Microwave-assisted activated carbon from waste compressed wood for efficient PFOS removal under neutral pH conditions

Perfluorooctanesulfonic acid (PFOS) is a persistent fluorinated contaminant that presents serious challenges for water treatment due to its chemical stability and mobility. In this study, a sustainable activated carbon was synthesized from discarded compressed wood through phosphoric acid impregnation followed by microwave assisted activation. Response surface methodology was applied to optimize both the synthesis conditions and the adsorption process. The optimized synthesis produced an adsorbent with a high specific surface area of 1226 m² g⁻¹, well developed mesoporosity, and abundant oxygen and phosphorus containing surface functionalities. Adsorption optimization identified a contact time of 4.82 h, adsorbent dosage of 1.95 g L⁻¹, and natural solution pH of 7.0 as the optimal operating conditions, achieving a PFOS removal efficiency of 97.87 percent at an initial PFOS concentration of 5 mg L⁻¹. Adsorption equilibrium was best described by the nonlinear Langmuir isotherm with a maximum adsorption capacity of 60.85 mg g⁻¹, while adsorption kinetics followed a pseudo second order model, indicating surface controlled interactions. The adsorbent also exhibited excellent regeneration performance, maintaining more than 95 percent of its removal efficiency after multiple reuse cycles. The combination of waste derived precursor utilization, rapid microwave assisted synthesis, high removal efficiency under neutral pH conditions, and strong reusability highlights the potential of this material as a practical and scalable adsorbent for PFOS remediation in water and wastewater treatment systems.