title: Hydrophilicity control of visible-light hydrogen evolution and dynamics of the charge-separated state in dye/TiO2/Pt hybrid systems.
abstract: Visible-light-driven H(2) evolution based on Dye/TiO(2)/Pt hybrid photocatalysts was investigated for a series of (E)-3-(5'-{4-[bis(4-R(1)-phenyl)amino]phenyl}-4,4'-(R(2))(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 R(1), varying in the order MOD (R(1)=CH(3)OCH(2), R(2)=H)≈MO4D (R(1)=R(2)=CH(3)OCH(2))>HD (R(1)=R(2)=H)>PD (R(1)=C(3)H(7), R(2)=H). In the case of MOD/TiO(2)/Pt, the apparent quantum yield for photocatalyzed H(2) generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD- or PD-grafted transparent films of TiO(2) 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 R(1) 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 H(2) 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.
authors.affiliation: Department of Advanced Materials Chemistry, Sejong, Korea University, 208 Seochang, Chochiwon, Chung-nam 339-700, Korea.
authors.forename: Won-Sik
authors.initials: WS
authors.lastname: Han
authors.forename: Kyung-Ryang
authors.initials: KR
authors.lastname: Wee
authors.forename: Hyun-Young
authors.initials: HY
authors.lastname: Kim
authors.forename: Chyongjin
authors.initials: C
authors.lastname: Pac
authors.forename: Yu
authors.initials: Y
authors.lastname: Nabetani
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamamoto
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Shimada
authors.forename: Haruo
authors.initials: H
authors.lastname: Inoue
authors.forename: Heesung
authors.initials: H
authors.lastname: Choi
authors.forename: Kyeongjae
authors.initials: K
authors.lastname: Cho
authors.forename: Sang Ook
authors.initials: SO
authors.lastname: Kang