Lignin as a skeleton for maintaining pore structures generated in activation of poplar wood with ZnCl2.

Lignin is a major component of many biomasses and its specific contribution towards pore development of activated carbon (AC) was investigated herein by conducting activation of poplar with varied content of lignin with ZnCl2 at 550 °C. The results showed that lignin is an important contributor to the mass yield of AC (29.1 % from poplar versus 21.9 % after removing lignin) and its interaction with derivatives of cellulose/hemicellulose could suppress gas formation. Elimination of steric hindrance via removing lignin enhanced intra- and inter-particle condensation of cellulose structures, which, however, did not remarkably enhance the specific surface area of the resulting AC (956.2 versus 815.7 m2 g-1 for that from activation of lignin). The specific surface area of AC from the direct activation of poplar was significantly higher (1605.5 m2 g-1), demonstrating synergistic effects between lignin and cellulose/hemicellulose on enhancing pore development. Lignin played the roles as skeleton for retaining pores generated and for suppressing intensive fusion of carbonaceous intermediates, minimizing collapse of nascent pores. Removal of lignin rendered AC oxygen-rich and hydrogen-rich feature but also reduced the degree of graphitization and crystallinity by the formation of more defective structures. The in-situ IR characterization of the activation processes showed that more aliphatic structures bearing -OH, -C-H, CO, and C-O-C were exposed after the removal of lignin, which, however, could not form rigid structures to reserve pores generated.