Masaya Matsuoka

Understanding TiO2 Photocatalysis: Mechanisms and Materials

Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Photocatalytic decomposition of NO under visible light irradiation on the Cr-ion-implanted TiO2 thin film photocatalyst

Transparent TiO2 thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by the ionized cluster beam (ICB) method. In order to improve the photocatalytic performance of these thin films under visible light irradiation, transition metal ions such as Cr and V were implanted into the deep bulk inside of the films using an advanced metal‐ion‐implantation technique. The UV‐vis absorption spectra of these metal‐ion‐implanted TiO2 thin films were found to shift smoothly toward visible light regions, its extent depending on the amount and kinds of metal ions implanted. Using these metal‐ion‐implanted TiO2 thin films as photocatalysts, the photocatalytic decomposition of NOx into N2 and O2 was successfully carried out under visible light (λ 450 nm) irradiation at 275 K.

Local structures, excited states, and photocatalytic reactivities of highly dispersed catalysts constructed within zeolites

Abstract Transition metal oxides (Ti, V, Mo, Cr) incorporated within the framework of zeolites as well as transition metal ions (Cu+, Ag+, Pr3+) exchanged within the zeolite cavities were found to exhibit high and unique photocatalytic activities for various reactions such as the decomposition of NOx (NO, N2O) into N2 and O2 or the reduction of CO2 with H2O to produce CH4 and CH3OH. Various in situ spectroscopic investigations of these catalytic systems using photoluminescence, X-ray absorption fine structure (XAFS) (X-ray absorption near edge structure (XANES) and Fourier transform of EXAFS (FT-EXAFS)), electron spin resonance (ESR), FT-IR, etc. revealed that the photo-excited states of these transition metal oxides or ions play a vital role in these photocatalytic reactions. The photocatalytic reactivity of these oxides and ions in their efficiency and selectivity were found to depend strongly on their local structures, which are controlled by the unique and restricted framework structures of zeolites.

Efficient hydrogen production and photocatalytic reduction of nitrobenzene over a visible-light-responsive metal–organic framework photocatalyst

Efficient hydrogen production and photocatalytic reduction of nitrobenzene were achieved by using a Pt-deposited amino-functionalised Ti(IV) metal–organic framework (Pt/Ti-MOF-NH2) under visible-light irradiation. XRD and N2 adsorption measurements revealed that crystalline microporous structures were formed and maintained even after the Pt deposition. The photocatalytic activity for the visible-light-promoted hydrogen production was improved through the optimization of the deposition amount of Pt as a cocatalyst. The optimised amount of Pt was determined to be 1.5 wt%. The results of in situ ESR measurements clearly indicate that the reaction proceeds through the electron transfer from the organic linker to deposited Pt as a cocatalyst by way of titanium-oxo clusters. In addition, the Pt/Ti-MOF-NH2 photocatalyst was found to catalyse photocatalytic reduction of nitrobenzene under visible-light irradiation. It was also confirmed that the catalyst can be reused at least three times without significant loss of its catalytic activity.

Design of photocatalysts encapsulated within the zeolite framework and cavities for the decomposition of NO into N2 and O2 at normal temperature

Abstract The design of photocatalysts encapsulated within the zeolite frameworks and cavities is the most promising approach in developing photocatalysts which will operate efficiently and effectively towards the purification of toxic agents such as NO x and SO x in the atmosphere. In the present study, the vanadium silicalite (VS-2) and Ag + /ZSM-5 catalysts were prepared by hydrothermal synthesis and ion-exchange, respectively, and the in situ characterization of these catalysts and their photocatalytic reactivities for the decomposition of NO have been investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), ESR, FT—IR, LTV—VIS, solid-state NMR and XRD techniques along with an analysis of the reaction products. Results obtained with the VS-2 catalyst showed that vanadium oxide moieties are present within the zeolite framework as a 4-fold tetrahedrally coordinated vanadium oxide species having a terminal oxovanadium group (VO). UV irradiation of the VS-2 catalyst in the presence of NO led to the photocatalytic decomposition of NO to form N 2 , N 2 O and O 2 . On the other hand, it was found that the zeolite cavities can stabilize the Ag + ions in an isolated state through their connection with two lattice oxygen anions of the zeolite (2-coordination geometry). These isolated Ag + ions exhibit high photocatalytic reactivities for NO decomposition to form N 2 , N 2 O and NO 2 . Dynamic studies of the excited state of these catalysts showed that the charge transfer from the excited state of the vanadium oxide species or Ag + ions to NO plays a vital role in the initiation of the decomposition of NO into N and O. These findings have demonstrated that metal oxide species and metal ions included within the zeolite frameworks and cavities are strong candidates for new types of environmentally applicable photocatalysts.

Carbon dots modified mesoporous organosilica as an adsorbent for the removal of 2,4-dichlorophenol and heavy metal ions

Periodic mesoporous organosilica embedded with carbon dots are adopted as the adsorbent for removal of the toxic organic pollutant 2,4-dichlorophenol and inorganic metal ions Hg(II), Cu(II), and Pb(II). The composite possesses an ordered 2D hexagonal mesostructure with a space group of p6mm, high specific surface area (∼468.46 m2 g−1), and uniform pore size (∼5.50 nm). The surface is covered by about 1–2 layers of carbon dot nanoparticles. The maximum adsorption capacity for 2,4-dichlorophenol is 99.70 mg g−1, and the distribution coefficient of metal ions between adsorbent and solution phases is in the range of 2.60–7.41, following the order of Hg(II) > Cu(II) > Pb(II). The Cu(II) and Pb(II) adsorption stays nearly fixed while Hg(II) adsorption is depressed by ∼45% in a mixed solution of metal ions. The Cu(II) and Hg(II) adsorption shows unapparent variation but Pb(II) adsorption is improved by ∼55% in a mixed solution of metal ion and 2,4-dichlorophenol. In contrast, all metal ions lead to the depression of 2,4-dichlorophenol adsorption by 37% (Pb(II)), 45% (Cu(II)), and 48% (Hg(II)). Finally, the n–π electron donor–acceptor interaction between O- and N-containing groups in mesoporous organosilica and the benzene ring in 2,4-dichlorophenol is revealed to be responsible for the enhanced adsorption of 2,4-dichlorophenol, while the electrostatic force and complex formation between metal ions and amide groups co-contribute to the improvement of metal ions adsorption.

The photocatalytic decomposition of nitric oxide on Ag+/ZSM-5 catalyst prepared by ion-exchange

Abstract Over Ag+/ZSM-5 catalyst prepared by an ion-exchange the photocatalytic decomposition of NO into N2, N2O, and NO2 was affected by UV irradiation at a low temperature of 298 K. In situ X-ray absorption near edge structure (XANES), ESR, photoluminescence, and diffuse reflectance (DR) spectroscopy were applied to examine the Ag+/ZSM-5 catalyst. The wavelengths of the effective UV irradiation was determined. Data suggest that electron transfer from excited Ag+ ion into the π anti-bonding molecular orbital of NO molecule plays a significant role in the photocatalytic decomposition of NO.

Photocatalytic decomposition of NO on titanium oxide thin film photocatalysts prepared by an ionized cluster beam technique

Transparent TiO2 thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by an ionized cluster beam (ICB) method. The UV‐VIS absorption spectra of these films show specific interference fringes, indicating that uniform and transparent TiO2 thin films are formed. The results of XRD measurements indicate that these TiO2 thin films consist of both anatase and rutile structures. UV light (λ > 270 nm) irradiation of these TiO2 thin films in the presence of NO led to the photocatalytic decomposition of NO into N2, O2 and N2O. The reactivity of these TiO2 thin films for the photocatalytic decomposition of NO is strongly dependent on the film thickness, i.e., the thinner the TiO2 thin films, the higher the reactivity.

Application of an amino-functionalised metal–organic framework: an approach to a one-pot acid–base reaction

The amino-functionalised metal–organic framework, MIL-101(Al)-NH2, has been synthesized by using a solvothermal method and employed as a bifunctional acid–base catalyst for a one-pot, sequential deacetalization–Knoevenagel condensation reaction. In preliminary studies, the abilities of MIL-101(Al)-NH2 to serve as an acid and base catalyst were explored separately by two typical acid- and base-catalysed reaction, that is, deacetalization of benzaldehyde dimethylacetal and Knoevenagel condensation of benzaldehyde with malononitrile. MIL-101(Al)-NH2 was found to catalyse each of these reactions with high efficiency. MIL-101(Al)-NH2 was then employed as a catalyst for the one-pot sequential deacetalization–Knoevenagel condensation reaction between benzaldehyde dimethylacetal and malononitrile. Benzylidenemalononitrile as the final product was successfully generated with a high yield via benzaldehyde over MIL-101(Al)-NH2. In addition, the catalytic ability of MIL-101(Al)-NH2 was demonstrated to be superior to those of conventional heterogeneous, homogeneous as well as other functionalised metal–organic framework catalysts. Finally, the results show that MIL-101(Al)-NH2 can be reused as a catalyst for this process without significant loss of its activity.

In situ investigations of the photocatalytic decomposition of NOx on ion-exchanged silver(I) ZSM-5 catalysts

Abstract Ag+/ZSM-5 catalyst was prepared by an ion-exchange method. In situ EXAFS, ESR, photoluminescence, and diffuse reflectance (DR) spectroscopy were applied to characterize the Ag+/ZSM-5 catalyst. UV irradiation of the Ag+/ZSM-5 catalyst in the presence of NO led to the photocatalytic conversion of NO into N2, N2O and NO2 at temperatures as low as 298 K. The wavelengths of the effective UV irradiation were determined. The results obtained in this study suggest that electron transfer from excited Ag+ ion into the π anti-bonding molecular orbital of NO plays a significant role in the photocatalytic decomposition of NO.