Magnetic chitosan kaolinite cellulose nanofibril cryogel beads for efficient removal of methylene blue from water

Using a green freeze gelation and genipin crosslinking technique, chitosan (C), kaolinite (K), cellulose nanofibrils (CNF), and Fe₃O₄ nanoparticles were combined to create CK-CNF-Fe cryogel beads, a novel magnetic composite. Freeze gelation was used to create the beads, which were then cross linked using genipin, a non-toxic natural cross linker, and Fe₃O₄ nanoparticles were included in situ. The addition of genipin guarantees the material's safe application in wastewater treatment while also enhancing its eco-friendliness. With an average pore width of about 11 μm, an average bead diameter of 1.7 mm, and a specific surface area of 230 m² g⁻¹, the beads displayed a macroporous three dimensional structure. The maximum adsorption capacity was 812 mg g⁻¹ at pH 7 and 298 K in batch adsorption studies using Methylene Blue (MB, 150 mg L⁻¹), which fit the Langmuir isotherm model (R² > 0.995). 95% equilibrium absorption was reached in 22 min, and adsorption proceeded according to pseudo second order kinetics (k₂ = 0.016 g mg⁻¹ min⁻¹). Using a 0.3 T magnet, the beads' great magnetic responsiveness (saturation magnetization, Mₛ = 20 emu g⁻¹) allowed for > 99% recovery in less than 35 s. >90% dye desorption during regeneration at pH 2 was made possible by the pH-responsive swelling behavior, which ranged from 500% (pH 3) to 880% (pH 10). Surprisingly, after six adsorption desorption cycles, the beads retained more than 90% of their adsorption effectiveness. These results highlight CK-CNF-Fe cryogel beads as eco-friendly, high performance, and magnetically retrievable adsorbents with excellent reusability for sustainable wastewater treatment.