title: Influence of 300°C thermal conversion of Fe-Ce hydrous oxides prepared by hydrothermal precipitation on the adsorptive performance of five anions: Insights from EXAFS/XANES, XRD and FTIR (companion paper).
abstract: In this work, we report atomic-scale reconstruction processes in Fe-Ce oxide-based composites (hydrothermally precipitated at Fe-to-Ce dosage ratios of 1:0, 2:1, 1:1, 1:2, and 0:1), upon treatment at 300°C. The structural changes are correlated with the adsorptive removal of arsenate, phosphate, fluoride, bromide, and bromate. The presence of the carbonate-based Ce-component and surface sulfate in precursor samples creates favorable conditions for phase transformation, resulting in the formation of novel (unknown) layered compounds of Fe and Ce. These compounds are of the layered double hydroxide type, with sulfate in the interlayer space. In spite of general awareness of the importance of surface area in adsorptive removal, the increase in surface area upon thermal treatment did not increase adsorption of the studied anions. However, EXAFS simulations and the adsorption tests provided evidence of regularities between local structures of Fe in composites obtained at 80 and 300°C and adsorption performance of most studied anions. The best adsorption of tetrahedral anions was demonstrated by samples whose simulated outer Fe shells resulted from oscillations from both O and Fe atoms. In contrast, the loss of extended x-ray absorption fine structure was correlated with the decrease of adsorptive removal. Both Fe K-edge and Ce L3-edge EXAFS suggested the formation of solid solutions. For the first time, the utilization of extended x-ray absorption fine structure is suggested as a methodological approach (first expressed in the companion paper) to estimate the surface reactivity of inorganic materials intended for use as anion exchange adsorbents.
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands; School of Engineering and Built Environment, Glasgow Caledonian University, Cowcaddens Road 70, Glasgow G40BA, United Kingdom. Electronic address: Natalia.Chubar@gcu.ac.uk.
authors.forename: Natalia
authors.initials: N
authors.lastname: Chubar
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands; Faculty of Chemistry, Kyiv National Taras Shevchenko University, 12 L. Tolstogo Str., 01033 Kyiv, Ukraine.
authors.forename: Vasyl
authors.initials: V
authors.lastname: Gerda
authors.affiliation: Dutch-Belgian Beamline (DUBBLE), ESRF - The European Synchrotron CS 40220, 38043 Grenoble Cedex 9, France.
authors.forename: Dipanjan
authors.initials: D
authors.lastname: Banerjee
keywords: Adsorption; EXAFS; Fe and Ce hydrous oxides; Thermal conversion; Toxic anions; Urea precipitation