Efficient adsorption of perfluorooctanoic acid by aminosilanized biochar: Optimization, mechanism, and performance in real dyeing effluent

The pervasive contamination of aquatic environments by per - and polyfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA), poses a critical challenge to global water security due to their recalcitrance and bioaccumulation. To address this, a high-performance, sustainable adsorbent (AC-HCl-NH 2 ) was developed by grafting 3-aminopropyltriethoxysilane (APTES) onto bamboo-derived activated biochar to fabricate a hierarchical amino-functionalized composite. The modified biochar exhibited outstanding adsorption performance for PFOA, achieving a maximum adsorption capacity of 163.7 mg/g. The key parameters for the APTES-mediated modification process (68.75 °C, reaction duration of 9.07 h, and APTES dosage of 0.32 g/g) were optimized through a response surface methodology (RSM) approach. Density functional theory (DFT) calculations elucidated that electrostatic attraction between protonated surface amino groups and PFOA anions is the dominant driving force. Furthermore, adsorption energy calculations confirmed a significant energetic advantage for the configuration where polar end groups are oriented toward the surface (−1.16 eV vs. -0.42 eV). Notably, in treating real dyeing wastewater containing an initial PFOA concentration of 250 ng/L, AC-HCl-NH 2 achieved a removal efficiency of 75.5%, reducing the residual concentration to approximately 61.3 ng/L. This result holds significant engineering implications, as the residual concentration successfully meets the limit of 80 ng/L mandated by Chinese Standards for Drinking Water Quality (GB 5749–2022), a benchmark unattainable by unmodified biochar. Collectively, this study validates the material's robust interference resistance in complex matrices and presents a cost-effective engineering solution for complying with increasingly stringent PFAS regulations.