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Artificial Photosynthesis of C1–C3 Hydrocarbons from Water and CO_2 on Titanate Nanotubes Decorated with Nanoparticle Elemental Copper and CdS Quantum Dots

Park, Hyunwoong and Ou, Hsin-Hung and Colussi, Agustín J. and Hoffmann, Michael R. (2015) Artificial Photosynthesis of C1–C3 Hydrocarbons from Water and CO_2 on Titanate Nanotubes Decorated with Nanoparticle Elemental Copper and CdS Quantum Dots. Journal of Physical Chemistry A, 119 (19). pp. 4658-4666. ISSN 1089-5639.

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The conversion of CO_2 and water into value-added fuels with visible light is difficult to achieve in inorganic photocatalytic systems. However, we synthesized a ternary catalyst, CdS/(Cu-TNTs), which is assembled on a core of sodium trititanate nanotubes (TNTs; Na_xH_(2–x)Ti_3O_7) decorated with elemental copper deposits followed by an overcoat of CdS quantum dot deposits. This ternary photocatalyst is capable of catalyzing the conversion of CO_2 and water into C1–C3 hydrocarbons (e.g., CH_4, C_2H_6, C_3H_8, C_2H_4, C_3H_6) upon irradiation with visible light above 420 nm. With this composite photocatalyst, sacrificial electron donors are not required for the photoreduction of CO_2. We have shown that water is the principal photoexcited-state electron donor, while CO_2 bound to the composite surface serves as the corresponding electron acceptor. If the photochemical reaction is carried out under an atmosphere of 99.9% ^(13)CO_2, then the product hydrocarbons are built upon a ^(13)C backbone. However, free molecular H_2 is not observed over 5 h of visible light irradiation even though proton reduction in aqueous solution is thermodynamically favored over CO_2 reduction. In terms of photocatalytic efficiency, the stoichiometric fraction of Na^+ in TNTs appears to be an important factor that influences the formation of the observed hydrocarbons. The coordination of CO_2 to surface exchange sites on the ternary catalyst leads to the formation of surface-bound CO_2 and related carbonate species. It appears that the bidentate binding of O═C═O to certain reactive surface sites reduces the energy barrier for conduction band electron transfer to CO_2. The methyl radical (CH_3•), an observed intermediate in the reaction, was positively identified using an ESR spin trapping probe molecule. The copper deposits on the surface of TNTs appear to play a major role in the transient trapping of methyl radical, which in turn self-reacts to produce ethane.

Item Type:Article
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URLURL TypeDescription Information
Park, Hyunwoong0000-0002-4938-6907
Colussi, Agustín J.0000-0002-3400-4101
Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 2015 American Chemical Society. Received: November 12, 2014; Revised: January 21, 2015; Published: January 22, 2015. Special Issue: Mario Molina Festschrift. Research support was funded by a National Science Foundation grant awarded to M.R.H. (Grant No. CHE-0924597). We acknowledge Dr. Nathan Dalleska for helping gas composition analysis at the Environmental Analysis Center, Environmental Science and Technology of California Institute of Technology (Caltech). We also acknowledge the technical staffs for the assistance of EPR and XRD works in the Division of Chemistry and Chemical engineering of Caltech. XPS and DRIFT experiments were carried out at the Molecular Materials Research Center of the Beckman Institute of Caltech. H.P. is grateful to the Korea National Research Foundation (2013K2A1A2052901, 2014S1A2A2027802, and 2014M1A3A3A02034875), the Korea Center for Artificial Photosynthesis (KCAP) (No. 2009-0093880), and the Korea CCS R&D Center (KCRC) (No. 2014M1A8A1049354) for financial support, and the Seoul Broadcasting System (SBS) Foundation in support of his sabbatical leave at Caltech.
Funding AgencyGrant Number
Korea National Research Foundation2013K2A1A2052901
Korea National Research Foundation2014S1A2A2027802
Korea National Research Foundation2014M1A3A3A02034875
Korea Center for Artificial Photosynthesis (KCAP)2009-0093880
Korea CCS R&D Center (KCRC)2014M1A8A1049354
Seoul Broadcasting System (SBS)UNSPECIFIED
Issue or Number:19
Record Number:CaltechAUTHORS:20150616-152637347
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Official Citation:Artificial Photosynthesis of C1–C3 Hydrocarbons from Water and CO2 on Titanate Nanotubes Decorated with Nanoparticle Elemental Copper and CdS Quantum Dots Hyunwoong Park, Hsin-Hung Ou, Agustín J. Colussi, and Michael R. Hoffmann The Journal of Physical Chemistry A 2015 119 (19), 4658-4666 DOI: 10.1021/jp511329d
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58293
Deposited By: Tony Diaz
Deposited On:16 Jun 2015 23:22
Last Modified:09 Mar 2020 13:19

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