Raman spectroscopic study of effect of steam and carbon dioxide activationon microstructure of polyacrylonitrile-based activated carbon fabrics

This work presents the different effects of steam and carbon dioxide activa tion on the microstructure of an oxidized polyacrylonitrile (PAN) fabric. A n investigation was conducted on a series of carbonized fabrics and two ser ies of activated carbon fabrics. The fabrics were activated by steam and ca rbon dioxide using heat-treatment temperatures of 900-1100 degreesC. Steam and carbon dioxide developed the microstructure initially present in the PA N-based activated carbon fabrics, but with different effects. These fabrics in the form of fabric and powder were examined by X-ray diffraction and Ra man spectrometry. This study indicated that carbon dioxide only reacted wit h the crystalline edges or the irregular carbon on the fiber surface and th at the inside structure of the fibers was not greatly affected. When the fa brics were activated using steam, water molecules reacted not only on the f iber surface but also with the carbon at the crystal edge and/or the nonreg ular carbon in the fibers, which led to communicating pore structures on th e surface and in the inner portions of the fiber. This activation also prom oted the denitrogenation reactions. Because of these structures and reactio ns, the activated carbon fabrics, which were activated by steam, had the hi ghest stacking height for carbon layer planes (L-c), the highest number of layer planes (L-c/d(002)), the highest oxygen content, the largest crystal size (L-a), and the highest density over the other samples. (C) 2001 John W iley & Sons, Inc.