Chemically activated hydrochar as an effective adsorbent for volatile organic compounds (VOCs).

Hydrochars derived from hickory wood and peanut hull through hydrothermal carbonization were activated with H3PO4 and KOH to improve their performance as a volatile organic compound (VOC) adsorbent. Polar acetone and nonpolar cyclohexane were used as representative VOCs. The VOC adsorptive capacities of the activated hydrochars (50.57-159.66 mg⋅g-1) were greater than that of the nonactivated hydrochars (15.98-25.36 mg⋅g-1), which was mainly caused by the enlargement of surface area. The significant linear correlation (R2 = 0.984 on acetone, and R2 = 0.869 on cyclohexane) between BET surface areas of hydrochars and their VOC adsorption capacities, together with the obvious adsorption exothermal peak of differential scanning calorimetry curve confirmed physical adsorption as the dominating mechanism. Finally, the reusability of activated hydrochar was tested on H3PO4 activated hickory hydrochar (HHP), which had higher acetone and cyclohexane adsorption capacities. After five continuous adsorption desorption cycles, the adsorptive capacities of acetone and cyclohexane on HHP decreased by 6.2% and 7.8%, respectively. The slight decline in adsorption capacity confirmed the reusability of activated hydrochar as a VOC sorbent.