Formation of a nanoparticulate birnessite-like phase in purported molecular water oxidation catalyst systems

Hocking, Rosalie K., Malaeb, Rafah, Gates, Will P., Patti, Antonio F., Chang, Shery L.Y., Devlin, Glyn, MacFarlane, Douglas R., and Spiccia, Leone (2014) Formation of a nanoparticulate birnessite-like phase in purported molecular water oxidation catalyst systems. ChemCatChem, 6 (7). pp. 2028-2038.

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Abstract

The fate of [Mn-2^(III/IV)(μ-O)(2)(terpy)(2)(H2O)(2)]^3+ (1) under conditions typically applied to test its ability to catalyze water oxidation was studied by X-ray absorption spectroscopy and UV/Vis spectrophotometry by using [Mn-2^(III/IV)(μ-O)(2)(bipy)(4)]^3+ (2) and Mn^2+ as controls (terpy= 2,2':6',2"-terpyridine, bipy=2,2'-bipyridine). The sample matrix, pH and choice of oxidizing agent were found to have a significant effect on the species formed under catalytic conditions. At low range pH values (4-6), homogeneous catalysis testing in oxone implied that 1 remains intact, whereas in clay intercalate there is strong evidence that 1 breaks down to a birnessite-like phase. In homogeneous solutions at higher pH, the results are consistent with the same birnessite-like structure identified in the clay intercalate. The use of the molecular complexes, as a source of manganese instead of simple MnII salts, was found to have the effect of slowing down oxide formation and particle aggregation in solution. The original analytical results that implied the systems are molecular are discussed in the context of these new observations.

Item ID: 36136
Item Type: Article (Research - C1)
ISSN: 1867-3899
Keywords: homogeneous catalysis, manganese, oxidation, water chemistry, X-ray absorption spectroscopy
Funders: Australian Research Council (ARC), Australian Centre for Excellence for Electromaterials Science (ACES), James Cook University (JCU)
Date Deposited: 12 Nov 2014 10:54
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030201 Bioinorganic Chemistry @ 70%
04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 30%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 70%
97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 20%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 10%
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