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Manganese Oxide Nanoparticle Synthesis by Thermal Decomposition of Manganese(II) Acetylacetonate
Published on: June 18, 2020
Chromium(III) oxidation by three poorly crystalline manganese(IV) oxides. 2. Solid phase analyses
Gautier Landrot1, Matthew Ginder-Vogel, Kenneth Livi
1Plant and Soil Sciences Department, Delaware Environmental Institute, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, USA. glandrot@gmail.com
Environmental Science & Technology
|October 12, 2012
Summary
Layered manganese (IV) oxide minerals oxidize chromium (III) to toxic chromium (VI). This study reveals chromium (III) tightly binds to mineral surfaces, halting further oxidation, contrary to precipitate formation theories.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Layered, poorly crystalline manganese (IV) oxide (MnO2) phases are common in soils.
- These minerals can oxidize chromium (III) to the more mobile and toxic chromium (VI).
- The molecular mechanisms of Cr(III) oxidation by MnO2 are not well understood.
Purpose of the Study:
- To investigate the sorption mechanisms of Cr(III) and Cr(VI) on synthetic MnO2 phases.
- To elucidate the microscopic and molecular processes governing Cr(III) oxidation by MnO2.
Main Methods:
- Utilized Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS).
- Analyzed three synthetic MnO2 phases: Random Stacked Birnessite (RSB), δ-MnO2, and Acid Birnessite (AB).
- Reacted MnO2 with Cr(III) at varying pH levels (2.5, 3, 3.5).
Main Results:
- Cr(VI) sorbed as a loosely bound outer-sphere complex on MnO2.
- Cr(III) sorbed as a tightly bound inner-sphere complex on MnO2.
- Cr(III) oxidation by MnO2 ceased within 30 minutes under most conditions, without detectable Cr surface precipitate formation.
Conclusions:
- Cr(III) sorption as an inner-sphere complex likely inhibits further oxidation by MnO2.
- The cessation of Cr(III) oxidation is not necessarily due to surface precipitate formation.
- Further research is required to fully understand the Cr(III) oxidation kinetics and mechanisms by MnO2.
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