Keita Ikeue

The design and development of second-generation titanium oxide photocatalysts able to operate under visible light irradiation by applying a metal ion-implantation method

Unique second-generation titanium oxide photocatalysts enabling effective and efficient reactions not only under ultraviolet (UV) but also visible light irradiation have been successfully designed and developed by applying a metal ion-implantation method. With these second-generation titanium oxide photocatalysts, solar beams are absorbed up to 25-30% more efficiently, allowing their large scale use for the reduction of enviromental toxins.

In situ XAFS Studies on the Effects of the Hydrophobic–Hydrophilic Properties of Ti-Beta Zeolites in the Photocatalytic Reduction of CO2 with H2O

The photocatalytic reduction of CO2 with H2O to produce CH4 and CH3OH was found to proceed in the gas phase at 323 K with different reactivities and selectivities on hydrophilic Ti-Beta(OH) and hydrophobic Ti-Beta(F) zeolites prepared in the OH− and F− media, respectively. In situ XAFS measurements have revealed that these differences are attributed to the differences in the affinity for the adsorption of H2O molecules on the highly dispersed tetrahedrally coordinated titanium oxide species depending on the hydrophobic–hydrophilic properties of zeolites.

Photocatalytic reduction of CO2 with H2O on Ti-containing porous silica thin film photocatalysts

Two different Ti-containing porous silica thin films having a hexagonal and cubic pore structure were synthesized and used as photocatalysts for the reduction of CO2 with H2O at 323 K. UV irradiation of the Ti-containing porous silica thin films in the presence of CO2 and H2O led to the formation of CH4 and CH3OH with a high quantum yield of 0.28%. These porous silica thin film photocatalysts having a hexagonal pore structure exhibited higher reactivity than the Ti-MCM-41 powder photocatalysts with the same pore structure.

Characterization and photocatalytic reduction of CO2 with H2O on Ti/FSM-16 synthesized by various preparation methods

Ti/FSM-16 photocatalysts were prepared by various methods and their reactivity for the photocatalytic reduction of CO2 with H2O at 323 K was investigated. UV irradiation of Ti/FSM-16 in the presence of CO2 and H2O led to the formation of CH4 and CH3OH. The photocatalytic reactivity and selectivity differed remarkably by variations in the preparation method. Analyses of the UV-Vis absorption and XAFS spectra showed that the dispersion and local structure of the Ti-oxide species greatly depended on the preparation method. The formation of CH3OH was found to be related to the local structure of the Ti-oxide species while the yield of the photoluminescence was attributed to the charge transfer excited state of the highly dispersed tetrahedrally coordinated Ti-oxide species. Methanol formation was found to be more efficient on Ti/FSM-16 having such highly dispersed tetrahedrally coordinated Ti-oxide species.

Photocatalytic reduction of CO2 with H2O on titanium oxides anchored within zeolites

Titanium oxide species anchored within the zeolite cavities and framework by an ion-exchange method and a hydrothermal synthesis exhibit high and unique photocatalytic reactivity for the reduction of CO 2 with H 2 O at 328 K with a high selectivity for the formation of CH 3 OH in the gas phase. In situ photoluminescence, ESR, diffuse reflectance absorption and XAFS investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species plays a significant role in the reduction of CO 2 with H 2 O exhibiting a high selectivity for the formation of CH 3 OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH 4 .

Characterization of Ti-Beta zeolites and their reactivity for the photocatalytic reduction of CO2 with H2O

A characterization of Ti-Beta zeolites synthesized under various conditions as well as an investigation of their photocatalytic properties for the reduction of CO2 with H2O at 323 K to produce CH4 and CH3OH were carried out. In situ XAFS spectra measurements indicated that a highly dispersed tetrahedral titanium oxide species was present in the zeolite framework and an increase in the coordination number of the titanium oxide species by the addition of H2O and CO2 molecules could be detected. The Ti-Beta zeolite having a hydrophilic property (Ti-Beta(OH)) exhibited a more dramatic increase in the coordination number than the Ti-Beta(F) zeolite which had a hydrophobic property. These results suggest that CO2 and H2O molecules can be adsorbed efficiently onto the highly dispersed tetrahedrally coordinated titanium oxide species. UV irradiation of these Ti-Beta zeolite catalysts in the presence of H2O and CO2 led to the formation of CH4 and CH3OH. Ti-Beta(OH) exhibited a higher reactivity than Ti-Beta(F), while the selectivity for the formation of CH3OH on Ti-Beta(F) was higher than that for Ti-Beta(OH). These results indicated that the reactivity and selectivity of the zeolite catalyst can be determined by the hydrophilic and hydrophobic properties of the zeolites.

Photocatalytic epoxidation of propene with molecular oxygen under visible light irradiation on V ion-implanted Ti-HMS and Cr-HMS mesoporous molecular sieves

Abstract The metal ion-implantation with V ions was effective to shift the absorption band of Ti- containing mesoporous molecular sieves (V/Ti-HMS, V/Ti-MCM-41 ) to the longer wavelengths. V/Ti-HMS and V/Ti-MCM-41 performed the photoepoxidation of propene with molecular oxygen under UV irradiation with the longer wavelength (λ> 340 nm), while no reaction proceeded on the original Ti-HMS. Cr-containing mesoporous molecular sieves (Cr- HMS) could absorb visible light and showed the photoepoxidation under visible light irradiation ( λ> 450 nm). The charge transfer excited state of the tetrahedral chromium oxide moieties dispersed on mesoporous silica played a significant role in the photocatalytic reaction.

Effect of H2O affinity of Ti-BETA zeolite on adsorption property and photocatalytic reactivity for degradation of 2-propanol diluted in water

The liquid-phase photocatalytic degradation of 2-propanol diluted in water to produce CO2 and H2O was found to proceed more efficiently on the hydrophobic Ti-Beta(F) zeolite than on hydrophilic TiBeta(OH) zolite prepared in the F− and OH− media, respectively. Chemical adsorption measurements have revealed that efficient photocatalytic degradation of 2-propanol diluted in water on Ti-Beta(F) zeolite can be attributed to the larger affinity for the adsorption of propanol molecules on the titanium oxide species depending on the hydrophobic surface properties of this photocatalyst.