Cross-linked alginate/pozzolan (Alg@PZ) microcapsules for sodium diclofenac removal as emerging contaminant

This study investigates the adsorption of sodium diclofenac (SDF) onto Alginate/Pozzolan (Alg@PZ) microcapsules to address pharmaceutical contamination in aquatic systems. The Alg@PZ composite was synthesised via CaCl₂ cross-linking by varying the Sodium Alginate (S-Alg)/Pozzolan (PZ) mass ratio from 0.625 to 3.25. Successful PZ incorporation into the S-Alg matrix was confirmed by FTIR, XRD and SEM analyses, revealing hydrogen and electrostatic bonding alongside a near-uniform spherical porous morphology of 1.73 mm diameter. TGA revealed optimal PZ encapsulation of 63.87% at a S-Alg/PZ ratio of 0.625, with high thermal stability. Adsorption experiments in a shallow-bed system demonstrated rapid SDF removal, best described by a PSO kinetic model reaching equilibrium after 45 minutes, with a q_max= 21.85 mg.g ^{- 1}. Thermodynamic analysis showed that the reaction was spontaneous and exothermic. However, Alg@PZ_0.625 represents a scalable, eco-friendly and cost-effective alternative to conventional adsorbents for removing persistent pharmaceutical compounds from aqueous systems.