Biomass-derived activated carbon from Scolymus hispanicus: activation strategy and adsorption mechanism of hydroxychloroquine

Abstract

Biosorption offers a sustainable approach for the removal of pharmaceutical contaminants from wastewater. This study reports, for the first time, the use of activated carbon derived from Scolymus hispanicus biomass as a low-cost, eco-friendly adsorbent for the removal of hydroxychloroquine sulfate (HCQ) from aqueous solutions. Adsorption performance was evaluated through equilibrium and kinetic studies, with data analyzed using Langmuir and Freundlich isotherm models, a pseudo-second-order kinetic model, and intraparticle diffusion analysis to elucidate the underlying adsorption mechanism. The biosorbent exhibited a maximum adsorption capacity of 23.17 mg g⁻¹ under the investigated conditions. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were independently determined, revealing that the adsorption process is spontaneous and endothermic, as inferred from negative ΔG° and positive ΔH° values, rather than from adsorption capacity alone. The integrated analysis of isotherm, kinetic, and thermodynamic results provides a comprehensive mechanistic interpretation. This work highlights the novelty of using Scolymus hispanicus as a sustainable precursor and demonstrates its potential as a cost-effective and environmentally friendly alternative to conventional activated carbons for pharmaceutical wastewater treatment.