Adsorption of perfluorooctane sulfonate (PFOS) on corn straw-derived biochar prepared at different pyrolytic temperatures

The adsorption behavior of perfluorooctane sulfonate (PFOS) on biochar produced from corn straw at varying pyrolytic temperatures (i.e., 250, 400, 550, and 700°C, BC250–700, respectively) was investigated. High pyrolytic temperatures (>400°C) resulted in the increase of some fine-pore structures, larger surface area (SA) and higher aromaticity of biochar. The adsorption kinetics of PFOS fitted well to a pseudo-second order model while the adsorption isotherms followed a Langmuir adsorption isotherm model (R2 > 0.949). The adsorption capacity increased with the pyrolytic temperature with the highest adsorption capacity (i.e., 169.30 mg/g) being obtained on BC 700. The adsorption of PFOS on the biochar samples was mainly governed by hydrophobic and electrostatic interactions. The hydrophobicity enhancement of biochar pyrolyzed at high temperatures is one of the important factors contributing to PFOS adsorption. The capacity of biochar for adsorbing PFOS decreased with the increase of solution pH. The adsorption of PFOS on the biochar samples is a spontaneous and endothermic process.