Ca(2+) -Induced Oxygen Generation by FeO4(2-) at pH 9-10

Area of Science:

• Environmental Chemistry
• Inorganic Chemistry
• Oxidation Chemistry

Background:

• Ferrate(VI) (FeO4(2-)) is a potent oxidant, but unstable in acidic conditions.
• At alkaline pH (9-10), ferrate(VI) is relatively stable, with minimal decomposition.
• Understanding ferrate(VI) stability and activation is crucial for its application in water treatment.

Purpose of the Study:

• To investigate the activation mechanism of ferrate(VI) by divalent cations at alkaline pH.
• To elucidate the role of Ca(2+) in the decomposition of ferrate(VI) and O2 generation.
• To explore the influence of other alkaline earth metal ions on ferrate(VI) stability.

Main Methods:

• Kinetic studies to determine the rate law for O2 generation.
• Isotopic labeling experiments ((18)O) to trace oxygen atom origins.
• Density Functional Theory (DFT) calculations to model reaction mechanisms.

Main Results:

• Ferrate(VI) is activated by Ca(2+) at pH 9-10, leading to O2 production.
• The reaction follows the rate law: d[O2]/dt = kCa[Ca(2+)][FeO4(2-)](2).
• (18)O-labeling confirmed both oxygen atoms in O2 originate from ferrate(VI), suggesting O-O coupling.

Conclusions:

• Divalent cations, particularly Ca(2+), act as catalysts for ferrate(VI) decomposition at alkaline pH.
• Ca(2+) facilitates O-O coupling between two ferrate(VI) ions by bridging them.
• Mg(2+) and Sr(2+) exhibit similar activating effects, indicating a general mechanism for alkaline earth metal ions.