Synergistic engineering of bio-inspired magnetic alginate-chitosan interpenetrating double-network beads for rapid simultaneous capture of arsenic and phosphate from complex water systems.

The increasing pollution of water aquatic systems by the oxyanionic metalloids and nutrients requires the design of multipurpose, readily arrestable adsorbents. The research problem addressed in this study was to study the synergistic production of magnetically responsive alginate-chitosan-Fe3O4 (ACF) nanocomposites that can operate in the simultaneous removal of pentavalent arsenic [As(v)] and orthophosphate [PO4 3-] in complex aqueous matrices. ACF nanocomposite was prepared using an in situ mineralized co-precipitation of ferric and ferrous salts in a biopolymeric template, which was then, cross-linked droplet wise with calcium chloride and glutaraldehyde ions. FTIR, SEM, TEM, EDX, BET, TGA, DSC, and XPS were important in characterizing the structural of prepared nanocomposites. TEM analysis showed spherical nanoparticles with a diameter of 45 nm on average and anchored in a porous carbohydrate matrix. Vibrating Sample Magnetometry showed that the saturation magnetization was 26.1 emu g-1 with negligible coercivity and remanence, confirming superparamagnetic behavior at room temperature. This high magnetization enabled rapid magnetic separation of the ACF nanocomposite from aqueous suspension within 30 seconds using an external neodymium magnet (0.5 T), as determined by time-resolved turbidity and ICP-OES measurements. The experiment of batch adsorption established the maximum Langmuir adsorption capacity of As(v) and orthophosphate 114.5 mg g-1 and 138.2 mg g-1 at pH 6.5, respectively with initial pollutant ions concentration 50 mg L-1, ACF 1.0 g L-1, after 240 min. Kinetic modeling was done along pseudo-second-order mechanism implying chemisorption through inner-sphere complexation. The shifting in FTIR bands and appears new Fe-O-As/P bonds confirm key adsorption mechanisms. The nano-architectures were highly reusable with >90% of their original capacity remaining after five cycles and >85% after six cycles of regeneration. This study offers a solid guideline in the creation of bionanocomposites that may counter multi-pollutants in the design of a decentralized water treatment plant.