Enhanced adsorption of aromatic VOCs on hydrophobic porous biochar produced via microwave rapid pyrolysis

To customize biochar suitable for efficient adsorption of benzene derivatives, this study presents programmed microwave pyrolysis to produce hydrophobic porous biochar with low-dose ferric chloride. Designated control of the ramping rates in the carbonization stage and the temperatures in the activation stage were conducive to enlarging the specific surface area. Iron species, including amorphous iron minerals, could create small-scale hotspots during microwave pyrolysis to promote microporous structure development. Compared with conventional pyrolysis, programmed microwave pyrolysis could increase the specific surface area from 288.6 m² g⁻¹ to 455.9 m² g⁻¹ with a short heating time (15 min vs. 2 h) under 650 °C. Engineered biochar exhibited higher adsorption capacity for benzene and toluene (136.6 and 94.6 mg g⁻¹), and lower adsorption capacity for water vapour (6.2 mg g⁻¹). These findings provide an innovative design of engineered biochar for the adsorption of volatile organic compounds in the environment.