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Formation of a Nanoparticulate Birnessite‐Like Phase in Purported Molecular Water Oxidation Catalyst Systems
Author(s) -
Hocking Rosalie K.,
Malaeb Rafah,
Gates Will P.,
Patti Antonio F.,
Chang Shery L. Y.,
Devlin Glyn,
MacFarlane Douglas R.,
Spiccia Leone
Publication year - 2014
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201400066
Subject(s) - birnessite , chemistry , intercalation (chemistry) , catalysis , oxidizing agent , inorganic chemistry , manganese , context (archaeology) , phase (matter) , organic chemistry , manganese oxide , paleontology , biology
Abstract The fate of [Mn III/IV 2 (μ‐O) 2 (terpy) 2 (H 2 O) 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 III/IV 2 (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 Mn II 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.