Structural Properties of the Cr(III)-Fe(III) (Oxy)Hydroxide Compositional Series: Insights for a Nanomaterial “Solid Solution”
Chromium(III) (oxy)hydroxide and mixed Cr(III)-Fe(III) (oxy)hydroxides are environmentally important compounds for controlling chromium speciation and bioaccessibility in soils and aquatic systems and are also industrially important as precursors for materials and catalyst synthesis. However, direct characterization of the atomic arrangements of these materials is complicated because of their amorphous X-ray properties. This study involves synthesis of the complete Cr(III)-Fe(III) (oxy)hydroxide compositional series, and the use of complementary thermal, microscopic, spectroscopic, and scattering techniques for the evaluation of their structural properties. Thermal analysis results show that the Cr end member has a higher hydration state than the Fe end member, likely associated with the difference in water exchange rates in the first hydration spheres of Cr(III) and Fe(III). Three stages of weight loss are observed and are likely related to the loss of surface/structural water and hydroxyl groups. As compared to the Cr end member, the intermediate composition sample shows lower dehydration temperatures and a higher exothermic transition temperature. XANES analysis shows Cr(III) and Fe(III) to be the dominant oxidation states. XANES spectra also show progressive changes in the local structure around Cr and Fe atoms over the series. Pair distribution function (PDF) analysis of synchrotron X-ray total scattering data shows that the Fe end member is nanocrystalline ferrihydrite with an intermediate-range order and average coherent domain size of {approx}27 {angstrom}. The Cr end member, with a coherent domain size of {approx}10 {angstrom}, has only short-range order. The PDFs show progressive structural changes across the compositional series. High-resolution transmission electron microscopy (HRTEM) results also show the loss of structural order with increasing Cr content. These observations provide strong structural evidence of chemical substitution and progressive structural changes along the compositional series.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 985531
- Report Number(s):
- BNL-93874-2010-JA; CMATEX; R&D Project: NC-001; TRN: US1006163
- Journal Information:
- Chemistry of Materials, Vol. 22, Issue 12; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
ATOMS
CATALYSTS
CHROMIUM
DEHYDRATION
DISTRIBUTION FUNCTIONS
EVALUATION
FOREIGN EXCHANGE RATE
HYDRATION
SCATTERING
SOILS
SPECTRA
SYNCHROTRONS
SYNTHESIS
THERMAL ANALYSIS
TRANSITION TEMPERATURE
TRANSMISSION ELECTRON MICROSCOPY
VALENCE
WATER
Cr-Fe hydroxide
solid solution
functional nanomaterials