TY - JOUR
T1 - Pathways for the Photoreduction of Fumarate on ZnS
AU - Mangiante, David
AU - Schaller, Richard Daniel
AU - Banfield, Jillian F.
AU - Gilbert, Benjamin
N1 - Funding Information:
This work was funded by the NSF Geobiology and Low-Temperature Geochemistry program under Grant No. 1324791. B.G. was supported by the Department of Energy (DOE), Office of Basic Energy Sciences (BES) under Contract No. DE-AC02-05CH11231. The use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/10/17
Y1 - 2019/10/17
N2 - Semiconductor mineral particles can act as photocatalysts for organic redox reactions that occur enzymatically in modern biological metabolic pathways. Semiconductor mineral-mediated photocatalysis may have contributed to the prebiotic synthesis of organic acids on the early Earth, but assessing the plausibility of this hypothesis is impeded by the lack of knowledge about the mechanisms for light-driven organic redox reactions on mineral surfaces. We selected one step in the reverse tricarboxylic acid (rTCA) cycle, the reduction of fumarate to succinate, that has been shown to be photocatalyzed by zinc sulfide (ZnS). Using static and time-resolved optical emission and absorption spectroscopy, we studied the adsorption of fumarate and the rates and pathways for charge transfer. We find that ZnS transfers photoexcited electrons to bound and dissolved fumarate on a wide range of time scales but not to succinate, supporting the concept that ZnS mediated photoreduction of fumarate could have operated in oceans of the early Earth. Optical transient absorption (TA) spectroscopy identified a signature tentatively attributed to the fumarate radical anion that is stable for at least 8 ns, providing evidence that fumarate photoreduction under solar illumination levels occurs by successive photoelectron transfer. The model for electronic excitation, relaxation, and interfacial charge-transfer processes in ZnS provided here will inform all future studies of the photochemical reactions of this mineral.
AB - Semiconductor mineral particles can act as photocatalysts for organic redox reactions that occur enzymatically in modern biological metabolic pathways. Semiconductor mineral-mediated photocatalysis may have contributed to the prebiotic synthesis of organic acids on the early Earth, but assessing the plausibility of this hypothesis is impeded by the lack of knowledge about the mechanisms for light-driven organic redox reactions on mineral surfaces. We selected one step in the reverse tricarboxylic acid (rTCA) cycle, the reduction of fumarate to succinate, that has been shown to be photocatalyzed by zinc sulfide (ZnS). Using static and time-resolved optical emission and absorption spectroscopy, we studied the adsorption of fumarate and the rates and pathways for charge transfer. We find that ZnS transfers photoexcited electrons to bound and dissolved fumarate on a wide range of time scales but not to succinate, supporting the concept that ZnS mediated photoreduction of fumarate could have operated in oceans of the early Earth. Optical transient absorption (TA) spectroscopy identified a signature tentatively attributed to the fumarate radical anion that is stable for at least 8 ns, providing evidence that fumarate photoreduction under solar illumination levels occurs by successive photoelectron transfer. The model for electronic excitation, relaxation, and interfacial charge-transfer processes in ZnS provided here will inform all future studies of the photochemical reactions of this mineral.
KW - Carbon cycle
KW - Carbon dioxide
KW - Mineralization
KW - Photochemistry
KW - Ultrafast spectroscopy
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U2 - 10.1021/acsearthspacechem.9b00169
DO - 10.1021/acsearthspacechem.9b00169
M3 - Article
AN - SCOPUS:85072556113
VL - 3
SP - 2250
EP - 2258
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
SN - 2472-3452
IS - 10
ER -