Enhanced adsorption of benzo(a)pyrene in soil by porous biochar: Adsorption kinetics, thermodynamics, and mechanisms

Soil pollution caused by polycyclic aromatic hydrocarbons (PAHs) poses a significant threat to human health and ecosystems. In this study, a novel porous biochar (PBC) was fabricated from biowastes by one-pot pyrolysis using potassium hydrogen carbonate (KHCO3) as a porogen. The as-prepared PBC was used to remove benzo(a)pyrene (BaP) in contaminated soil for the first time. The PBC obtained at 900 °C had a large surface area (2017.59 m2 g–1), which was approximately 165 times that of the original biochar (BC) (12.16 m2 g–1). The maximum adsorption capacity of BaP by the PBC reached 29.82 mg g–1, which was significantly higher than that of BC (6.94 mg g–1). Adsorption kinetics study indicated the adsorption process fitted a pseudo-second order model, and the adsorption isotherms were consistent with Langmuir model, suggesting BaP adsorption was probably a monolayer molecular adsorption process and that chemisorption was involved. Batch experiments showed that the adsorption efficiency remained high under different initial BaP concentration, initial pH values, temperature, inorganic anion, and humic acid conditions. The results suggested that pore-filling and π-π electron donor-acceptor (EDA) interactions were the main mechanisms for BaP adsorption by PBC, whereas hydrogen bonding and electrostatic interactions only partially contributed to the adsorption process. The soil leaching experiments suggested that the addition of PBC effectively reduced BaP leaching after soil remediation. This study not only provided a cost-effective biochar adsorbent for BaP-contaminated soil remediation, but also shed lights on the mechanisms about adsorption of BaP by PBC in soil.