Structural evolution of cellulose during carbonization and activation

Carbon samples were prepared from cellulose by carbonization under the nitrogen atmosphere and water steam activa-tion. Their structure and specific surface area during carbonation and activation processes were studied by thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and nitrogen adsorption at low temperature. The results show that groups in the cellulose molecular structure like C-OH, C-O-C and C-H are mostly pyrolyzed completely between 280-380℃. A few fragments or surface groups produced during pyrolysis decompose continuously above 380℃. Meanwhile, carbon atoms rearrange within the solid sample and form graphite crystallites. Carbonization temperature exerts a crucial influence on the microcrystalline carbon structure and pore structure. With the rise of carbonation temperature, the size of graphite crystallites increases and the pore structure develops, but the specific surface area of the carbon prepared first increases and then decreases, reaching maximum at 600℃. Carbonization time has less significant influence on the structures. With increasing activation time, non-crystalline carbon is oxidized, the specific surface area and total pore volume of the carbon sample increase simultaneously. However, a longer activation time causes that the original crystalline carbon structure is destroyed, the specific surface area and total pore volume of the carbon sample decrease. The porosity is mostly abundant when non-crystalline carbon is fully oxidized and the original crystalline carbon structure is not destroyed.