Tomoyuki Tajima

Photosensitized hydrogen evolution from water using a single-walled carbon nanotube/fullerodendron/SiO2 coaxial nanohybrid.

A coaxial nanohybrid consisting of a single-walled carbon nanotube (SWCNT), fullerodendron, and SiO(2) shows high-efficiency light-driven hydrogen evolution from water. Upon visible light irradiation, SWCNT/fullerodendron/SiO(2) coaxial nanohybrid shows hydrogen evolution activity in the presence of methyl viologen (MV(2+)), benzyldihydronicotinamide (BNAH), and a colloidal polyvinyl alcohol(PVA)-Pt.

Synthetic analogues of [Fe4S4(Cys)3(His)] in hydrogenases and [Fe4S4(Cys)4] in HiPIP derived from all-ferric [Fe4S4{N(SiMe3)2}4]

The all-ferric [Fe4S4]4+ cluster [Fe4S4{N(SiMe3)2}4] 1 and its one-electron reduced form [1]- serve as convenient precursors for the synthesis of 3∶1-site differentiated [Fe4S4] clusters and high-potential iron-sulfur protein (HiPIP) model clusters. The reaction of 1 with four equivalents (equiv) of the bulky thiol HSDmp (Dmp = 2,6-(mesityl)2C6H3, mesityl = 2,4,6-Me3C6H2) followed by treatment with tetrahydrofuran (THF) resulted in the isolation of [Fe4S4(SDmp)3(THF)3] 2. Cluster 2 contains an octahedral iron atom with three THF ligands, and its Fe(S)3(O)3 coordination environment is relevant to that in the active site of substrate-bound aconitase. An analogous reaction of [1]- with four equiv of HSDmp gave [Fe4S4(SDmp)4]- 3, which models the oxidized form of HiPIP. The THF ligands in 2 can be replaced by tetramethyl-imidazole (Me4Im) to give [Fe4S4(SDmp)3(Me4Im)] 4 modeling the [Fe4S4(Cys)3(His)] cluster in hydrogenases, and its one-electron reduced form [4]- was synthesized from the reaction of 3 with Me4Im. The reversible redox couple between 3 and [3]- was observed at E1/2 = -820 mV vs. Ag/Ag+, and the corresponding reversible couple for 4 and [4]- is positively shifted by +440 mV. The cyclic voltammogram of 3 also exhibited a reversible oxidation couple, which indicates generation of the all-ferric [Fe4S4]4+ cluster, [Fe4S4(SDmp)4].

A Convenient Route to Synthetic Analogues of the Oxidized Form of High-Potential Iron–Sulfur Proteins

An amide-bound [Fe4S4](3+) cluster, [Fe4S4{N(SiMe3)2}4](-) (1), was found to serve as a convenient precursor for synthetic analogues of the oxidized form of high-potential iron-sulfur proteins. Treatment of 1 with 4 equiv of bulky thiols led to replacement of the amide ligands with thiolates, giving rise to a series of [Fe4S4(SR)4](-) clusters (R = Dmp (2a), Tbt (2b), Eind (2c), Dxp (2d), Dpp (2e); Dmp = 2,6-di(mesityl)phenyl, Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl, Dxp = 2,6-di(m-xylyl)phenyl, Dpp = 2,6-diphenylphenyl). These clusters were characterized by the mass spectrum, the EPR spectrum, and X-ray crystallography. The redox potentials of the [Fe4S4](3+/2+) couple, -0.82 V (2a), -0.86 V (2b), -0.84 V (2c), -0.74 V (2d), and -0.63 V (2e) vs Ag/Ag(+) in THF, are significantly more negative than that of [Fe4S4(SPh)4](-/2-) (-0.21 V).

SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100u2009meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QYu2009=u20090.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

Spectroscopic Characterization of Nanohybrids Consisting of Single-walled Carbon Nanotubes and Fullerodendron

Hydrogen gas, which can be used in fuel cells to generate electricity, is considered the ultimate clean energy source. Recently, it was reported that a photo-induced electron transfer system consisting of single-walled carbon nanotubes (SWCNTs) and fullerodendrons shows photo-catalytic activity with a very high quantum yield for splitting water under visible light irradiation. However, the mechanism of high efficiency hydrogen generation is not yet clearly understood. We report here the spectroscopic characterizations of the SWCNT-fullerodendron composites. The results indicate two important fundamental properties of the composite system. First, fullerodendrons preferentially interact with the semiconducting SWCNTs instead of with their metallic counterparts. Second, the photo-induced electron transfer process from the C60 moiety of fullerodendrons to SWCNTs occurs more efficiently with an increasing tube diameter.

Photosensitized hydrogen evolution from water using single-walled carbon nanotube/fullerodendron/Pt(II) coaxial nanohybrids

Direct incorporation of a Pt(II) complex into the shell of SWCNT/fullerodendron coaxial nanohybrids produces a new coaxial nanowire, SWCNT/fullerodendron/Pt(II), that shows efficient photocatalytic activity for hydrogen evolution from water (Φ = 0.16 upon irradiation at 450 ± 5 nm) without any aid of electron relay such as methyl viologen.

Incorporating a TiOx shell in single-walled carbon nanotube/fullerodendron coaxial nanowires: increasing the photocatalytic evolution of H2 from water under irradiation with visible light

A custom-tailored single-walled carbon nanotube (SWCNT) photocatalyst with an electron-extracting TiOx shell, i.e., a SWCNT/fullerodendron/TiOx coaxial nanowire, has been fabricated. Due to the presence of the TiOx shell, the SWCNT/fullerodendron/TiOx coaxial nanowire shows an enhanced photocatalytic activity (Φ = 0.47) for the evolution of hydrogen from water under irradiation with visible light (λ = 450 nm).

Enhanced Photosensitized Hydrogen Production by Encapsulation of Ferrocenyl Dyes into Single-Walled Carbon Nanotubes

Dye-encapsulated single-walled carbon nanotubes (SWCNTs) were employed for the construction of a coaxial three-component dye/SWCNT/C60 heterojunction. Despite the larger diameter (∼1.4 nm) of the SWCNTs relative to that set by Flavels rule (0.95 nm), the photoinduced electron transfer from dye-encapsulated SWCNTs to C60 proceeded smoothly, resulting in the photosensitized evolution of H2 from H2O using a ferrocenyl-based photosensitizer, which was confirmed by the action spectra.

Template-free fabrication of a cylindrical macropore array in SnO2

A simple sol–gel condensation of tin(IV) tert-butoxide led to the formation of meso/macroporous membranes. SEM observation clearly shows the cylindrical macropore array, of which mean pore diameter is controllable between 200 and 800 nm. The existence of slit-shaped mesopores (12 nm) was confirmed by a N2 adsorption–desorption experiment.

Preparation and Optical and Electrochemical Properties of Phthalocyanines with the Ttf Unit

Abstract Tetrathiafluvalene (TTF)-annulated symmetrical and unsymmetrical phthalocyanines (4), (5), and (6) were prepared from 3,6-dioctylphthalonitrile (1) with a TTF unit, 4,5-dioctyloxyphthalonitrile (2), and 3,6-dioctyloxyphthalonitrile (3). Tetra-TTF-annulated phthalocyanine (4) and iodine produced an electron transfer complex which showed a radical cationic character. GRAPHICAL ABSTRACT