Magnetic polypyrrole-alginate microspheres derived from biogenic CaCO3 from oyster shells for bisphenol A removal in aqueous environment: Kinetics and thermodynamic study.

Adsorption is a widely used remediation technique for the removal of bisphenol A (BPA) in water, yet many adsorbents exhibit limited adsorption capacity and poor reusability. To address these limitations, this study synthesized a low-cost and green porous magnetic polypyrrole@Fe₃O₄@alginate adsorbent (magnetic strength of 2.658 emu/g), utilizing sacrificial CaCO₃ derived from waste oyster shells. The magnetic adsorbent was comprehensively characterized using FTIR, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, and Brunauer-Emmett-Teller analysis, confirming its structural and morphological integrity. Adsorption performance was investigated using spectrofluorimetric analysis under optimized conditions (5 mg/L BPA, pH 3, 25 °C, 50 min contact time, and 20 mg adsorbent dosage), provided a maximum adsorption capacity of 87.23 mg/g at 25 °C. Kinetic studies demonstrated that the adsorption process followed Elovich kinetic model with R² = 0.9993 and the lowest χ² = 2.6746, while equilibrium data were best described by the Redlich-Peterson isotherm model with the highest R² = 0.9977 and the lowest χ² = 2.6746. Notably, the adsorbent demonstrated good adsorption efficiency, and relatively good reusability (removal efficiency of 41.5 % efficiency after five cycles), highlighting its potential for removing BPA removal from aqueous environments.