Amorphous iron-(hydr) oxide networks at liquid/vapor interfaces: In situ X-ray scattering and spectroscopy studies

TitleAmorphous iron-(hydr) oxide networks at liquid/vapor interfaces: In situ X-ray scattering and spectroscopy studies
Publication TypeJournal Article
Year of Publication2012
AuthorsWang WJ, Pleasants J, Bu W, Park RY, Kuzmenko I, Vaknin D
Journal TitleJournal of Colloid and Interface Science
Volume384
Pages45-54
Date Published10
Type of ArticleArticle
ISBN Number0021-9797
Accession NumberWOS:000308337700006
Keywordsacid monolayers, air-water-interface, air/water interface, bacterial protein, Bio-inspired materials, charged interfaces, Charged templates, distributions, fluorescence, ion, Iron (hydr) oxide, iron-binding, langmuir monolayers, magnetite nanoparticles, Mms6, Organic growth, reflectivity, Surface-XANES, templates for inorganic materials, x-ray, X-ray fluorescence
Abstract

Surface sensitive X-ray reflectivity (XR), fluorescence (XF), and grazing incidence X-ray diffraction (GIXD) experiments were conducted to determine the accumulation of ferric iron Fe (III) or ferrous iron Fe (II) under dihexadecyl phosphate (DHDP) or arachidic acid (AA) Langmuir monolayers at liquid/vapor interfaces. Analysis of the X-ray reflectivity and fluorescence data of monolayers on the aqueous subphases containing FeCl3 indicates remarkably high levels of surface-bound Fe (III) in number of Fe3+ ions per molecule (DHDP or AA) that exceed the amount necessary to neutralize a hypothetically completely deprotonated monolayer (DHDP or AA). These results suggest that nano-scale iron (hydr) oxide complexes (oxides, hydroxides or oxyhydroxides) bind to the headgroups and effectively overcompensate the maximum possible charges at the interface. The lack of evidence of in-plane ordering in GIXD measurements and strong effects on the surface-pressure versus molecular area isotherms indicate that an amorphous network of iron (hydr) oxide complexes contiguous to the headgroups is formed. Similar experiments with FeCl2 generally resulted with the oxidation of Fe (II)-Fe (III) which consequently leads to ferric Fe (III) complexes binding albeit with less iron at the interface. Controlling the oxidation of Fe (II) changes the nature and amount of binding significantly. The implications to biomineralization of iron (hydr) oxides are briefly discussed. (C) 2012 Elsevier Inc. All rights reserved.

URL<Go to ISI>://WOS:000308337700006
DOI10.1016/j.jcis.2012.06.024
Alternate JournalJ. Colloid Interface Sci.