Takashi Kamegawa

Design and functionalization of photocatalytic systems within mesoporous silica.

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.

Enhanced photocatalytic properties of TiO2-loaded porous silica with hierarchical macroporous and mesoporous architectures in water purification

Porous silica with hierarchical macroporous and mesoporous architectures (MacroMeso-SiO2) was prepared by a solvent evaporation method using a precursor solution for the synthesis of mesoporous silica (Meso-SiO2) and poly(methyl methacrylate) (PMMA) colloidal crystals as a hard template and used as an advanced support for TiO2 photocatalysts. The porous structure and state of TiO2 were investigated by various characterisation techniques. Reflecting the structure of aligned PMMA microspheres, MacroMeso-SiO2 has a uniform and hierarchical macroporous structure with interconnecting networks even after the loading of TiO2 particles. Based on its advantageous porous structure, TiO2-loaded MacroMeso-SiO2 exhibited specific characteristics, i.e., the easy transportation of relatively large molecules and unique adsorption properties to condense organic compounds, and enhanced photocatalytic properties in the degradation of organic compounds in water as compared to TiO2-loaded Meso-SiO2 under UV light irradiation.

Synthesis of highly visible light active TiO2-2-naphthol surface complex and its application in photocatalytic chromium(VI) reduction

Photocatalysis is an effective approach for the removal of heavy metal ions present in the aquatic bodies. In this report, TiO2 nanoparticles were successfully functionalized with 2-naphthol (2-NAP) using simple and scalable condensation reaction. The prepared photocatalyst was demonstrated as superior visible light photocatalyst for the effective reduction of Cr(VI). The 2-NAP functionalized TiO2 displayed a remarkable enhancement in the photocatalytic reduction of Cr(VI) under visible light irradiation (λ > 400 nm). The maximum Cr(VI) reduction of about 100% (7 fold higher activity than bare TiO2) was achieved within 3 h. The discernible enhancement in the photocatalytic reduction of TiO2-2-NAP can be ascribed to improved optical absorption in visible region, high crystallinity of TiO2 and high surface area. In addition, the photogenerated electron transfer from 2-NAP to TiO2 (ligand to metal transfer) can significantly improved the photocatalytic performance than bare TiO2 counterparts. Therefore, the functionalization of metal oxides with organic ligands can open new directions to overcome the existing limitations in photocatalysis.

Hydrophobic Modification of Pd/SiO2@Single‐Site Mesoporous Silicas by Triethoxyfluorosilane: Enhanced Catalytic Activity and Selectivity for One‐Pot Oxidation

To enhance the catalytic activity in a selective one-pot oxidation using in-situ generated H(2)O(2), a hydrophobically modified core-shell catalyst was synthesized by means of a simple silylation reaction using the fluorine-containing silylation agent triethoxyfluorosilane (TEFS, SiF(OEt)(3)). The catalyst consisted of a Pd-supported silica nanosphere and a mesoporous silica shell containing isolated Ti(IV) and F ions bonded with silicon (SiF bond). Structural analyses using XRD and N(2) adsorption-desorption suggested that the mesoporous structure and large surface area of the mesoporous shells were retained even after the modification. During the one-pot oxidation of sulfide, catalytic activity was enhanced significantly by increasing the amount of fluorine in the shell. A hydrophobic surface enhanced adsorption of the hydrophobic reactant into the mesopore, while the less hydrophobic oxygenated products efficiently diffused into the outside of the shell, which improved the catalytic activity and selectivity. In addition, the present methodology can be used to enhance the catalytic activity and selectivity in the one-pot oxidation of cyclohexane by using an Fe-based core-shell catalytic system.

Photocatalytic Properties of TiO2-Loaded Porous Silica with Hierarchical Macroporous and Mesoporous Architectures

In this chapter, application of porous siliceous materials as platforms for design of TiO2-based photocatalysts is reviewed. Porous siliceous materials with one or both types of pores, i.e., ordered mesopores and hierarchical macropores, were synthesized by applying template strategies. Based on the advantageous porous structure, TiO2-loaded porous silica with hierarchical macroporous and mesoporous architectures exhibited specific characteristics (e.g., an easy transportation of relatively large molecules and unique adsorption properties to condense organic compounds), and enhanced photocatalytic properties in the degradation of organic compounds in water under UV light irradiation.