Tetsuya Shichi

Clay minerals as photochemical reaction fields

This article surveys the intercalation characteristics of a number of clay minerals which can be utilized as host materials for photofunctional organic–inorganic hybrid systems as well as photochemical anisotropic reaction fields. The introduction of this review describes the chemical compositions and the structural features of various kinds of artificial as well as naturally produced clays. The chemical structures of these clays are often considered to be complicated due to their unfamiliar names which are sometimes taken from the areas where they originate although, structurally, only slight differences actually exist. The second chapter summarizes the adsorption and aggregation properties of typical organic dyes in clays. The aggregation behavior is sensitive to the kind and amount of metallic ions present in the lattice of the clays, the amount of adsorbed water as well as the structure of the organic guests to be intercalated. All of these factors are discussed in relation to the adsorption and aggregation behavior. In the third chapter, the photochemical reactions of excited metal complexes adsorbed in clays are discussed. Electron transfers for [Ru(bpy)3]2+ in clays are described, showing that the clay layers provide reaction fields which stabilize the resulting charge separated species. This article aims to provide important insights into the fundamental mechanisms and properties of anisotropic reaction fields for the applications in design of promising, new photochemical and photobiological systems and processes.

Oxidation catalysis of a manganese(III)porphyrin intercalated in layered double hydroxide clays

Abstract Tetra( p -sulfonatophenyl)porphinatomanganese(III) anions, [Mn(III)TSPPCl] 4− were intercalated into the interlayer spaces of Mg–Al-layered double hydroxide (LDH) and studied as a catalyst for the oxidation of 2,4,6-trichlorophenol (TCP). The Mn(III)TSPP anions could be efficiently intercalated into the LDH interlayers as a perpendicular Mn(III)TSPP/LDH complex by adsorbing the guest molecules, which is a characteristic for easy handling and a high catalytic activity.

PET-clay hybrids with improved tensile strength

The hybridization of poly(ethylene terephthalate) (PET) with montmorillonite (Mont) was investigated by using hydroxypentyltrimethylammonium iodide (HPTA) as an ionic anchor monomer capable of being adsorbed onto clay surfaces by ion exchange. The HPTA/Mont hybrid films copolymerized with bis (hydroxyethyl) terephthalate (BHET) exhibited favorable characteristics such as improved tensile strength as well as optical transparency.

Photocatalytic Activity of NaNbO3 Thin Films

NaNbO(3) thin films prepared by the sol-gel method had homogeneous microstructure with an average grain size of 15-25 nm and exhibited photoinduced hydrophilic conversion under UV irradiation. However, the films had little photocatalytic oxidation activity under UV irradiation. This is the first observation that NaNbO(3) undergoes photoinduced hydrophilicity under UV irradiation.

Preparation and characterization of self-cleaning glass for vehicle with niobia nanosheets.

Self-cleaning glasses were prepared by coating niobia nanosheets and investigated on the performance. The coated glass heated at >450 degrees C had very low turbidity, high hardness, and excellent adhesion properties. Niobia nanosheets ([Nb(3)O(8)](-)) reacted with sodium ions (Na(+)) diffused from the glass into the films to form a crystalline phase of NaNb(3)O(8) and this phase was converted to NaNbO(3) at >450 degrees C. The films exhibited photoinduced hydrophilicity under UV irradiation but low photocatalytic oxidation activity. Excellent self-cleaning ability of the niobia nanosheet coated glass was confirmed by the Taber abrasion test, which is thought to be a candidate as self-cleaning glasses for vehicles.

Photochromism in Oriented Thin Films Prepared by the Hybridization of Diarylethenes in Clay Interlayers

Abstract The photochromism of 1,2-bis(2-methyl-3-thiophenyl)perfluorocyclo-pentene bearing two pyridinium substituents at each thiophenyl ring (1) in smectite clay thin films is the subject of the present study. In order to prepare oriented thin films with photochromic characteristics, the hybridization of cationic diarylethene molecules, 1, into the layered clay was carried out, and the structure and photochromic properties of these hybrid materials were investigated. Clay intercalated diarylethene exhibited typical photochromic behavior. Polarized spectroscopic data has confirmed the diarylethenes inside the clay to be present as a tilted monolayer. Although the photochromic efficiency of these hybrid materials gradually decreased upon repeated irradiation with alternative UV and visible light, photochromic degradation could be dramatically improved by the cointercalation of cationic surfactant molecules such as dodecylpyridinium ions.

Fabrication of vertically aligned diamond whiskers from highly boron-doped diamond by oxygen plasma etching.

Conductive diamond whiskers were fabricated by maskless oxygen plasma etching on highly boron-doped diamond substrates. The effects of the etching conditions and the boron concentration in diamond on the whisker morphology and overall substrate coverage were investigated. High boron-doping levels (greater than 8.4 × 10(20) cm(-3)) are crucial for the formation of the nanosized, densely packed whiskers with diameter of ca. 20 nm, length of ca. 200 nm, and density of ca. 3.8 × 10(10) cm(-2) under optimal oxygen plasma etching conditions (10 min at a chamber pressure of 20 Pa). Confocal Raman mapping and scanning electron microscopy illustrate that the boron distribution in the diamond surface region is consistent with the distribution of whisker sites. The boron dopant atoms in the diamond appear to lead to the initial fine column formation. This simple method could provide a facile, cost-effective means for the preparation of conductive nanostructured diamond materials for electrochemical applications as well as electron emission devices.

The removal and photodecomposition of n-nonylphenol using hydrophobic clay incorporated with copper-phthalocyanine in aqueous media

In order to achieve the effective removal and decomposition of n-nonylphenol (Np), an endocrine disruption chemical with poor solubility, tenuously dispersed in environmental water, the synthesis and characterization of a hydrophobic clay (HpC) with copper-phthalocyanine (CuPC) were investigated. The HpC powders were prepared by intercalating the cetyltrimethylammonium cations (CTA + ) into montmorillonite (Mont) interlayers. The HpC compound incorporated with CTA + molecules and equal to the cation-exchangeable capacity (CEC) of Mont were found to adsorb almost completely the Np molecules from the aqueous solution by the hydrophobic interaction between the alkyl chains of the CTA + and Np molecules. The CuPC molecules were incorporated with the HpC compound in order to add the photodecomposition properties of CuPC to the HpC compound. This HpC/CuPC hybrid efficiently adsorbed the Np molecules from the polluted water, too. Visible-light irradiation of the Np aqueous HpC/CuPC hybrid suspension under O2 atmosphere at 620 nm decomposed the Np molecules having been adsorbed at the hydrophobic spaces of the HpC/CuPC hybrid materials, forming quinonmethane molecules by the singlet oxygen produced by the photosensitization reaction of the cointercalated CuPC molecules.

The intercalation of metalloporphyrin complex anions into layered double hydroxides

Investigations to elucidate the structures of the cobalt(III) and manganese(III) complexes of tetra(p-sulfonatophenyl)porphinate anions (M(III)TSPP; M = Co and Mn), intercalated in Mg-Fe/Cl and Mg-Al/Cl layered double hydroxides (LDHs) have been carried out. Powder X-ray diffraction analysis, IR and UV-vis diffuse reflectance spectroscopy of Co(III)TSPP and Mn(III)TSPP intercalated into the interlayer spaces of LDH resulted in their perpendicular alignment against the host layers in the plane of the hybrid.

Photopolymerization of 4-vinylbenzoate and m- and p-phenylenediacrylates in hydrotalcite interlayers

Abstract Photopolymerizations of intercalated 4-vinylbenzoate (VBA) and p-(or m-) phenylenediacrylates (PDA) were investigated in the presence of an anion exchange clay, hydrotalcite. UV irradiation of clay powder adsorbing VBA and 4-benzoylbenzoate (BBA) ions gave rise to the cyclodimerization of the olefin and a radical polymerization to form polyvinylbenzoate. The degree of the polymerization was 10–103. The stereoregularity was investigated by NMR analysis and is discussed in relation to the state of molecular aggregation in the clay interlayers. In contrast to VBA, photoreaction of the intercalated PDAs resulted in the formation of oligomers in [2+2] cycloaddition manner, of which the polymerization degrees were rather low (up to ten at most). The stereochemistry of the oligomer was revealed to be of a syn-head-to-head structure by NMR analysis. Dianionic molecules such as PDAs showed an interesting intercalation behavior in contrast to monoanions, i.e. just one double-negatively charged molecule was estimated to occupy three anion exchange sites of the hydrotalcite layer. Also, the relatively low polymerization degrees of the PDAs were found to be due to the above intercalation characteristics. Powder X-ray diffraction analysis showed that the molecular aggregation state was remarkably changed by desiccating the clay composite in vacuum, thus suppressing the efficiency of the photoreaction.