Effects of fulvic acid on aggregation, sedimentation, and adsorption of FeO magnetic nanoparticles.

Environmental behavior, bioavailability, and risks posed by FeO, magnetic nanoparticles (FeO NPs) in surface waters are affected by complex geochemistry, including pH and inorganic and organic matter. This work provides a systematic analysis of adsorption of fulvic acid (FA) on surfaces of FeO NPs with adsorption kinetics, adsorption thermodynamic, and adsorption isotherm. Adsorption of FA on surfaces of FeO NPs is consistent with assumptions of Langmuir and Freundlich adsorption isotherm models. The adsorption amount of FA was inversely proportional to solution pH, and the maximum amount is 128.6 mg g. Adsorption of FA on surfaces of FeO NPs is a spontaneous endothermic process. FA plays an important role in aggregation and suspension/sedimentation behavior of FeO NPs in aquatic environmental. With continuous adsorption of FA, electrostatic repulsion between the particles and the steric hindrance of FA significantly decreased aggregation and increased suspension of FeO NPs. The results of FTIR and XPS indicated that FA was adsorbed on FeO NPs mainly through chemical reactions, and carbohydrates particularly play an important role in adsorption.