title: Formation of iron(III) (hydr)oxides on polyaspartate- and alginate-coated substrates: effects of coating hydrophilicity and functional group.
abstract: To better understand the transport of contaminants in aqueous environments, we need more accurate information about heterogeneous and homogeneous nucleation of iron(III) hydroxide nanoparticles in the presence of organics. We combined synchrotron-based grazing incidence small-angle X-ray scattering (GISAXS) and SAXS and other nanoparticle and substrate surface characterization techniques to observe iron(III) (hydr)oxide [10⁻⁴ M Fe(NO₃)₃ in 10 mM NaNO₃] precipitation on quartz and on polyaspartate- and alginate-coated glass substrates and in solution (pH = 3.7 ± 0.2). Polyaspartate was determined to be the most negatively charged substrate and quartz the least; however, after 2 h, total nanoparticle volume calculations--from GISAXS--indicate that positively charged precipitation on quartz is twice that of alginate and 10 times higher than on polyaspartate, implying that electrostatics do not govern iron(III) (hydr)oxide nucleation. On the basis of contact angle measurements and surface characterization, we concluded that the degree of hydrophilicity may control heterogeneous nucleation on quartz and organic-coated substrates. The arrangement of functional groups at the substrate surface (--OH and --COOH) may also contribute. These results provide new information for elucidating the effects of polymeric organic substrate coatings on the size, volume, and location of nucleating iron hydroxides, which will help predict nanoparticle interactions in natural and engineered systems.
authors.affiliation: Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, USA.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Ray
authors.forename: Byeongdu
authors.initials: B
authors.lastname: Lee
authors.forename: Jonas
authors.initials: J
authors.lastname: Baltrusaitis
authors.forename: Young-Shin
authors.initials: YS
authors.lastname: Jun
mesh_terms: D000464:Alginates / Q000737:chemistry*; D004777:Environment; D005290:Ferric Compounds / Q000737:chemistry*; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D018625:Microscopy, Atomic Force; D053758:Nanoparticles / Q000737:chemistry / Q000648:ultrastructure; D010316:Particle Size; D010455:Peptides / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011791:Quartz / Q000737:chemistry; D053838:Scattering, Small Angle; D055672:Static Electricity; D014961:X-Ray Diffraction
chemical_list: D000464:Alginates; D005290:Ferric Compounds; D006603:Hexuronic Acids; D010455:Peptides; D011791:Quartz; C017645:polyaspartate; C021024:ferric hydroxide; D020723:Glucuronic Acid