi-cropore volume of rayon-based ACF was higher than that of other samples. The staticand dynamic adsorption capacity for formaldehyde on different ACFs was determined.The results show that steam activated Rayon-based A CFs had higher adsorption capac-ity than that of steam and KOH activated PAN-A CFs. Breakthrough curves illustratedthat Rayon-ACFs had longer breakthrough time, thus they possessed higher adsorp-tion capacity for formaldehyde than that of PAN-ACFs. The entire sample had smalladsorption capacity and short breakthrough time for water. Rayon-A CFs had exccl-lent adsorption selectivity for formaldehyde than PAN-ACFs. And the samples withhigh surface areas had relatively high adsorption capacity for formaldehyde. Elementaicontent of different A CFs were performed. Rayon-based A CFs contained more oxygenthan PAN-ACFs, which may be attributed to their excellent adsorption capacity forformaldehyde.

Fibrous TiO_2 prepared by chemical vapor deposition using activated carbon fibers as template via adsorption,hydrolysis and calcinations

TiO2 fibers were prepared via alternatively introducing water vapor and Ti precursor carried by N2 to an APCVD （chemical vapor deposition under atmospheric pressure） reactor at ≤200 ℃. Activated carbon fibers （ACFs） were used as templates for deposition and later removed by calcinations. The obtained catalysts were characterized by scanning electron micros- copy （SEM）, transmission electron microscopy （TEM）, Brunauer, Emmett and Teller （BET） and X-ray diffraction （XRD） analysis The pores within TiO2 fibers included micro-range and meso-range, e.g., 7 nm, and the specific surface areas for TiO2 fibers were 141 m^2/g and 148 m^2/g for samples deposited at 100 ℃ and 200℃ （using ACFI700 as template）, respectively. The deposition temperature significantly influenced TiO2 morphology. The special advantages of this technique for preparing porous nano-material include no consumption of organic solvent in the process and easy control of deposition conditions and speeds.

STUDIES ON THE CATALYTIC REACTION OF NITROGEN OXIDE ON METAL MODIFIED ACTIVATED CARBON FIBERS

The catalytic reaction of NO with CO and decomposition of NO over metal modified ACFs were investigated and compared with other carriers supported catalysts. It is demonstrated that Pd/ACF and Pd/Cu/ACF have high catalytic activity for the reaction of NO/CO, while Pt/ACF, Pt/Cu/ACF and Co/Cu/ACF have very low catalytic activity in similar circumstance. Pd-modified ACF possesses high catalytic decomposition of NO at 300℃. Pd/CB and Pd/GAC present good catalytic decomposition ability for NO only at low flowrate. Pd/G, Pd/ZMS and Pd/A however, do not show any catalytic activity for NO decomposition even at 400℃. Catalytic temperature, NO flowrate and loading of metal components affect the decomposition rate of NO. The coexistence of Cu with Pd on Cu/Pd/ACF leads to crystalline of palladium to more unperfected so as to that increase the catalytic activity.

PROGRESS ON ACTIVATED CARBON FIBERS

Activated carbon fiber is one kind of important adsorption materials. These novel fibrous adsorbents have high specific surface areas or abundant functional groups, which make them have greater adsorption/desorption rates and larger adsorption capacities than other adsorbents. They can be prepared as bundle, paper, cloth and felt to meet various technical requirement. They also show reduction property. In this paper the latest progress on the studies of the preparation and adsorption properties of activated carbon fibers is reviewed. The application of these materials in drinking water purification, environmental control, resource recovery, chemical industry, and in medicine and health care is also presented.

STUDY ON THE FACTORS AFFECTING REDUCTION CAPACITIES OF ACTIVATED CARBON FIBERS

The reduction adsorption of silver diamminonitrate on different kinds of activated carbon fibers (ACF) has been studied in this paper. The effect of different parameters, including adsorption temperature, concentrations of activation agents, and activation time on the silver adsorption capacities of activated carbon fibers has been investigated. The results show that higher temperature in which the silver complex interacts with ACF, or higher concentration of activation agent, will make higher reduction adsorption capacities of ACFs. More over, ACFs activated with phosphoric acid have higher reduction capacities than those activated with zinc chloride or steam.

PREPARATION OF ACTIVATED CARBON FIBERS AND THEIR XENON ADSORPTION PROPERTIES (I)-PREPARATION AND PORE STRUCTURE CHARACTERIZATION

A series of sisal based activated carbon fibers were prepared with steam activation at temperature from 750℃ to 900℃. Their pore structures were characterized through their nitrogen adsorption isotherms at 77K using different theories. The results showed that t-plot method and DR-plot method could suitably be used to characterize the mesopore structure and the multi-stage distribution of pore size of activated carbon fibers. It also showed that the pore size widens with the increase of activation temperature.

KINETICS OF DEPOSITION OF METAL IONS TO ACTIVATED CARBON FIBERS (ACFs) WITH FLUIDIZATION

The diffusion and mass transfer, reaction, integration and growth processes of the metal ions on the activated carbon fibers (ACFs) are discussed. Based on the diffusion film theory, the diffusion and the integration model are developed to describe the deposition processes of metal ions from the solution to ACFs in the fluidized beds. The model of heat transfer of this process is established to expound the important role-played in deposition processes by the influence of the reaction heat released at ACFs surface and the non-uniform temperature distribution caused by hydrodynamics.

STUDIES ON THE DYNAMIC COMPETITIVE ADSORPTION OF ORGANIC VAPORS ON THE ACTIVATED CARBON FIBERS ACTIVATED WITH PHOSPHORIC ACID

The dynamic competitive adsorption behaviors of different binary organic vapor mixtures on ACF-Ps under different operation conditions were investigated by gas chromatography in this paper. The studied mixtures included benzene/toluene, toluene/xylene, benzene/isopropylbenzene, ethyl acetate/toluene and benzene/ethyl acetate. Experimental results show that various ACF-Ps, as with ACF-W, can remove both vapors in binary vapor mixtures with over 99% of removal efficiency before the breakthrough point of the more weakly adsorbed vapor. In dynamic competitive adsorption, the more weakly adsorbed vapor not only penetrates early, but also will be displaced and desorbed consequently by stronger adsorbate and therefore produces a rolling up in the breakthrough curve. The ACF-Ps prepared at different temperatures have somewhat different adsorption selectivity. The feed concentration ratio of vapors, the length/diameter ratio and the thick of bed have effect on competitive adsorption. The competitive adsorption ability of a vapor is mainly related to its boiling point. Usually, the higher the boiling point, the stronger the vapor adsorbed on ACF-P.

STUDIES ON THE PREPARATION OF ZINC-CONTAINING ACTIVATED CARBON FIBERS AND THEIR ANTIBACTERIAL ACTIVITY

Several kinds of activated carbon fibers, using sisal fiber as precursors, were prepared with steam activation or with ZnCl2 activation. Zinc or its compounds were dispersed in them. The antibacterial activities of these activated carbon fibers were determined and compared. The research results showed that these sisal based activated carbon fibers supporting zinc have stronger antibacterial activity against Escherichia coli and S. aureus. The antibacterial activity is related to the precursors, the pyrolysis temperature, and the zinc content. In addition, small quantity of silver supported on zinc-containing ACFs will greatly enhance the antibacterial activity of ACFs.

STUDIES ON THE CHEMICAL STRUCTURES OFACTIVATED CARBON FIBERS BY SOLID STATE NMR

The solid stale C13-NMR spectra of different ACFs from various precursor fiberswere recorded in this paper. The effects of activation conditions on chemical structuresOf ACFs, as well as the changes of chemical structures during carbonization and redoxreaction were investigated by NMR technique. At same time, the solid state P31-NMRspectra of ACFs are studied The C13-NMR spectra of ACFs can be divided into sixbands that are assigned to methyl and methylene groups, hydroxyl and ether groups,acetal (or methylenedioxy carbon, graphite-like aromatic carbon structure, phenol,and quinone groups, respectively. Only phosphorous pentoxide exists on ACFs andCFs. Moreover, most of them are stuck over the crystal face but not at the edge ofgraphite-like micro-crystaL The carbonization and activation conditions affect theC13-NMR spectra of ACFs. The experimental results indicate that the redox reactionof ACFs with oxidants greatly consumes C-H group.

PREPARATION OF TiO_2 PHOTOCATALYST ANCHORED ON ACTIVATED CARBON FIBERS AND ITS PHOTODEGRADATION OF METHYLENE BLUE

TiO2 particulate photocatalyst anchored on activated carbon fibers (ACFs) was prepared by a molecular adsorption-deposition method. The TiO2 particles deposited on the carbon fibers formed a coating of about 100 nm in thickness. The photocatalyst prepared was characterized by means of SEM, EDS, XRD and UV-vis adsorption spec-troscopy. Anatase-type TiO2 was uniquely developed, and the micrographic structure of ACFs was not damaged during preparation. The roomy space between adjacent carbon fibers could allow UV-light to penetrate into the felt-form photocatalyst to a certain depth, so that a three dimensional environment was formed for the photocatalytic reaction. Such TiO2/ACFs photocatalyst exhibited its photocatalytic reactivity in photodegradation of concentrated methylene blue (MB) solutions. The MB molecules in the bulk solutions was supposed to be condensed around TiO2 particles by ad-sorption by ACFs. Therefore, the photocatalyst possesses the combined effect of adsorption by activated carbon fibers and photocatalytic reactivity of anatase-type TiO2 on MB photodegradation.

Characterization of TiO2 Loaded on Activated Carbon Fibers and Its Photocatalytic Reactivity

In this paper, TiO2 loaded on activated carbon fibers （ACF） was prepared by a coating treatment, followed by calcination at different temperatures in air atmosphere. The photocatalyst developed was characterized by SEM, XRD, XPS and UV-Vis adsorption spectroscopy. It was observed from SEM images that TiO2 loaded on ACF was in the form of small clusters with nanometer size. As confirmed by XRD and XPS determinations, the crystalline pattern of immobilized TiO2 was still anatase-form after calcination, and the micrographic structure and surface properties of ACF have not been damaged by the deposition process and calcination at different temperatures. Photocatalytic degradation of methylene blue （MB） in aqueous .solution was investigated using TiOE/ACF as photocatalyst. The comparison of photolysis, absorption and photocatalysis was carded out. The results indicated that the photocatalysis process of combined photocatalyst showed much higher degradation rate than that of photolysis and absorption processes. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed.

Adsorption Models and Structural Characterization for Activated Carbon Fibers

The nitrogen adsorption isotherms at 77.69 K were measured for two samples of activated carbon fibers and their microstructures were investigated. Among established isotherm equations, the Dubinin-Radushkevieh equation showed the best agreement with the experimental data, while the Langmuir equation showed a large deviation when employed at low relative pressures. The MP method, t-method and as-method were used to analyze the pore size distribution. The calculated average pore widths and BET （Brunauer-Emmett-Teller） surface areas for the sample A-13 were 0.86 nm and 1 286.60 m^2/g, while for the sample A-16, they were 0.82 nm and 1 490.64 m^2/g. The sample with larger pore width was more suitable to be used as additive in chemical heat pumps, while the other one could be used as adsorbent in adsorption refrigeration systems .

ADSORPTION OF DYES ON ACTIVATED CARBON FIBERS

The adsorplion behavior of dyes on a variety of sisal based activated carbonfibers (SACF) has been studied in this paper The results show that this kind of ACFhas excellent adsorption capacities for some organic (dye) molecules. SACF canremove nearly all methylene blue, crystal violet, bromophenol blue and Eriochromeblue black R from water after static adsorption for 24 h. at 30℃ The adsorptionamounts can reach more than 400 mg/g when adding 50 mg SACF into 50 ml dyesolution. Under the same conditions, the absorption amounts of xylenol orangefluorescein and Eriochrome black T were lower On the other hand, the adsorptionamounts change along with the characteristics of adsorbents. The SACFs activatedabove 840 ℃ which have higher specific surface areas and wider pore radii, havehigher adsorption amounts for the dyes. The researching results also show that foeadsorption rates of dyes onto SACFs decrease by the order of methylene blue,Eriochrome blue black R and crystal violet.

Preparation and Characterization of Activated Carbon Fiber from Paper

Activated carbon fibers （ACFS） with surface area of 1388 m2/g prepared from paper by chemical activation with KOH has been utilized as the adsorbent for the removal of methylene blue from aqueous solution. The experimental data were analyzed by Langmuir and Freundlich models of adsorption. The effects of pH value on the adsorption capacity of ACFS were also investigated. The rates of adsorption were found to conform to the kinetic model of Pseudo-second-order equation with high values of the correlation coefficients （R〉0.998）. The Langmuir isotherm was found to fit the experimental data better than the Feundlich isotherm over the whole concentration range. Maximum adsorption capacity of 520 mg/g at equilibrium was achieved. It was found that pH played a major role in the adsorption process, higher pH value favored the adsorption of MB.

Adsorption onto Activated Carbon Fiber Cloth and Electrothermal Desorption of Volatile Organic Compound(VOCs):A Specific Review

A general research program, focusing on activated carbon fiber cloths （ACFC） and felt for environmental protection was performed. The objectives were multiple： （i） a better understanding of the adsorption mecha- nisms of these kinds of materials; （ii） the specification and optimization of new processes using these adsorbents; （iii） the modeling of the adsorption of organic pollutants using both the usual and original approaches; （iv） applications of ACFC in industrial processes. The general question was： how can activated carbon fiber cloths and felts be used in air treatment processes for the protection of environment. In order to provide an answer, different approaches were adopted. The materials （ACFC） were characterized in terms of macro structure and internal porosity. Specific studies were performed to get the air flow pattern through the fabrics. Head loss data were generated and modeled as a fi.mction of air velocity. The performances of ACF to remove volatile organic compounds （VOCs） were approached with the adsorption isotherms and breakthrough curves in various operating conditions. Regenera- tion by Joule effect shows a homogenous heating of adsorber modules with rolled or pleated layers. Examples of industrial developments were presented showing an interesting technology for the removal of VOCs, such as dichloromethane, benzene, isopropyl alcohol and toluene, alone or in a complex mixture.