Preparation of high-performance activated carbons from hemicellulose pre-extracted residues of poplar and their application in VOCs removal

Hemicellulose was pre-extracted from poplar by the KOH extraction method. A series of activated carbons with high VOCs adsorption capacity were prepared using hemicellulose pre-extraction residue (HPR) as carbon precursor and KOH as the activator. The results showed that the pre-extraction using organic solvent (benzene-ethanol mixture) had no significant effect on the hemicellulose removal efficiency and the microporous structure of activated carbons. After the selective pre-extraction of 38.2 to 65.7 wt% hemicellulose from poplar, the final yield of activated carbons only decreased by 1.1 to 2.0%, but the pore structure of activated carbons was greatly improved. A total of 40.7 wt% hemicellulose in poplar was removed under 4 wt% alkali concentration and 3 h KOH treatment. The activated carbons prepared from HPR of poplar gave the highest BET surface area (3066 m2·g-1) and pore volume (1.32 cm3·g-1). The pore structures of activated carbons can be controlled to some extent by changing the removal degree of hemicellulose. The activated carbon obtained under the optimized conditions showed excellent adsorption capacity for toluene (733 mg·g-1) and dichloromethane (184 mg·g-1). The correlation between adsorption properties and pore structure shows that the adsorption capacities of toluene and dichloromethane were closely related to micropores (＜ 2 nm) and ultramicropores (＜ 0.6 nm) of activated carbon, respectively. The pre-extraction of hemicellulose greatly improved the volatile organic compound (VOC) adsorption capacity of activated carbons by increasing the percentage of micropores.