Activated carbon fibers (ACFs) were oxidized using both aqueous and nonaqueous treatments. As much as 29 wt % oxygen can be incorporated onto the pore surface in the form of phenolic hydroxyl, quinone, and carboxylic acid groups. The effect of oxidation on the pore size, pore volume, and the pore surface chemistry was thoroughly examined. The average micropore size is typically affected very little by aqueous oxidation while the micropore volume and surface area decreases with such a treatment. In contrast, the micropore size and micropore volume both increase with oxidation in air. Oxidation of the fibers produces surface chemistries in the pore that provide for enhanced adsorption of basic (ammonia) and polar (acetone) molecules at ambient and nonambient temperatures. The adsorption capacity of the oxidized fibers for acetone is modestly better than the untreated ACFs while the adsorption capacity for ammonia can increase up to 30 times compared to untreated ACFs. The pore surface chemical makeup was analyzed using elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS).
In this study, we have been exploring a new ion exchange material in the form of a fiber that could yield a number of important advantages over conventional ion exchange beads. In this approach, ion exchange fibers are prepared by 1) coating low-cost glass fiber substrates with a polystyrene/divinylbenzene oligomer, 2) curing, and 3) sulfonating. The sulfonation process and effects of varying degrees of crosslinking were characterized through diffuse reflectance infrared spectroscopy and acid-base neutralization titrations. Capacities of 4.7 meq/ g (on a per resin basis) were easily obtained. Kinetics experiments showed the contact efficiencies of the new systems were greatly improved over the traditional beads due to greater surface associated with the film morphology and shorter diffusion lengths. This translated into an order of magnitude increase in ion exchange rate. As a result of the thin coatings, the use of solvents prior to functionalization, and preswelling of the finished product prior to end-use were eliminated. Scanning electron microscopy was used to image the fibers and track their mechanical integrity through various stages of the process. Finally, repetitive regenerations proved the long-term stability of the spent fibers. Copyright
ZnCl 2 -activated polyacrylonitrile (PAN) coated onto a fiberglass substrate was prepared in N 2 at 450 uC. The porous and chemical structures were characterized by using N 2 adsorption at 77 K, XPS, FTIR, competitive adsorption of CO 2 /CH 4 and the adsorption of Cs + , Sr 2+ and Ag + . The activated PAN displays a high BET surface area up to 1012 m 2 g 21 , a broad mesopore size distribution as well as a major micropore size distribution. Up to 19.3 wt% of nitrogen, which is probably in the form of pyridinic and pyrrolic structures, is incorporated in the chemically activated PAN. HCl uptake results show that such a material has a higher amount of weakly basic functional groups compared to a commercially available ACF15. The activated PAN also exhibits a higher selectivity coefficient for CO 2 /CH 4 at STP and higher adsorption amounts for Cs + , Sr 2+ and Ag + than ACF15. It is proposed that nitrogen-containing, weakly basic functional groups positioned on the suitable-sized pore walls improve the adsorption ability of the activated PAN toward CO 2 , Cs + , Sr 2+ and Ag + .
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