TY - JOUR
T1 - Effect of Fe oxidation state (+2 versus +3) in precursor on the structure of Fe oxides/carbonates-based composites examined by XPS, FTIR and EXAFS
AU - Chubar, Natalia
AU - Gerda, Vasyl
AU - Szlachta, Malgorzata
AU - Yablokova, Ganna
N1 - Funding Information:
King Abdullah University of Science and Technology ( KAUST ) (Saudi Arabia), which funded this research via the Global Research Partnership program (renamed for Global Collaborative Research) (award № KUK-C1-017-12 ), and Dutch Research Council ( NWO ) (Netherlands), which financed EXAFS/XANES studies at Dutch-Belgian Beamline (DUBBLE) in 2010 at the European Synchrotron Radiation Facility (ESRF) (France), are gratefully acknowledged. The authors thank Dr. Andrey Shchukarev (Umeå University, Sweden) for XPS analysis and all XPS spectra treatments (deconvolutions). The authors are much obliged to Editor and anonymous Reviewers for their helpful comments which resulted in the improved paper.
Publisher Copyright:
© 2021 The Authors
PY - 2021/11
Y1 - 2021/11
N2 - Here we investigate the influence of Fe oxidation state (either Fe(II) or Fe(III) sulfates) in precursor of the same chemical composition on the atomic scale structure, surface speciation and adsorptive anion removal of the purely inorganic composites produced under the urea supported hydrothermal synthesis. In case of utilization of Fe3+ precursor, the materials chemistry was solely dominated by the formation of highly crystalline Fe(III) oxides, however the particle surfaces were covered with small quantities of FeCO3 (not detectable by EXAFS/XANES/FTIR) precipitated after the autoclave was turned off. Within the reactive medium with Fe2+ precursor, due to high pressure in autoclave which facilitated reducing conditions and sedimentation of Fe divalent, two main processes took place one of which was the formation of Fe hydrous oxides; the second reaction resulted in generation of FeCO3, which become a predominant phase in volume averaged composition. Notably, despite the prevalence of Fe(II) carbonates in bulk structure, the narrow upper layers (XPS detectable) was enriched with Fe(III) oxides. At the chosen autoclave temperature of 150 °C, both samples had low hydration of physisorbed water, which confirmed our recent hypothesis about correlation between Fe (or another metal formed oxides) local structure in outer shells fitted with several (many) oxygen atoms and the material hydration with physisorbed water. None of the two composites demonstrated strong adsorptive removal of seven anions (F−, Br−, BrO3−, HAsO42−, H3AsO3, HPO42−, SeO42−), which verified another idea about the interdependence of distinguished (EXAFS simulated) outer shells of metals (here, Fe) fitted with two paths simultaneously ({Fe–Fe}+{Fe–O}) one peak and the anion exchange potential. Overall, the Fe(III)-precursor product was more crystalline, less heterogeneous (fewer phases), showed worse anion uptake than the other sample. The material prepared from Fe(II) precursor is considered to be a promising precursor for further phase transformations via thermal or hydrothermal treatments (due to generous presence of FeCO3).
AB - Here we investigate the influence of Fe oxidation state (either Fe(II) or Fe(III) sulfates) in precursor of the same chemical composition on the atomic scale structure, surface speciation and adsorptive anion removal of the purely inorganic composites produced under the urea supported hydrothermal synthesis. In case of utilization of Fe3+ precursor, the materials chemistry was solely dominated by the formation of highly crystalline Fe(III) oxides, however the particle surfaces were covered with small quantities of FeCO3 (not detectable by EXAFS/XANES/FTIR) precipitated after the autoclave was turned off. Within the reactive medium with Fe2+ precursor, due to high pressure in autoclave which facilitated reducing conditions and sedimentation of Fe divalent, two main processes took place one of which was the formation of Fe hydrous oxides; the second reaction resulted in generation of FeCO3, which become a predominant phase in volume averaged composition. Notably, despite the prevalence of Fe(II) carbonates in bulk structure, the narrow upper layers (XPS detectable) was enriched with Fe(III) oxides. At the chosen autoclave temperature of 150 °C, both samples had low hydration of physisorbed water, which confirmed our recent hypothesis about correlation between Fe (or another metal formed oxides) local structure in outer shells fitted with several (many) oxygen atoms and the material hydration with physisorbed water. None of the two composites demonstrated strong adsorptive removal of seven anions (F−, Br−, BrO3−, HAsO42−, H3AsO3, HPO42−, SeO42−), which verified another idea about the interdependence of distinguished (EXAFS simulated) outer shells of metals (here, Fe) fitted with two paths simultaneously ({Fe–Fe}+{Fe–O}) one peak and the anion exchange potential. Overall, the Fe(III)-precursor product was more crystalline, less heterogeneous (fewer phases), showed worse anion uptake than the other sample. The material prepared from Fe(II) precursor is considered to be a promising precursor for further phase transformations via thermal or hydrothermal treatments (due to generous presence of FeCO3).
KW - EXAFS (Extended x-ray absorption fine structure)
KW - Hydrothermal urea-supported precipitation
KW - Iron oxides/carbonates-based composites
KW - Sorption of anions
KW - XPS (X-ray photoelectron spectroscopy)
UR - http://www.scopus.com/inward/record.url?scp=85117263120&partnerID=8YFLogxK
U2 - 10.1016/j.solidstatesciences.2021.106752
DO - 10.1016/j.solidstatesciences.2021.106752
M3 - Article
SN - 1293-2558
VL - 121
SP - 1
EP - 13
JO - Solid State Sciences
JF - Solid State Sciences
M1 - 106752
ER -