title: An X-ray absorption study of synthesis- and As adsorption-induced microstructural modifications in Fe oxy-hydroxides.
abstract: Synthetic adsorbents based on Fe oxy-hydroxides (FeOOH) prepared under a wide range of pH-values via intense oxidation conditions of FeSO4 as well as the As(III) and As(V) adsorption mechanism are investigated using X-ray absorption fine structure (XAFS) spectroscopies at the Fe- and As-K-edges. Synthesis in an alkaline environment promotes the face-connectivity of the Fe(O,OH)6 chains at the expense of edge- and corner-sharing linkage, which is consistent with the lower surface charge density and in turn with the lower arsenic adsorption capacity. Microstructural changes are also detected after As(V) adsorption onto FeOOH synthesized at pH 5.5: the ratio of face-/edge-sharing sites increases from approximately 0.4-0.7 as a function of the As(V)-loading. This modification of the polymeric Fe(O,OH)6 structure at higher As/Fe ratios is attributed to strong As(V) bidentate mononuclear ((2)E) and binuclear ((2)C) adsorption. In contrast, no alterations in the FeOOH microstructure were observed, possibly due to the weaker (2)E linkage of As(III).
authors.affiliation: Aristotle University of Thessaloniki, Department of Chemical Engineering, Analytical Chemistry Laboratory, Thessaloniki, 54124, Greece. Electronic address: fpina@physics.auth.gr.
authors.forename: F
authors.initials: F
authors.lastname: Pinakidou
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Katsikini
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: K
authors.initials: K
authors.lastname: Simeonidis
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: E C
authors.initials: EC
authors.lastname: Paloura
authors.affiliation: Aristotle University of Thessaloniki, Department of Chemical Engineering, Analytical Chemistry Laboratory, Thessaloniki, 54124, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Mitrakas
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000737:chemistry* / Q000302:isolation & purification; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides; D008958:Models, Molecular; D011108:Polymers; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D006878:Hydroxides; D011108:Polymers; C021024:ferric hydroxide; D001151:Arsenic
keywords: EXAFS; Fe oxy-hydroxides; NEXAFS; arsenic adsorption; microstructure; synthesis