Yusuke Ide

Efficient visible-light-induced photocatalytic activity on gold-nanoparticle-supported layered titanate.

The visible-light-induced photocatalytic conversion of aqueous benzene to phenol on Au-nanoparticle-supported layered titanate was accelerated when the reaction was conducted in the presence of aqueous phenol.

Molecular recognitive photocatalysis driven by the selective adsorption on layered titanates

The composition of layered alkali titanates (M(x)Ti(2-x/3)Li(x/3)O(4); M = K(+), Li(+), Na(+)) was tuned to control the swelling of the titanates in water and subsequently achieve molecular-sieve-like molecular recognitive photocatalytic decomposition of aqueous organic compounds on the titanates. Layered potassium lithium titanates with different layer charge density, K(x)Ti(2-x/3)Li(x/3)O(4) (x = 0.61, 0.67, and 0.74), was first synthesized and then the interlayer K(+) was quantitatively exchanged with Li(+) and Na(+) to form Li(x)Ti(2-x/3)Li(x/3)O(4) (x = 0.61, 0.67, and 0.76) and Na(x)Ti(2-x/3)Li(x/3)O(4) (x = 0.61, 0.67, and 0.76). The water adsorption/desorption isotherms and X-ray diffraction patterns of the titanates revealed that the pristine K(+)-type titanates hardly hydrated, while the Li(+)- and Na(+)-exchanged titanates expanded the interlayer space upon the hydration and the degree in the hydration was larger for the Na forms than for the Li ones and depended on the layer charge density. The present titanates were found to selectively adsorb benzene from an aqueous mixture of benzene, phenol, and 4-butylphenol and subsequently decompose benzene upon UV irradiation. The efficiency of the molecular recognitive photocatalytic benzene decomposition was related to the degree in the swelling of the titanates in water.

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

Molecular recognition of 4-nonylphenol on a layered silicate modified with organic functionalities.

A layered alkali silicate, octosilicate (Na2Si8O17), modified with the controlled amount and ratio of octadecyl and phenyl groups was synthesized to control the spatial distribution of the two functional groups and then achieve the effective and selective adsorption of 4-nonylphenol from aqueous solution. Octosilicates modified with the varied amount and ratio of the attached octadecyl/phenyl groups (0.7/0.7, 0.4/0.4, 0.3/0.3, and 0.4/1.0 groups per Si8O17 unit, respectively) were prepared by the reaction of the dodecylammonium-exchanged octosilicate with a controlled amount of octadecyltrichlorosilane and phenyltrichlorosilane sequentially. The adsorption of 4-nonylphenol from water on the four silylated octosilicates was investigated to find that the adsorption isotherm for the silylated octosilicate bearing the surface coverage with octadecyl/phenyl groups of 0.7/0.7 groups per Si8O17 unit was H-type, while the other silylated octosilicates gave S-type adsorption isotherms. The silylated octosilicate having surface coverage with octadecyl/phenyl groups of 0.7/0.7 groups per Si8O17 unit selectively adsorbed 4-nonylphenol from aqueous mixture of 4-butylphenol, 4-hexylphenol, and 4-nonylphenol.

Controlled spatial separation of Eu ions in layered silicates with different layer thickness

The photoluminescence of a series of Eu(3+) doped layered silicates (kanemite, octosilicate, magadiite and kenyaite) was examined; it was found that layer thickness affected the luminescence intensity, suggesting the possible effects of the spatial separation of Eu(3+) in the direction perpendicular to silicate sheets on the luminescence self-quenching.

Molecular selective photocatalysis by TiO2/nanoporous silica core/shell particulates

The coating of TiO(2) particles (P25) by a nanoporous silica layer was conducted to impart molecular recognitive photocatalytic ability. TiO(2)/nanoporous silica core/shell particles with varied pore diameters of the shell were synthesized by the reaction of P25 with an aqueous mixture of tetraethoxysilane and alkyltrimethylammonium chloride with varied alkyl chain lengths, followed by calcination. The TEM and nitrogen adsorption/desorption isotherms of the products showed that a nanoporous silica shell with a thickness of ca. 2nm and controlled pore diameter (1.2, 1.6, and 2.7 nm) was deposited on the titania particle when surfactants with different alkyl chain lengths (C12, C16 and C22) were used. The water vapor adsorption/desorption isotherms of the core/shell particles revealed that a larger amount of water adsorbed on the core/shell particles when the pore diameter is larger. The (29)Si MAS NMR spectra of the core/shell particles showed that the amount of surface silanol groups was independent of the water vapor adsorption capacity of the products. The possible molecular recognitive photocatalysis on the products was investigated under UV irradiation using two kinds of aqueous mixtures containing different organic compounds with varied sizes and functional groups: a 4-butylphenol, 4-hexylphenol, and 4-nonylphenol mixture and a 2-nitrophenol, 2-nitro-4-phenylphenol, and 4-nitro-2,6-diphenylphenol mixture. It was found that the core/shell particles exhibited selective adsorption-driven molecular recognitive photocatalytic decomposition of 4-nonylphenol and 2-nitrophenol in the two mixtures.

Swelling in Water of a Layered Alkali Silicate, Octosilicate, Modified with a Sulfonic Acid Group

A layered alkali silicate, octosilicate (Na(2)Si(8)O(17) x nH(2)O), was functionalized with sulfonic acid to impart swelling ability in water. To immobilize the sulfonic acid group on octosilicate, (3-mercaptopropyl)trimethoxysilane was attached in the interlayer space and subsequently oxidized. Surface coverage with the sulfonic acid group (0.7, 1.3, and 1.7 groups per Si(8)O(17)) was controlled by changing the added amount of the silane coupling reagent (0.7, 1.3, and 2.0 groups per Si(8)O(17)). The sulfonated octosilicates hydrated to expand the interlayer space, where the degree of expansion varied with the surface coverage of sulfonic acid. For the sulfonated octosilicate with the lowest surface coverage (0.7 group per Si(8)O(17)), the remaining interlayer silanol group was efficiently grafted with the trimethylsilyl group to expand the interlayer space further upon hydration. The effect of the electrolyte concentration on the hydration of the sulfonated octosilicates was investigated to find that with the increase in NaCl concentration the basal spacing decreased. The sulfonated and trimethylsilylated octosilicates were dispersed in water to form colloidal suspensions with varied transparency.

Controlled Photocatalytic Oxidation of Benzene in Aqueous Clay Suspension

Heterogeneous photocatalysis has attracted increased attention as an environmentally and economically favorable way for the removal of organic pollutants, and the production of chemical commodities and fuels. Structural, compositional, and morphological design of photocatalysts has actively been conducted to achieve efficient reactions. 2] In addition, reaction environments such as magnetic field, ultrasonic wave, and microwave have been shown to promote photocatalytic activity. Herein, we report an improved efficiency of photocatalytic benzene oxidation on TiO2 achieved by conducting the reaction in aqueous suspension of TiO2 and clay minerals. It is well-known that the aqueous suspensions and dispersions of clays exhibit useful physicochemical properties, such as thixotoropy and viscosity, and that the properties depend on the amounts and kinds of clay minerals. As a new application of clay suspensions, stable photo-induced charge separation between K4Nb6O17 nanosheets donor and an acceptor methylviologen was achieved when aqueous K4Nb6O17 and hectorite clay suspensions were mixed. In this study, aqueous clay suspensions were employed as the reaction media of photocatalytic benzene oxidation with TiO2. Two swelling clay minerals, a naturally-occurring Na-montmorillonite (Kunipia F, Kunimine Ind. Co., (Na0.53Ca0.09) [(Al3.28Fe0.31Mg0.43)oct(Si7.65Al0.35)tetO20(OH)4] 0.71 ) and a synthetic Na-saponite (Sumecton SA, Kunimine Ind. Co. , (Na0.49Mg0.14) 0.77 [(Mg5.97Al0.03)oct(Si7.20Al0.80)tetO20(OH)4] 0.77 ), and a non-swelling clay, talc (Kanto Chem. Co., Inc. , 3 MgO·4 SiO2·H2O) were used. The photo-oxidation of benzene was chosen as a reaction to be modified in this study, because the mineralization and partial oxidation of benzene have widely been investigated using various catalysts 9] and extra-stimuli. 10] Shown in Figure 1 is the time course of benzene consumption as a result of photocatalytic oxidation by irradiation of TiO2 (P25, Nippon aerosil) in the absence and the presence of the aqueous suspension of saponite. The bare TiO2 oxidized aqueous benzene to some extent (Figure 1 a). On the other hand, when the reaction was conducted in a saponite suspension, the benzene oxidation efficiency was largely enhanced depending on the added amount of saponite (Figure 1 b and c). The partially oxidized products, phenol, catechol, and 1,2,4trihydroxybenzene were detected by using high performance liquid chromatography and the smaller amount of phenol and catechol, and larger amount of 1,2,4-trihydroxybenzene formed when a larger amount of saponite was used. Taking the fact that benzene is oxidized to phenol, catechol, and 1,2,4-trihydroxybenzene sequentially and finally mineralized to CO2 into consideration, the above results indicate that a saponite suspension accelerates the oxidation of benzene on TiO2. When using 1 mass % of saponite suspension, almost all the added benzene was oxidized and 1,2,4-trihydroxybenzene remained as a main organic compound in the aqueous phase (selectivity of 80 %, Table 1). This result is worth mentioning as a merit of the present strategy for the potential application of water purification, as phenol is a known water contaminant of industry waste water, whereas 1,2,4-trihydroxybenzene is harmless to humans.

Fe oxide nanoparticles/Ti-modified mesoporous silica as a photo-catalyst for efficient and selective cyclohexane conversion with O2 and solar light

We report a new, environmentally and economically friendly photocatalytic process with unprecedentedly high activity for partial cyclohexane oxidation. Mesoporous silicas containing isolated tetrahedrally coordinated Ti and Fe oxide nanoparticles immobilized on the pore surface were synthesized by reacting SBA-15 with Ti(IV) acetylacetonate and Fe(III) acetylacetonate successively. A variety of characterizations suggested that the grafted tetrahedrally coordinated Ti species were coupled with Fe oxide nanoparticles via Ti–O–Fe bonds. The SBA-15 photocatalysts showed a high yield (up to sub-mmol) and nearly 100% selectivity for the production of cyclohexanol and cyclohexanone with molecular O2 under solar light. The unprecedentedly high activity could be explained by the lengthened lifetime of the active Ti species by electron delocalization over Ti–O–Fe bonds and the visible light (λ > 420 nm)-induced activity endowed by Fe oxide nanoparticles coupled to the Ti species.

h-BN nanosheets as simple and effective additives to largely enhance the activity of Au/TiO2 plasmonic photocatalysts

The activity of Au nanoparticle-loaded P25 TiO2 (Au/P25) plasmonic photocatalysts, evaluated by the oxidative decomposition of formic acid in water under visible light irradiation, was enhanced up to 3 times by simply mixing Au/P25 with photocatalytically inactive h-BN nanosheets as a result of electron transfer from photoexcited Au/TiO2 to the h-BN nanosheets and retardation of the charge recombination.