High-capacity adsorption of fluoxetine using olive-stone derived activated biochar: insights into efficiency and mechanism

The increasing incidences of mood, anxiety, and panic disorders have made fluoxetine (FLX), known for its safety and therapeutic efficiency, one of the most widely prescribed antidepressants globally. However, due to its resistance to natural photolysis and hydrolysis, coupled with the potential to cause endocrine disruption, FLX has become an emerging contaminant, requiring urgent attention for removal. In this context, the present study explores the specific application and integration of physically activated biochar derived from olive stone-an agro-industrial waste-for the targeted removal of FLX. By optimizing activation parameters (CO₂-1000-30-600-1), this study demonstrates the ability to achieve superior adsorption capacities for FLX, which surpass the adsorption capacity of previously reported waste-derived biochar used for FLX removal. The maximum adsorption capacity for the biochar ranged from 4.82 ± 0.04 to 146.45 ± 10.55 mg g^-1 for initial FLX concentrations of 1 to 50 mg L^-1, respectively, for a biochar dose of 0.2 g L^-1. Furthermore, the adsorption kinetics data revealed that the biochar-FLX interaction followed the Langmuir adsorption isotherm and a pseudo-second-order kinetic model, indicating irreversible adsorption of FLX onto the homogenous surface of the biochar. Non-electrostatic and non-hydrophobic interactions, such as hydrogen bonding, pore filling, and π-π EDA forces, were identified as the primary interactions facilitating FLX adsorption onto the biochar. This study, therefore, presents a novel approach addressing the dual objectives of environmental remediation and zero-waste principles, contributing significantly to advancing sustainable solutions for emerging contaminants.