Rayon-based Activated Carbon Fibers Research Articles

Aqueous phase adsorption of different sized molecules on activated carbon fibers: Effect of textural properties

The effect that the textural properties of rayon-based activated carbon fibers (ACFs), such as the BET surface area and pore size distribution (PSD), have on the adsorption of differently sized molecules, namely, brilliant yellow (BY), methyl orange (MO) and phenol (PH), was investigated in the aqueous phase. ACF samples with different BET areas and PSDs were produced by steam-activating carbonized fibers for different activation times (0.25, 0.5, and 1 h). The samples activated for 0.25 h were predominantly microporous, whereas those activated for relatively longer times contained hierarchical micro-mesopores. The adsorption capacities of the ACFs for the adsorbate increased with increasing BET surface area and pore volume, and ranged from 51 to 1306 mg/g depending on the textural properties of the ACFs and adsorbate size. The adsorption capacities of the hierarchical ACF samples followed the order BY > MO > PH. Interestingly, the number of molecules adsorbed by the ACFs followed the reverse order: PH > MO > BY. This anomaly was attributed to the increasing molecular weight of the PH, MO and BY molecules. The equilibrium adsorption data were described using the Langmuir isotherm. This study shows that suitable textural modifications to ACFs are required for the efficient aqueous phase removal of an adsorbate.

SEM and AFM Studies on the Surface and Cross Section Morphology of Rayon-Based Activated Carbon Fibers

The surface and cross section morphology of rayon-based carbon fibers (RCF) and the resulting rayon-based activated carbon fibers (RACF) were investigated through scanning electron microscopy and atomic force microscopy. It was found that the surface of RCF exhibited grooves and striations with the width ranging from 30 to 90 nm, and the striation distribution was about 25 bars per µm around the circumference. While on the RACF, lots of pores emerged on the surface and superficial cross section (about 1 ~ 2 µm to the surface), namely, the external section was porosity but the interior section was close-grained. It was detected that the pore sizes ranged from 50 to 550 nm and the approximate pore distribution was 10 pores in 1×1 µm2. Furthermore, the walls of pores were not smooth but consisted of continuous grains with the diameters about 30 nm.

Effect of alkali metal salt on the macropore structure of rayon-based activated carbon fibers

Macroporous Rayon-based activated carbon fibers (ACFs) were produced from Rayon precursors impregnated with alkali metal salt and Lewis acid followed by chemical activation or water vapor activation. The effect of pretreatment conditions such as the concentration of alkali metal salt and impregnation time on the properties of the resultant ACFs were investigated by scanning electron microscopy and physical adsorption. Results showed that the pore sizes and their distribution could be controlled by the concentration and impregnation time of the alkali metal salt. A novel ACF with abundant macropores and micropores and with high specific surface area was obtained by an optimum pretreatment with alkali metal salt.

Formaldehyde removal by Rayon-based activated carbon fibers modified by P-aminobenzoic acid

We impregnated Rayon-based activated carbon fibers (ACFs) by p-aminobenzoic acid (PABA) and systematically investigated their porous structure, surface chemistry, and formaldehyde removal behavior. Using standard nitrogen adsorption analysis, we found that the specific surface area, the micropore volume, and the total pore volume decreased with increasing concentration of PABA. Through elemental analysis and X-ray photoelectron spectroscopy, it was found that some nitrogen-containing functional groups presented on the surface of modified Rayon ACFs. The modified Rayon-based ACFs showed much higher adsorption capacity and longer breakthrough time for formaldehyde than did as-prepared Rayon-based ACF. We proposed that the improvement of formaldehyde removal by modified ACFs was attributed to the combined effects of physisorption contributed by pore structures and chemisorption contributed by the N-containing functional groups, whereas there was only physisorption between the as-prepared ACF and formaldehyde molecules.

Rayon-based activated carbon fibers treated with both alkali metal salt and Lewis acid

Rayon precursors marinated by mixture aqueous solution containing NaCl and H 3PO 4 are activated by steam for manufacture of activated carbon fibers (ACF) in this work. It is interesting to find that mesopores (2 nm < pore size < 50 nm) and even macropores (pore size > 50 nm) are greatly developed on ACF surface, which indicates that NaCl + H 3PO 4 aqueous solution is an effectual pore size-enlarging impregnant. The influences of the concentrations of NaCl and H 3PO 4 on the pore distribution and morphology of the resulting ACFs are respectively examined by scanning electron microscopy (SEM), revealing that the pore structure can be controlled through an appropriate ratio of NaCl and H 3PO 4 impregnation. As it has been demonstrated that the adsorptivity of the ACF is related to the fractal characteristics of the pore structure, the fractal structure of the meso/macropores in the ACF is analyzed by the small angle X-ray scattering (SAXS) method, providing the characteristics of volume, size distribution and fractal dimension ( D) of the pores, Finally BET analysis has confirmed that ACFs with abundant mesopores/macropores indeed exhibit highly effective adsorption capacity.

Characterization of microstructure and surface properties of heat-treated PAN-and rayon-based activated carbon fibers

Polyacrylonitrile- and rayon-based activated carbon fibers (ACFs), subject to heat treatment over 600–1,100°C under N2 flow, were investigated using a number of surface analytical methods, including N2 adsorption isotherm, elemental analysis, and X-ray photoelectron spectroscopy. The adsorption capacities of benzene, carbon tetrachloride, and water vapor on as-received and heat-treated ACFs were determined. Results show that the ACFs under study were highly microporous but heat-treated ACFs contained more mesopores in the range of 20–30 A for PAN-based and 30–45 A for rayon-based. It can be seen that the high-resolution αs plot provided valuable information about structure properties. The pore size distributions of ACFs gave insight into the pore development with heat treatment temperature. Besides, phenolic groups were found to be the most abundant oxygen-containing functional groups on the surface of both ACFs. The vapor adsorptions on ACFs indicated that molecular size and polarity of vapors, as well as the microstructure and chemistry of ACFs profoundly influenced the adsorption performance.

Surface chemistry of polyacrylonitrile- and rayon-based activated carbon fibers after post-heat treatment

Polyacrylonitrile- and rayon-based activated carbon fibers (ACFs) subject to heat treatment were investigated by means of elemental analyzer, and X-ray photoelectron spectroscopy (XPS). The total ash content of all ACFs was also analyzed. The adsorption of benzene, carbon tetrachloride and water vapor on ACFs was determined to shed light on the role of surface chemistry on gas adsorption. Results show that different precursors resulted in various elemental compositions and imposed diverse influence upon surface functionalities after heat treatment. The surface of heat-treated ACFs became more graphitic and hydrophobic. Three distinct peaks due to C, N, and O atoms were identified by XPS, and the high-resolution revealed the existence of several surface functionalities. The presence of nitride-like species, aromatic N-imines, or chemisorbed nitrogen oxides was found to be of great advantage to adsorption of water vapor or benzene, but the pyridine-N was not. Unstable complexes on the surface would hinder the fibers from adsorption of carbon tetrachloride. The rise in total ash content or hydrogen composition was of benefit to the access of water vapor. Modifications of ACFs by heat treatment have effectively improved adsorption performance.

Influence of heat treatment of rayon-based activated carbon fibers on the adsorption of formaldehyde

The influence of heat treatment of rayon-based activated carbon fibers on the adsorption behavior of formaldehyde was studied. Heat treatment in an inert atmosphere of nitrogen for rayon-based activated carbon fibers (ACFs) resulted in a significant increase in the adsorption capacities and prolongation of breakthrough time on removing of formaldehyde. The effect of different heat-treatment conditions on the adsorption characteristics was investigated. The porous structure parameters of the samples under study were investigated using nitrogen adsorption at the low temperature 77.4 K. The pore size distributions of the samples under study were calculated by density functional theory. With the aid of these analyses, the relationship between structure and adsorption properties of rayon-based ACFs for removing formaldehyde was revealed. Improvement of their performance in terms of adsorption selectivity and adsorption rate for formaldehyde were achieved by heat post-treatment in an inert atmosphere of nitrogen.

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.

Adsorption of trace polar methy-ethyl-ketone and non-polar benzene vapors on viscose rayon-based activated carbon fibers

The adsorption of polar methy-ethyl-ketone (MEK) and non-polar benzene vapors on viscose rayon-based activated carbon fiber (ACF) was investigated. The pore texture and surface composition of ACF were characterized by nitrogen adsorption at 77 K and X-ray photoelectron spectroscopy (XPS), respectively. Gas adsorption on the samples was measured by the gravimetric method and the Dubinin–Radushkevich (DR) equation was used to fit the experimental adsorption isotherms. The experimental results show that ACF with different pore texture and surface composition exhibited different adsorption and desorption behavior for polar and non-polar vapors. The effect of adsorbate polarity on the adsorption capacity at lower concentrations was more significant in the case of adsorbents with a smaller surface area. It was found that evacuation treatment greatly increased the adsorption rate.