A comparative study of the removal of methylene blue by iron nanoparticles from water and water-ethanol solutions

Nano-zero valent iron (nZVI) was synthesized and used for the removal of methylene blue (MB) dye from water and water-ethanol solutions. The experiments investigated the effects of time, concentration, nZVI dose, and temperature. MB was removed almost totally from water solutions, while limited removal was achieved in water-ethanol solutions. In both cases, MB removal was fast. The loading data was fitted to a linear isotherm, and phenomenological equilibrium constants (K) of the sorption process were determined. The K values in water medium were much above those in water-ethanol mixtures, and ranged from 18,084-36,080 depending on the operating conditions. The MB removal process was more endothermic, and generated more system entropy in water-ethanol media, with Delta H degrees and Delta S degrees values ranging from 7.5-38.2 kJ/mol and 77.9-179.5 J/mol.K, respectively. A Fenton-like oxidation process of MB resulted in smaller MB removal from water-ethanol solutions compared with water solutions under the studied conditions. (C) 2018 Elsevier B.V. All rights reserved.