A magnetic bio-based adsorbent prepared from Fe ₃ O ₄ nanoparticles impregnated with diatom frustules and sodium alginate for methylene blue uptake: advanced modeling and mechanism

Abstract

Herein, magnetic iron oxide nanoparticles (MNPs) were impregnated with diatom frustules (DF) and sodium alginate (SA) to fabricate a magnetic bio-based adsorbent for the removal of methylene blue (MB) dye. The developed MNPs@DF/SA was characterized by XRD, TGA, DSC, FTIR, FESEM-EDX, TEM, and zeta potential techniques. Methylene blue (MB) adsorption was theoretically assessed at solution pH 8.0, adsorbent mass (50 mg), shaking time (4 h), MB concentration (100–400 mg/L), and different temperatures of 25, 40, and 50°C. A multilayer statistical model was the best in fitting the MB adsorption experiments at all solution temperatures. The number of MB molecules at each functional group (the steric n parameter) was between 1.16–1.33, which suggesting vertical geometry and multi-molecular mechanism. The adsorption capacity at saturation (Qsat) increased from 647.42 to 779.45 mg/g with increasing temperature from 25 to 50°C signifying an endothermic adsorption system. Extending the adsorption energies from 31.90 to 37.47 kJ/mol indicated that the MNPs@DF/SA – MB interactions were controlled by physical forces as electrostatic interactions. The fabricated MNPs@DF/SA reserved more than 79% of MB capture after five regeneration cycles, which recommended the suitability of this adsorbent in the removal of MB at an industrial level.