Hydrophilicity Control of Visible‐Light Hydrogen Evolution and Dynamics of the Charge‐Separated State in Dye/TiO2/Pt Hybrid Systems |
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Authors: | Won‐Sik Han Kyung‐Ryang Wee Hyun‐Young Kim Prof. Chyongjin Pac Yu Nabetani Daisuke Yamamoto Tetsuya Shimada Prof. Haruo Inoue Heesung Choi Prof. Kyeongjae Cho Prof. Sang Ook Kang |
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Affiliation: | 1. Department of Advanced Materials Chemistry, Sejong, Korea University, 208 Seochang, Chochiwon, Chung‐nam 339‐700 (Korea), Fax: (+82)?44‐867‐5396;2. Yulchon Research Center, Sejong, Korea University, 208 Seochang, Chochiwon, Chung‐nam 339‐700 (Korea), Fax: (+82)?44‐867‐5396;3. Department of Applied Chemistry, Graduate Course of Urban Environmental Sciences, Tokyo Metropolitan University, Minami‐ohsawa 1‐1, Hachiohji, Tokyo 192‐0397 (Japan), Fax: (+81)‐426‐77‐2525;4. Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (USA);5. WCU Multiscale Mechanical Design Division, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151‐742 (Korea) |
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Abstract: | Visible‐light‐driven H2 evolution based on Dye/TiO2/Pt hybrid photocatalysts was investigated for a series of (E)‐3‐(5′‐{4‐[bis(4‐R1‐phenyl)amino]phenyl}‐4,4′‐(R2)2‐2,2′‐bithiophen‐5‐yl)‐2‐cyanoacrylic acid dyes. Efficiencies of hydrogen evolution from aqueous suspensions in the presence of ethylenediaminetetraacetic acid as electron donor under illumination at λ>420 nm were found to considerably depend on the hydrophilic character of R1, varying in the order MOD (R1=CH3OCH2, R2=H)≈ MO4D (R1=R2=CH3OCH2)> HD (R1=R2=H)> PD (R1=C3H7, R2=H). In the case of MOD /TiO2/Pt, the apparent quantum yield for photocatalyzed H2 generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD ‐ or PD ‐grafted transparent films of TiO2 nanoparticles dipped into water at pH 3 commonly revealed ultrafast formation (<100 fs) of the dye radical cation (Dye.+) followed by multicomponent decays, which involve minor fast decays (<5 ps) almost independent of R1 and major slower decays with significant differences between the two samples: 1) the early decay of the major components for MOD is about 2.5 times slower than that for PD and 2) a redshift of the spectrum occurred for MOD with a time constant of 17 ps, but not for PD . The substituent effects on H2 generation as well as on transient behavior have been discussed in terms substituent‐dependent charge recombination (CR) of Dye.+ with electrons in bulk, inner‐trap, and/or interstitial‐trap states, arising from different solvent reorganization. |
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Keywords: | charge transfer dyes/pigments hydrogen photosynthesis water chemistry |
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