Dual-purpose magnetic κ-carrageenan/montmorillonite hydrogel for carrying and removal of tetracycline from aqueous medium

In this work, a novel magnetic adsorbent obtained via the conjugation of montmorillonite clay and κ-carrageenan was fabricated. The successful synthesis of adsorbent was confirmed by various analytical techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, zeta potential measurements, scanning electron microscopy, and N₂-adsorption/desorption isotherms. The synthesized material was used as a high-performance sorbent in the removal of tetracycline from aqueous media, and the influential parameters of the process were investigated. It showed high adsorption performance in a wide pH range of 4–11. A maximum adsorption capacity of 80.28 mg g⁻¹ was obtained at 45 °C. Furthermore, the best-fitted kinetic model was found to be the pseudo-second-order model. Regarding two-parameter nonlinear isotherms, best fitting followed the order: Freundlich ≈ Redlich-Peterson > Temkin > Langmuir, which was not the same that was obtained using linear isotherm model regression (Langmuir ≈ Redlich-Peterson > Temkin > Freundlich). Among the different isotherm models, the isotherm data was best fitted to the nonlinear Sips isotherm model. Thermodynamic studies showed the endothermic and spontaneous nature of the adsorption process, as well as its random motion. A plausible mechanism includes hydrogen bonds as well as electrostatic and anion-π interactions as adsorption interactions between tetracycline and the functional groups (O-SO₃^- and OH^–) on the surface of magnetic clay/biopolymer adsorbent.