Sol-gel route to the tunneled manganese oxide cryptomelane

Journal Article · Sat Mar 01 04:00:00 EST 1997 · Chemistry of Materials

DOI:https://doi.org/10.1021/cm960460k· OSTI ID:569179

Ching, S; Roark, J L ^[1]; Duan, N; Suib, S L ^[2]

---

1. Connecticut College, New London, CT (United States)
2. Univ. of Connecticut, Storr, CT (United States)

The sol-gel reaction between KMnO{sub 4} and fumaric acid in a 3:1 mole ratio generates a flocculant gel that serves as a precursor to the tunneled manganese oxide, cryptomelane. The elemental composition of sol-gel cryptomelane has been determined to be K{sub 0.12}MnO{sub 2.0-} (H{sub 2}O){sub 0.09}. Further characterization has been performed using powder X-ray diffraction, scanning electron microscopy, and Auger electron spectroscopy. The sol-gel process is heavily dependent on reactant concentration. Solutions that are too concentrated produce the layered manganese oxide birnessite, whereas overly dilute reactions yield mixtures of cryptomelane and Mn{sub 2}O{sub 3}. The preference for cryptomelane over birnessite correlates with low potassium content in the gel. The sol-gel procedure for synthesizing cryptomelane is not easily transferred to the preparation of analogous manganese oxides with different tunnel cations. Reactions that employ permanganates other than KMnO{sub 4} generally yield Mn{sub 2}O{sub 3}, with cryptomelane being a minor product at best. Thermal analyses of cryptomelane gels indicate that calcination proceeds through a series of stages that involve loss of water, loss of residual organics, conversion to cryptomelane, and finally degradation to Mn{sub 3}O{sub 4}. The extraction of potassium ions from sol-gel cryptomelane by various foreign cations is minimal, with the loss of K{sup +} being on the order of 10%. 49 refs., 7 figs., 3 tabs.

• OSTI ID: 569179
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 3 Vol. 9; ISSN 0897-4756; ISSN CMATEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
AUGER ELECTRON SPECTROSCOPY
CALCINATION
CATIONS
CHEMICAL COMPOSITION
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
FUMARIC ACID
HOLLANDITE
MANGANESE OXIDES
MOLECULAR STRUCTURE
PERMANGANATES
POROSITY
POTASSIUM
SCANNING ELECTRON MICROSCOPY
SOL-GEL PROCESS
STOICHIOMETRY
STRUCTURAL CHEMICAL ANALYSIS
SYNTHESIS
VALENCE
X-RAY DIFFRACTION