Enhanced adsorption performance and governing mechanisms of ball-milled biochar for the removal of volatile organic compounds (VOCs)

Hickory wood was pyrolyzed at 300 °C, 450 °C, and 600 °C to produce biochars, which were then modified by ball milling. The pristine and ball-milled biochars were used to remove volatile organic compounds (VOCs) including acetone, ethanol, chloroform, cyclohexane, and toluene. Compared with the corresponding pristine one, each ball-milled biochar showed significantly improved structural characteristics. Their specific surface area (SSA) increased by 1.4–29.1 times, average pore size (APS) decreased slightly, and the hydrophilicity and polarity were also enhanced according to the elemental analysis. The adsorption of VOCs by ball-milled biochar increased by 1.3–13.0 folds, and the maximum adsorption capacity of acetone was up to 103.4 mg/g. The adsorption of polar VOCs (acetone, ethanol, and chloroform) onto ball-milled biochars was mainly controlled by surface adsorption process, which was affected by the SSA, APS, and volatile organic matter of the biochars, as well as the properties of the VOCs. The adsorbed VOCs were completely desorbed from the ball-milled biochars at relatively low temperature (≤115.2 °C). Reusability experiments with five adsorption-desorption cycles showed that ball-milled biochar had an excellent reusability for all VOCs. Ball-milled biochars can therefore be used as an effective and regenerable adsorbent for the removal of VOCs.