title: Aqueous Aggregation Behavior of Engineered Superparamagnetic Iron Oxide Nanoparticles: Effects of Oxidative Surface Aging.
abstract: For successful aqueous-based applications, it is necessary to fundamentally understand and control nanoparticle dispersivity and stability over a range of dynamic conditions, including variable ionic strengths/types, redox chemistries, and surface ligand reactivity/degradation states (i.e., surface aging). Here, we quantitatively describe the behavior of artificially aged, oleic acid (OA) bilayer coated iron oxide nanoparticles (IONPs) under different scenarios. Hydrogen peroxide (H2O2), used here as a model oxidant under both dark and light ultraviolet (UVA) conditions, was employed to "age" materials, to varying degrees, without increasing ionic strength. Short-term stability experiments indicate that OA-IONPs, while stable in the dark, are effectively destabilized when exposed to UVA/H2O2/•OH based oxidation processes. Compared to bicarbonate, phosphate (1.0 mM) has a net stabilizing effect on OA-IONPs under oxidative conditions, which can be attributed to (surface-based) functional adsorption. Corresponding aggregation kinetics in the presence of monovalent (Na+) and divalent cations (Ca2+) show that attachment efficiencies (α) are strongly dependent on the cation concentrations/types and degree of surface aging. Taken together, our findings directly highlight the need to understand the critical role of particle surface transformation(s), via oxidative aging, among other routes, with regard to the ultimate stability and environmental fate of surface functionalized engineered nanoparticles.
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Wenlu
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Seung Soo
authors.initials: SS
authors.lastname: Lee
authors.affiliation: Department of Civil and Environmental Engineering, Tufts University , Medford, Massachusetts 02155, United States.
authors.forename: Anjuliee M
authors.initials: AM
authors.lastname: Mittelman
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Di
authors.initials: D
authors.lastname: Liu
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Jiewei
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Carl H
authors.initials: CH
authors.lastname: Hinton
authors.affiliation: Department of Civil and Environmental Engineering, Tufts University , Medford, Massachusetts 02155, United States.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Abriola
authors.affiliation: Department of Civil and Environmental Engineering, Tufts University , Medford, Massachusetts 02155, United States.
authors.forename: Kurt D
authors.initials: KD
authors.lastname: Pennell
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: John D
authors.initials: JD
authors.lastname: Fortner
mesh_terms: D006861:Hydrogen Peroxide; D058185:Magnetite Nanoparticles; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D013499:Surface Properties; D014867:Water
chemical_list: D058185:Magnetite Nanoparticles; D014867:Water; D006861:Hydrogen Peroxide