Functionalized biochar for the removal of poly- and perfluoroalkyl substances in aqueous media

Biochar has gained attention as a promising adsorbent for removing various environmental pollutants due to its availability, cost-effectiveness, eco-friendly nature, and high adsorption capacity. This review focuses on using biochar to remove poly- and perfluoroalkyl substances (PFAS), emerging contaminants that pose significant environmental and health risks due to their toxicity, persistence, and bioaccumulation potential. The classification of biochar and using pristine and functionalized biochar for pollutant removal are addressed, along with an overview of the various functionalization techniques employed to enhance biochar's adsorption capacity. Different factors influencing the removal of poly- and perfluoroalkyl substances (PFAS), such as pH, the molecular chain length of PFAS, and biochar characteristics like pyrolysis temperature, particle size, and dosage, are investigated. Long-chain PFAS, such as perfluoro octane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are more effectively adsorbed than short-chain PFAS, with competitive sorption effects observed in mixed-solution environments. A decrease in pH, smaller biochar particle sizes, and optimized pyrolysis temperatures have been found to enhance biochar's sorption capacity. Furthermore, biochar demonstrates higher efficiency in single-solution systems compared to mixed solutions when removing PFAS.