We are developing Co3O4 core - silica shell nanotubes for closing the photosynthetic cycle of carbon dioxide reduction and water oxidation on the nanoscale. The construct consisting of robust inorganic molecular light absorbers and metal oxide catalysts is designed to separate the spaces of O2 evolution from those of light absorption and the reduction chemistry. The presentation will focus on the mechanism of visible light sensitized water oxidation on the Co3O4 surface in aqueous solution, which features the first direct observation of two surface intermediates using time-resolved rapid-scan ATR-FT-infrared spectroscopy, namely a superoxide and an oxo cobalt intermediate. The temporal behavior in response to a photolysis pulse indicates that the oxo cobalt (1-electron oxidation) intermediate undergoes spontaneous OO bond formation. The superoxo (3-electron) intermediate persists until the arrival of another charge (hole) that results in the elimination of O2. 18O isotopic composition of the final O2 product mirrors that of the surface intermediates. On the reductive side, new visible light absorbing binuclear charge transfer units such as ZrOCo for CO2 conversion to CO and formate have been discovered and their photophysical and catalytic properties characterized. Progress in the assembly of the complete photosynthetic units and spectroscopic characterization of charge transport pathways will be presented. This includes monitoring of hole transport across the separating silica nanolayer via embedded molecular wires by transient optical spectroscopy.

Co oxide nanotubes as water oxidation catalysts in artificial photosynthetic units

246th National Meeting (2013)

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