Zero Valent Iron Impregnated Sodium Alginate Grafted (Acrylamide-Co-Acrylic Acid) Adsorbents for the Removal of Methylene Blue in Aqueous Systems

In this study sodium alginate (NaAlg) grafted acrylamide (AM)-co-acrylic acid (AA)) and nano zero-valent iron (nZVI) were synthesized by the microwave assisted and coprecipitation method, respectively. The nZVI was dispersed in NaAlg-g-(AM-co-AA) and the adsorbent was characterized by X-ray diffraction (XRD), proton nuclear magnetic resonance ((HNMR)-H-1), and Fourier transform infrared spectroscopy (FTIR). In order to evaluate the effects of adsorbent dosage, contact time, pH, initial dye concentration and temperature, kinetic and thermodynamic tests were carried out on the adsorbents. The best dose of the NaAlg-g-(AM-co-AA)/nZVI with 0.5% nZVI needed to remove methylene blue (MB) dye (10 mg/L, 50 mL) was 0.2 g at 60 min. For NaAlg-g-(AM-co-AA)/nZVI to effectively remove a large portion of MB dye, pH 8.0 was ideal. To assess the adsorption data, Freundlich, Langmuir, and Dubinin-Radushkevich isotherm models were applied. The Langmuir isotherm performed best for MB adsorption, with an R-2 of 0.975. The adsorption equilibrium's kinetic process followed the pseudo-second-order model (R-2=0.9988). The positive Delta G(o) values obtained from the thermodynamic studies showed that the adsorption processes were endothermic and non-spontaneous.