Environmental behavior of per- and polyfluoroalkyl substances (PFASs) and the potential role of biochar for its remediation: a review

Per- and polyfluoroalkyl substances (PFASs), commonly known as ''forever chemicals'', are persistent organic pollutants that are widely distributed in the environment. Due to their toxicity and resistance to degradation, PFASs are classified as emerging contaminants, and increasing attention is being paid to their remediation. Biochar, an environmentally friendly and cost-effective adsorbent, shows potential for remediating PFASs contamination. The application of biochar for PFASs remediation has garnered growing interest. Compared to other adsorbents, biochar is more economical and the raw materials for its preparation are more readily available. However, there is currently no comprehensive review summarizing the effects of biochar on the environmental behavior of PFASs. This review aims to fill that gap by providing an in-depth discussion and synthesis of the existing literature in this area. It focuses on the environmental behavior of PFASs, specifically addressing the adsorption mechanisms and factors influencing the effectiveness of biochar in PFASs remediation. A proposed mechanism by which biochar photodegrades PFASs through the generation of free radicals, in addition to conventional adsorption mechanisms (such as pore filling, hydrogen bonding, hydrophobic interactions, and electrostatic interactions), is explored. Furthermore, this review discusses the ability of biochar to reduce the likelihood of PFASs entering the food chain through water and soil and evaluates the feasibility and limitations of using biochar for PFASs removal. Finally, we identify future research directions to support the safe and effective use of biochar for PFASs remediation, so as to promote the advancement of green remediation technologies.