M. Anpo

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.

Photocatalytic decomposition of liquid-water on the Pt-loaded TiO2 catalysts: Effects of the oxidation states of Pt species on the photocatalytic reactivity and the rate of the back reaction

The photocatalytic decomposition of liquid water on Pt-loaded TiO2 (Pt/TiO2) catalysts was investigated. The results obtained by XPS and XRD measurements of the catalysts as a function of the calcination temperature as well as the photocatalytic decomposition reactions of H2O clearly indicate that controlling the oxidation state of Pt as well as the amount of loaded Pt species are both important factors in the design of water-splitting photocatalysts having high efficiency and stoichiometry.

Study on the formation of H2O2 on TiO2 photocatalysts and their activity for the photocatalytic degradation of X-GL dye

Titanium dioxide (TiO2) nanoparticles of both anatase and rutile phases were synthesized by hydrothermal treatment of microemulsions, and their photocatalytic activity for the degradation of X-GL dye was investigated. The only difference between the two methods used was that different acids were added to the microemulsions to make a direct comparison of the photocatalytic activity of the polymorphs possible. UV — Vis reflectance and XRD spectroscopic investigations of these titanium dioxides indicated that a rutile structure could be formed (PR) when hydrochloric acid was used, and anatase formed (PA) when nitric acid was used. The activity of the two polymorphs and P-25 for the photocatalytic degradation of dye in water was also examined. It was found that P-25 consisting of anatase and rutile has the highest activity, and PR consisting of rutile has the lowest. Photodegradation of X-GL in the presence of these different TiO2 particles under air-equilibrated controlled conditions led to the formation of hydrogen peroxide. The formation rate of H2O2 depended on the difference in crystalloid phase. These results indicate that the observed differences in the photocatalytic activity for the three TiO2 photocatalysts are directly related to the formation rate of H2O2.

Characterization of the VS-1 catalyst using various spectroscopic techniques and its unique photocatalytic reactivity for the decomposition of NO in the absence and presence of C3H8

Abstract A Vanadium silicalite (VS-1) catalyst was prepared by hydrothermal synthesis. In situ characterizations were carried out and the photocatalytic reactivity of VS-1 were investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), UV–Vis and FT-IR techniques, along with an analysis of the reaction products. It was found that VS-1 involves a highly dispersed tetrahedrally coordinated V-oxide species having a VO bond within the zeolite framework. VS-1 exhibits photocatalytic reactivity for the decomposition of NO under UV irradiation, leading to the formation of N 2 , O 2 , N 2 O and NO 2 . The photocatalytic reaction of NO was dramatically enhanced in the presence of propane, leading to the formation of N 2 , propylene, and oxygen-containing compounds such as CH 3 COCH 3 and CO 2 , etc. with a good stoichiometry. The photocatalytic reactivity of VS-1 was found to be much higher than that of V/SiO 2 . The efficiency of the dynamic quenching of the photoluminescence of the V-oxide species in the excited state of VS-1 by small molecules such as NO or propane was found to be larger than that of V/SiO 2 . These results indicate that the high reactivity of the charge transfer excited triplet state of the V–O moieties, (V 4+ –O − ) * , of the VS-1 catalyst plays a significant role in the higher photocatalytic performance as compared with the V/SiO 2 catalyst.

Intrinsic band gap in semiconductor oxides and Ti-silicalite: ab initio and DFT study

Here we present the results of ab initio and DFT calculations mimicking the effect of transition metal ions on electronic and structural properties of Ti-silicalite, as well as of Na and N on rutile structures. The main discussion focuses on the excitation shifts into the longer wavelength region and their relation to the frontier orbitals that are expected to be responsible for the observed band gap changes. The results obtained allow us to give some insight in understanding the target phenomenon, as well as to point out on the importance of boundary frontier orbitals. These and other related findings are presented.

Local structure of highly dispersed lead containing zeolite. An ab initio and density functional theory study

Abstract Ab initio quantum chemical studies at the HF/Lanl2dz, B3PW91/Lanl2dz and B3LYP/Lanl2dz levels were carried out to investigate the local structures of the Pb 2+ active site of lead containing zeolites. It was shown that the coordination number which equals three is found to be the most favorable one for the Pb 2+ site within the zeolite lattice. The latter arises from the ground electronic state for the Pb 2+ within the zeolite lattice that involves lone pair of electrons at the 6s-AO. Thus, the Pb 2+ site would be in a strongly distorted tetrahedral environment. Due to the presence of the above lone pair of electrons, the adsorbate molecules would experience the repulsion from these electrons. The latter may explain some differences observed for the decomposition of pollutant molecules over the Cu + as well as Ag + ion-exchanged zeolites and the Pb 2+ ion-exchanged ones.

In-situ investigations of the photocatalytic reaction of no with propane on the vanadium silicalite-1 catalyst

The in-situ characterization of the vanadium silicalite-1 catalyst (VS-1) by means of photoluminescence, ESR and XAFS investigative techniques revealed that this catalyst includes highly dispersed V-O moieties having a tetrahedral coordination in C3v symmetry with one short V=O bond (1.63Å) and three long V-O bonds (1.73Å). The photocatalytic decomposition reaction of NO into N2 was found to proceed much more efficiently in the presence of propane than without. A dynamic quenching study of the photoluminescence spectrum of the VS-1 catalyst by the addition of NO and propane indicates that the excited state of the V-O moieties plays a significant role in this photocatalytic reaction.

Photophysical and photochemical processes in zeolite cavities: The effects of ion-exchanged alkalimetal cations on the excited states of xanthone and the photolysis of 2-pentanone

The characteristics properties of xanthone phosphorescence and of 2-pentanone photolysis in alkali metal cation-exchanged zeolites have been investigated to clarify the effect of the micro-environment of host-adsorbents on the photophysical and photochemical properties of guest-molecules in restricted void spaces. The enhancement of the phosphorescence yields of xanthone included in zeolites is observed by changing the exchangeablealkali metal cation from Li+ to Cs+. Simultaneously, the phosphorescence lifetimes were observed to continuously shorten by changing the cation from Li+ to Cs+. These results suggest that the external heavy-atom effect deriving from the alkali metal cations on the singlet-triplet transitions of xanthone molecules stabilized on alkali metal cations in the order of Li+, Na+, K+, Rb+, and Cs+. The yields for the photolysis of 2-pentanone included in zeolites increase with changing the alkali metal cation from Li+ to Cs+. IR investigations of the adsorption state of 2-pentanone indicate that strength of the interaction between the alkali metal cations and 2-pentanones decreases by changing the cation from Li+ to Cs+, which results in a longer lifetime of 2-pentanone. The selectivity of propylene formation is dramatically increased by changing the cation from Li+ to Cs+. The enhanced formation of propylene is asociated with the hydrogen absorption from propyl radicals by lattice oxygen, their basicity increasing by changing the cation from Li+ to Cs+. Thus, these changes in the zeolite cavities modified by exchanging cations caused significant effects not only on the excited state but also on the following chemical reactions of ketones.

Phosphorescence and photochemical properties of benzophenone included within alkali metal cation-exchanged ZSM-5 zeolites

The phosphorescence properties of benzophenone included within alkali metal cationexchanged ZSM-5 zeolites were investigated to clarify the effects of the micro-environment of hostadsorbents on the electronic excited states of guest-molecules included within the restricted void spaces. Benzophenone included within such cation-exchanged ZSM-5 zeolites was found to exist in both a protonated and hydrogen-bonded form. It was found that exchanging the cations dramatically affects the ratio of their contents. Photolysis of these systems revealed that both benzhydrol and benzpinacol were the main products, their yields strongly depending on the kind of the cations exchanged. Especially, the protonated species was found to play a significant role in the photoreactions observed with benzophenone included within zeolite cavities.

Effect of HF treatment on the activity of TiO2 thin films for photocatalytic water splitting

The effects of HF treatment on the activity of TiO2 thin films for the photocatalytic water splitting reaction have been investigated. TiO2 thin films treated with HF solution (HF-TiO2) were found to exhibit a remarkable enhancement of the photocatalytic activity for H2 evolution from a methanol aqueous solution, as well as efficient photoelectrochemical performance under UV light irradiation as compared with the untreated TiO2. Moreover, Pt-loaded HF-TiO2 thin films were found to act as efficient and stable photocatalysts for the decomposition of water under UV light irradiation. The mechanistic insights obtained in the present study will be useful in the design of highly efficient photocatalysts for the decomposition of water.