KOH-activated biochar derived from Pinus brutia wildfire residues for efficient sulfamethoxazole removal: adsorption mechanisms and process optimization.

Sulfamethoxazole (SMX) is a persistent antibiotic frequently detected in aquatic environments, posing significant risks to ecosystem health and promoting antibiotic resistance. In this study, a highly porous KOH-activated biochar (KA-BC-WFR) was synthesized from wildfire residues of Pinus brutia and applied for the efficient removal of SMX from aqueous solutions. Textural characterization revealed a highly developed hierarchical pore structure; N2 adsorption-desorption isotherms determined a high BET specific surface area of 828 m2 g-1 with an average pore diameter of 1.30 nm, confirming a predominantly microporous structure, while Scanning Electron Microscopy (SEM) displayed a sponge-like morphology with macroporous transport channels ranging from 1.0 to 9.6 µm. The point of zero charge (pHPZC) of the biochar was determined to be 6.24 using the pH drift method. Response Surface Methodology (RSM) optimized the process, identifying pH 2.0 as the optimal condition. Kinetic studies followed the pseudo-second order model, and equilibrium data were best fitted by the Redlich-Peterson and Toth models. The maximum monolayer adsorption capacity (q max) was 160.05 mg g-1 at 298 K. Thermodynamic parameters confirmed that the process was spontaneous (ΔG° < 0) and exothermic (ΔH° = -11.93 kJ mol-1). The adsorption mechanism was attributed to a synergistic effect of rapid pore filling, strong hydrogen bonding between the neutral SMX species and surface functional groups, and π-π stacking interactions. These findings demonstrate that converting wildfire residues into activated biochar is a highly effective strategy for pharmaceutical wastewater remediation.