Highly selective and reusable nanoadsorbent based on FeO-embedded sodium alginate-based hydrogel for cationic dye adsorption: Adsorption interpretation using multiscale modeling.

This study aims to develop a stable and efficient magnetic nanocomposite hydrogel (MNCH) for selective removal of methylene blue (MB) and crystal violet (CV). MNCHs with different FeO contents (0-9 wt%) were synthesized following graft co-polymerization method using sodium alginate, acrylamide, itaconic acid, ammonium persulfate and N,N-methylene bisacrylamide. Among them, MNCH, with 5 wt% FeO, showed highest removal efficiency (>95 %). Optimal dye removal occurred at pH 10, with 40 min for CV and 60 min for MB using 30 mg dose. MNCH was characterized using various techniques, with X-ray diffraction (XRD) revealing crystallite size of 30.5 nm, and Brunauer-Emmett-Teller (BET) indicating surface area of 59.80 m g. Adsorption kinetics followed fractal pseudo-first-order and fractal Vermeulen diffusion models, reflecting MNCH's heterogeneous nature as suggested by fractal exponent (h) ranging 0.38-0.44, significantly deviating from zero. Langmuir-Freundlich isotherm accurately described the process, demonstrating MNCH's superior affinity for MB (4216.69 mg g) over CV (3730.17 mg g). Thermodynamics of MB adsorption was exothermic as suggested by negative ΔH value, while CV adsorption was endothermic. Density functional theory confirmed stronger interaction between MNCH and MB (E = -49.29 kcal mol) compared to CV (E = -41.30 kcal mol). These findings underscore MNCH's excellent adsorption capacity, making it promising for removing dyes.