Design of an Advanced Biochar Material for Removing Short-Chain PFAS from Water

Short-chain per- and polyfluoroalkyl substances (PFAS) have emerged as a challenging issue in water remediation due to their strong hydrophilicity and small molecular dynamic dimensions. Most current studies on biochar-based PFAS removal treat short-chain PFAS as secondary issues related to long-chain congeners. These technologies often apply classical theoretical frameworks, including hydrophobic interactions, electrostatic attraction, and conventional micropore filling, to explain mechanisms and develop functional materials. However, recent experimental evidence suggests that the dominant adsorption behavior of short-chain PFAS at biochar interfaces differs substantially from that of long-chain PFAS. First, the key capture process for short-chain PFAS appears to occur within sub-nanoporous domains with sizes between 0.56 and 0.85 nm, rather than within the broad microporous structures traditionally assumed. In addition, design principles based on synergistic pore–surface chemistry for long-chain PFAS may cause irreversible damage to sub-nanopores through metal-loading modifications, potentially reducing short-chain PFAS adsorption performance. Finally, material regeneration and disposal strategies for short-chain PFAS may need to shift from passive physical adsorption toward integrated adsorption–degradation systems. The main contribution of this perspective is to propose an independent mechanistic and material design framework for short-chain PFAS removal, based on the possible synergy between sub-nanopores and surface basic sites, and to outline a transition from passive adsorption to integrated adsorption–degradation. Future breakthroughs may depend less on pursuing ultra-high adsorption capacities alone and more on the precise, synergistic control of pore structure and surface chemistry, enabling combined adsorptive enrichment and in situ degradation.