Alkali-Modified Biochar Derived from Waste Bamboo Powder for the Effective Adsorption of Perfluorooctanoic Acid

Bamboo powder waste generated from bamboo processing serves as an ideal feedstock for biochar (BC). This study employed potassium hydroxide (KOH) to modify biochar derived from bamboo powder waste, activating it at different temperatures (700 °C, 800 °C, and 900 °C) to yield samples designated KBC-700, KBC-800, and KBC-900, respectively. The physicochemical properties and pore structures of the modified biochar were characterized using SEM, specific surface area and pore size analysis, FT-IR, Raman spectroscopy, XRD, and zeta potential measurements. The adsorption performance of the modified biochar toward PFOA was investigated using kinetic and thermodynamic models, examining the effects of the solution pH, adsorbent dosage, and temperature. Results indicate that KBC-900 exhibits a significantly enhanced specific surface area (up to 2924.7 m2 g−1), reduced surface oxygen-containing functional groups, increased carbon skeleton aromatization, and expanded mesoporous channels. Under initial conditions of pH = 3 and reaction temperature of 298 K, KBC-900 achieved a PFOA adsorption capacity of 366.7 mg g−1 with a removal efficiency of 91.67%. The adsorption process conformed to pseudo-first-order and pseudo-second-order kinetic models as well as the Freundlich model. The adsorption equilibrium was reached within 12 h, indicating multi-layer adsorption dominated by chemisorption on a heterogeneous surface. Thermodynamic parameters indicate the adsorption reaction is an exothermic process. After five cycles of regeneration, KBC-900 maintained a removal efficiency of 75.69%. This study provides an efficient and reliable solution for removing PFOA from water.