Search

Mesoporous silica nanospheres with an average diameter of approximately 240 and 600 nm have been used as catalyst supports of active Pt nanoparticles, which were found to be highly efficient for liquid-phase hydrogenation under atmospheric H compared to the micron-sized conventional mesoporous silica because of the suppression of mass-transport limitation toward active sites. [ABSTRACT FROM AUTHOR]

In the past decades, various photocatalysts such as TiO2, transition-metal-oxide moieties within cavities and frameworks, or metal complexes have attracted considerable attention in light-excited catalytic processes. Owing to high surface areas, transparency to UV and visible light as well as easily modified surfaces, mesoporous silica-based materials have been widely used as excellent hosts for designing efficient photocatalytic systems under the background of environmental remediation and solar-energy utilization. This Minireview mainly focuses on the surface-chemistry engineering of TiO2/mesoporous silica photocatalytic systems and fabrication of binary oxides and nanocatalysts in mesoporous single-site-photocatalyst frameworks. Recently, metallic nanostructures with localized surface plasmon resonance (LSPR) have been widely studied in catalytic applications harvesting light irradiation. Accordingly, silver and gold nanostructures confined in mesoporous silica and their corresponding catalytic activity enhanced by the LSPR effect will be introduced. In addition, the integration of metal complexes within mesoporous silica materials for the construction of functional inorganic-organic supramolecular photocatalysts will be briefly described. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) of various colors were synthesized within the mesopore structure of SBA‐15 by using microwave‐assisted alcohol reduction. The charge density is partially localized on the surface of these Ag NPs owing to localized surface plasmon resonance. This charge localization results in them having enhanced catalytic activity under visible light irradiation compared to Ag NPs obtained by thermal processes. [ABSTRACT FROM AUTHOR]

[Pt(tpy)Cl]Cl (tpy: terpyridine) was successfully anchored to a series of mesoporous-silica materials that were modified with (3-aminopropyl)triethoxysilane with the aim of developing new inorganic-organic hybrid photocatalysts. Herein, the relationship between the luminescence characteristics and photocatalytic activities of these materials is examined as a function of Pt loading to define the spatial distribution of the Pt complex in the mesoporous channel. At low Pt loading, the Pt complex is located as an isolated species and exhibits strong photoluminescence emission at room temperature owing to metal-to-ligand charge-transfer (3MLCT) transitions (at about 530 nm). Energy- and/or electron-transfer from 3MLCT to O2 generate potentially active oxygen species, which are capable of promoting the selective photooxidation of styrene derivatives. On the other hand, short Pt⋅⋅⋅Pt interactions are prominent at high loading and the metal-metal-to-ligand charge-transfer (3MMLCT) transition is at about 620 nm. Such Pt complexes, which are situated close to each other, efficiently catalyze H2-evolution reactions in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light irradiation. This study also investigates the effect of nanoconfinement on anchored guest complexes by considering the differences between the pore dimensions and structures of mesoporous-silica materials. [ABSTRACT FROM AUTHOR]

Using microwave-assisted deposition method the uniform and nano-sized platinum metal particles were prepared on the tetrahedrally coordinated Ti-oxide moieties isolated within the framework of mesoporous silica supports. The present nano-sized metal catalyst exhibited a higher activity for hydrogenation of nitrobenzene than the catalyst prepared by a conventional impregnation method. [ABSTRACT FROM AUTHOR]

A facile and unique methodology to synthesize the nano-sized and uniform noble metal (Pt and Au) particles has been developed using mesoporous silica support including single-site titanium oxide moieties (Ti-HMS) under microwave irradiation. Characterization by CO adsorption, XAFS, and TEM analysis revealed that the size of metal particles depends on the preparation methods and that the smaller sizes of metal particles were formed on the microwave-assisted metal catalysts compared to the conventionally prepared impregnated catalysts. These nano-sized metal catalysts are useful as efficient catalysts for the various reactions such as the hydrogenation of nitrobenzene and oxidation of CO. This method is also successfully applicable to the deposition of Au metal with smaller size on the Ti-HMS. [ABSTRACT FROM AUTHOR]

The influence of transition metals, such as Ag, Cr, and Co, on the photocatalytic properties of titania-silica (TiO2-SiO2) prepared via both impregnation (imp) and photo-assisted deposition (PAD) methods has been investigated. The decomposition of 2-propanol under UV-light irradiation was used to probe the effect of transition metals deposition on the activity of titania-silica. PAD-Ag/TiO2-SiO2 prepared by the PAD method was highly active compared to the original TiO2-SiO2, while imp-Cr/TiO2-SiO2 prepared by conventional impregnation method showed a weak tendency toward the decomposition of 2-propanol. [ABSTRACT FROM AUTHOR]

Steel slag, commercial waste material containing silica and alumina which are the chemical components elements of zeolite, was used as a source for synthesis of FAU zeolite (Y-zeolite, X-zeolite). Through acid-treatment to remove CaO species from steel slag and hydrothermal treatment, well-crystallized Na type FAU zeolite was obtained. Furthermore the synthesized FAU zeolite was applied as a support of photocatalyst. It was found that hydrophobic surface property of zeolite enhances photocatalytic activity for decomposition of organic pollutants and the zeolite synthesized from steel slag would be applicable as promising support of TiO2 photocatalyst. [ABSTRACT FROM AUTHOR]

Abstract: Using a sol–gel/spin coating method, the transparent metal(Ti,Cr)-containing mesoporous silica thin films could be prepared on quarts plates. In the case of the Ti-containing mesoporous silica (TMS) thin film, the formation of isolated and tetrahedrally-coordinated Ti oxide species in the frameworks was confirmed by XRD, UV–vis, and Ti K-edge XAFS measurements. The TMS thin film has been proved to exhibit a strong hydrophilic property even before UV irradiation compared to the common mesoporous silica and TiO2 thin films. After UV-light irradiation, the contact angle of water droplet on the TMS thin film become extremely lower, indicating the appearance of the photo-induced super-hydrophilic property. We have also synthesized the transparent Cr-containing mesoporous silica (CMS) thin film containing tetrahedrally-coordinated Cr oxide species, which showed the super-hydrophilic property even under visible light irradiation. By using the polymerization ability of the isolated Cr oxide species under UV light irradiation, the polyethylene phase was successfully formed on the surface of the CMS thin film. It was demonstrated that the surface property of the CMS was converted into hydrophobic while keeping its transparency. The single-site Cr oxide moieties are responsible for the photo-induced surface reaction as well as controlling the surface hydrophilic–hydrophobic properties. [Copyright &y& Elsevier]

The tetrahedrally coordinated metal oxide (titanium, vanadium, chromium, and molybdenum oxides) moieties can be implanted and isolated in the silica matrixes of microporous zeolite and mesoporous silica materials and named as "single-site photocatalysts." Under UV-light irradiation these single-site photocatalysts form the charge-transfer excited state, i.e., the excited electron-hole pair state which localizes quite near to each other as compared to the electron and hole produced in semiconducting materials, plays a significant role in various photocatalytic reactions. Especially, the single-site titanium oxide photocatalyst demonstrates the high reactivity and selectivity under UV-light irradiation, while the single-site chromium oxide operates as a visible-light sensitive photocatalyst. These single-site photocatalysts not only can promote photocatalytic reactions but also can be utilized to synthesis of functional materials. The transparent mesoporous thin film with single-site photocatalyst generates the superhydrophilic surface. The nano-sized metal catalyst can be photodeposited on the excited single-site photocatalyst under UV-light irradiation. [ABSTRACT FROM AUTHOR]

The Front Cover image shows various photocatalysts such as nano‐sized TiO2, transition‐metal‐oxide moieties (single‐site photocatalysts), plasmonic metal nanostructures, and metal complexes displaying various light‐excited photocatalytic processes. All of the processes occur in the nanospace of mesoporous silica‐based materials, which possess high surface areas, transparency to UV and visible light as well as easily modified surfaces. More details can be found in the Minireview by Yamashita et al. on page 1528 (DOI: 10.1002/cssc.201400111), while more information about the research group is available in the Cover Profile (DOI: 10.1002/cssc.201400098). [ABSTRACT FROM AUTHOR]

Magnetic iron oxide nanoparticles coated with mesoporous silica involving single-site titanium oxide moiety have been first developed by adopting a two-step coating method. The catalytic performance and magnetically separable ability were demonstrated in the oxidation of 2,6-di-tert-butylphenol using hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Using a sol- gel/spin-coating method, transparent mesoporous silica thin films containing single-site photocatalyst (Ti, V, Cr, Mo, and W oxide moieties) (Me-MSTFs) could be prepared on quartz plates. All Me-MSTFs have exhibited strong hydrophilic surface properties even before UV-light irradiation and showed photoinduced superhydrophilic properties after UV-light irradiation. Among examined samples, the W-MSTF showed the highest hydrophilicity. [ABSTRACT FROM AUTHOR]

Abstract: A simple methodology to synthesize uniform and nano-sized Pd particles supported on silica support has been developed by the electroless deposition technique using Sn2+ ion, in which Pd precursor can be interacted directly with the Sn2+ ion, and subsequently transformed into Pd nanoparticles. Characterization by TEM analysis proved that the sizes of the Pd nanoparticles using the electroless deposition technique (eld-Pd/SiO2(Sn)) were quite uniform with smaller size compared with that prepared by the conventional impregnation method (imp-Pd/SiO2). Their catalytic applications for the hydrogenation of nitrobenzene and the direct synthesis of H2O2 from H2 and O2 gases were investigated and it is demonstrated that eld-Pd/SiO2(Sn) prepared by the electroless deposition technique was shown to perform significantly better activity than the imp-Pd/SiO2 owing to its uniform and nano-sized Pd particles. [Copyright &y& Elsevier]

Abstract: Hydrophobic modification of single-site Ti-oxide moieties containing mesoporous silica (TiSBA-15) surfaces was performed by using triethoxyfluorosilane (TEFS) as a silylation reagent. The pore structure as well as the high surface area of TiSBA-15 was retained even after modification of these surfaces. TiSBA-15 modified with suitable amount of TEFS exhibited higher catalytic performance for the selective oxidation of cyclooctene to 1,2-epoxy cyclooctane using aqueous H2O2 as an oxidant than the unmodified TiSBA-15. The improvement of surface hydrophilic–hydrophobic properties of TiSBA-15 is quite effective for the enhancement of catalytic activity. [Copyright &y& Elsevier]

Abstract: Ti-containing mesoporous silica thin films (Ti-MSTFs) have been prepared on Al and Al–Mg alloy substrates via a sol–gel/spin-coating method including two different processes for removal of a structure directing agent (SDA). One is calcination and the other is photocatalytic removal under UV-light irradiation utilizing photocatalysis of tetrahedrally coordinated titanium oxide moieties within the silica framework. Characterizations of mesoporous structures and local structures of titanium oxide moieties were performed by FT-IR, XRD, and UV–vis measurements. Water contact angle measurements revealed that highly hydrophilic surfaces were successfully formed on both metallic substrates by coating with Ti-MSTFs. These surfaces also exhibited photoinduced superhydrophilic properties under UV-light irradiation. [ABSTRACT FROM AUTHOR]

Review: 96 refs. [ABSTRACT FROM AUTHOR]