A novel gallic acid modification and high-temperature alkali activation mesoporous biochar enables ultrafast and high-capacity removal of short- and long-chain PFAS from water

Biochar is increasingly recognized as a promising remediation material for per- and polyfluoroalkyl substances (PFAS), yet its practical application is limited by modest adsorption capacities and insufficient mechanistic understanding. Herein, nine types of biochars were systematically screened, leading to the development of a gallic acid (GA) modification and high-temperature (850 °C) potassium hydroxide (KOH) activation corncob biochar (GKCC850). The resulting mesoporous biochar GKCC850 exhibits an exceptionally high specific surface area (SSA) (2782.8 m²/g), large mesopore volume (1.423 cm³/g), enhanced hydrophilicity (contact angle (CA) = 56.63°), and abundant oxygen-containing functional groups. GKCC850 delivers outstanding adsorption performance toward PFAS of varying chain lengths, achieving experiment uptake capacities of 1170.10 mg/g for perfluorooctanoic acid (PFOA) and 349.25 mg/g for perfluorobutanoic acid (PFBA)—increases of 136.1% and 91.5% relative to pristine biochar—with adsorption equilibrium reached within 60 min. Alkaline conditions and dissolved organic matter were identified as key inhibitory factors. Combined experimental evidence and density functional theory (DFT) calculations reveal that GKCC850 enhances PFAS removal through synergistic mesopore filling, electrostatic attraction, hydrophobic interactions, and surface complexation. High relative adsorption capacity (> 75%) after five regeneration cycles and minimal reductions in adsorption coefficient (logK_d) (0.15–0.45 units) in river water and wastewater influent confirm the material's structural stability and practical applicability. Overall, this study establishes GA modification and high- temperature alkali activation as an effective strategy for engineering high- performance biochars and provides mechanistic insights for designing next-generation PFAS adsorbents.