Shinya Higashimoto

Characteristics of the charge transfer surface complex on titanium( iv ) dioxide for the visible light induced chemo-selective oxidation of benzyl alcohol

This paper deals with the oxidation of benzyl alcohol by O2 on pure TiO2 under visible light irradiation, and it was found that the benzyl alcohol is converted into benzaldehyde with high selectivity (>99%). In order to understand the origins of the visible light induced photocatalysis, surface characterizations of the charge transfer complex formed by the interaction of benzyl alcohol with the TiO2 was extensively performed by investigating the effect of heat-treatment on TiO2 or its chemical modification with hydrofluoric acid. Moreover, the study of the kinetic isotope effect (KIE) for the oxidation of benzyl alcohol showed that the α-deprotonation from benzyl alcohol is the rate determining step (RDS), the process of which is assisted by the terminal OH groups of TiO2. Photo-electrochemical investigations were also incorporated to demonstrate the reaction mechanism behind the visible light induced photocatalytic reaction.

Photocharge-Discharge Behaviors of Hybrid WO3 ∕ TiO2 Film Electrodes Conversion, Storage of Electrons, and the Effect of the W O 3 Structure on Rechargeability

Photoelectrochemical energy conversion and electron storage were investigated on hybrid WO 3 /TiO 2 film electrodes. Photoexcitation of WO 3 /TiO 2 was observed to undergo charge accumulation, i.e., double injection of electrons and protons into WO 3 to form tungsten bronze by the oxidation of oxalic acid or methanol to form CO 2 . It was clearly indicated that hybrid WO 3 /TiO 2 involving highly dispersed WO 3 (an amorphous-like WO 3 phase) exhibits more effective reversibility for photocharge-discharge processes than a hybrid involving a bulk polycrystalline WO 3 . The energy band structure and phase changes of WO 3 into tungsten bronze (H 0.23 WO 3 and H 0.33 WO 3 ) by photocharge or electrocharge of the hybrid WO 3 /TiO 2 have also been characterized.

Characterization and photocatalytic reactivities of Cr-HMS mesoporous molecular sieves.

Investigations of the local structures and photocatalytic reactivity of Cr-containing mesoporous molecular sieves (CrHMS) have been carried out. Cr-HMS involves tetrahedrally coordinated Cr-oxide species which are highly dispersed and incorporated with terminal Cr=O groups in the framework of molecular sieves. On the other hand, the imp-Cr/HMS prepared by an impregnation method consists of both tetrahedrally and octahedrally coordinated Cr-oxide species. The Cr-HMS exhibits much higher photocatalytic reactivity under UV irradiation for the isomerization of cis-2-butene than the imp-Cr/HMS and Cr-silicalite microporous catalysts. The charge transfer excited state of the tetrahedrally coordinated Cr-oxide species plays a significant role in the photocatalytic reaction. 453

Selective dehydrogenation of aromatic alcohols photocatalyzed by Pd-deposited CdS–TiO2 in aqueous solution using visible light

A CdS/TiO2 photocatalyst modified with a Pd co-catalyst was applied to a photocatalytic system for the selective dehydrogenation of benzyl alcohol to benzaldehyde with high selectivity (>99%) accompanied by the formation of H2 in aqueous solution under visible-light irradiation.

One-pot synthesis of imine from benzyl alcohol and nitrobenzene on visible-light responsive CdS–TiO2 photocatalysts

The one-pot synthesis of imine (N-benzylideneaniline) from benzyl alcohol and nitrobenzene was studied on the CdS–TiO2 photocatalyst under visible-light irradiation (λ > 420 nm) at 298 K. The photocatalytic activity strongly depends on the loadings of CdS on the TiO2, and the preferred amount of CdS was 15 wt%. Photo-electrochemical investigations were also incorporated to demonstrate the reaction mechanism: the CdS is photosensitized by visible-light irradiation, and an effective hole–electron separation is generated in the hetero-junction between the CdS and TiO2. It was also confirmed that the photocatalytic oxidation of benzyl alcohol proceeds over the CdS surface, while the hydrogenative reduction of nitrobenzene into aminobenzene proceeds over the TiO2 surface. Moreover, the production of imine proceeded efficiently by the successive condensation of benzaldehyde and aminobenzene on the catalyst surface under dark conditions.

Inorganic dye-sensitized solar cell employing In-enriched Cu–In–S ternary colloids prepared in water media

Copper–indium–sulfur (CIS) ternary colloids with different chemical compositions (In/Cu = 1, 2, 3 and 4) were synthesized in “green” water media at 298 K. It was observed that these CIS colloidal particles possess identical crystal structures in tetrahedron. They exhibit energy gaps at 1.7–2.0 eV, which is attributed to the quantum size effects through a decrease of particle sizes from 4 to 2 nm. It was also found that the photoelectrodes employing CIS colloids with the In-enriched compositions exhibit high incident photon to current efficiency (IPCE) up to ca. 780 nm. The solar cell constructed by CIS–TiO2||Sx2−/xS2−||carbon electrode exhibited a power conversion efficiency (PCE) up to ca. 2.5%. Furthermore, the CIS–TiO2 photoelectrode coated with ZnS as passivation layers by SILAR processes exhibited a remarkable improvement of the PCE up to 3.54% (short-circuit current: 8.72 mA cm−2, open-circuit voltage: 750 mV and fill factor: 53.6%). Effects of chemical compositions and ZnS coating to the photoelectrodes were further discussed by electrochemical impedance spectroscopy.

Investigation of the Local Structure of Vanadium Silicalite Catalyst (VS-1) Using XAFS, FT-IR and Photoluminescence Spectroscopic Methods

The in situ characterization of the vanadium silicalite catalyst (VS-1) was carried out using XAFS (XANES, EXAFS), FTIR and dynamic photoluminescence techniques. The FT-IR spectrum of the VS-1 catalyst at around 960 cm-1 showed the incorporation of vanadium atoms into the zeolite framework. Furthermore, XAFS measurements have indicated that the VS-1 catalyst consists of highly dispersed vanadium oxide species having a tetrahedral coordination. The VS-1 catalyst exhibited an absorption band at around 300 nm and an intense photoluminescence with a vibrational fine structure at around 450-550 nm which could be attributed to the charge transfer processes on the tetrahedral vanadium oxide species involving an electron transfer from O2- to V5+ and reverse radiative decay, respectively. These results have indicated that a highly dispersed vanadium oxide species is present within the zeolite framework as a tetrahedrally coordinated species and the charge transfer excited state of this oxide species can be well-localized in the shorter V=O bond.

Surface-Functionalized TiO2 Photocatalyst Modified by the Interfacial Surface Complex (ISC)

In this chapter, TiO2 photocatalyst modified with the interfacial surface complex (ISC), which exhibits selective oxidation of several aromatic alcohols under visible-light irradiation is reviewed. It was confirmed that benzylic alcohols with several substituted groups are converted into the corresponding benzaldehydes with high selectivity (>99 %). Furthermore, the origin of the visible-light response and the reaction mechanisms for the photocatalytic oxidation of benzylic alcohols were discussed by the combination of DFT calculations. Also, effects of substituted groups in the benzylic alcohols and their orientations on the photocatalytic activities were discussed.