Adsorption of hydroxychloroquine and paracetamol on H3PO4-activated carbon from coconut husk: Single - and two-component adsorption systems

In this study, the adsorption of hydroxychloroquine (HQC) and paracetamol (PCT) from single and two-component systems were investigated using activated carbon (AC) produced from coconut husk and H 3 PO 4 (1:1 v/w) under slow pyrolysis conditions. The material was comprehensively characterized by physicochemical and textural analyses and exhibited high yield (38.88%), well-developed porous structure, high BET surface area (S BET = 1311 m 2 g −1 ), and significant mesoporous fraction. The AC also showed good thermal stability and predominantly acidic surface functionalities, as indicated by pH PZC of 3.0. In single-component systems, adsorption performance was strongly dependent on solution pH, with higher removal efficiencies observed under acidic and neutral conditions. Kinetic data were best described by pseudo-second-order and Elovich models, suggesting chemisorption contributions, while intraparticle diffusion analysis indicated greater diffusion of PCT, consistent with its higher Knudsen diffusivity (DK) values. Equilibrium studies demonstrated that the Langmuir model best fitted the PCT-AC system, whereas the Freundlich model more adequately represented HQC-AC behavior, with maximum adsorption capacities of 272 mg g −1 for PCT and 198 mg g −1 for HQC. In two component systems, adsorption capacities decreased (PCT = 200–168 mg g −1 ; HQC = 127–108 mg g −1 ), confirming competitive interactions between adsorbates. The Sheindorf-Rebuhn-Sheintuch (SRS) and extended Freundlich models provided the best fits for multicomponent equilibrium data. SRS parameters indicated stronger affinity of AC for PCT, with selectivity constants (a ij ) of 5.11 for PCT and 1.72 for HQC, confirming competitive inhibition of HQC adsorption by PCT molecules.