Metamagnetic Behavior in a Quadruple Perovskite Oxide.

A cubic quadruple perovskite oxide CeMn3Cr4O12 has been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1273 K. The X-ray absorption spectroscopy reveals that the Ce ions are in a trivalent state, as represented by the ionic model of Ce3+Mn3+3Cr3+4O12. The magnetic study demonstrates three independent antiferromagnetic transitions attributed to Ce (∼10 K), Mn (46 K), and Cr (133 K) ions. Furthermore, a magnetic field-induced antiferromagnetic-to-ferromagnetic (metamagnetic) transition of Ce3+ 4f moments is observed at low temperatures below 20 K, exhibiting a rare example of metamagnetism in the Ce3+-oxides. This finding represents that the 3d-electron magnetic sublattices play a role in the metamagnetism of 4f-electron magnetic moments, demonstrating a new aspect of the 3d-4f complex electron systems.

Design of Advanced Functional Materials Using Nanoporous Single-Site Photocatalysts.

Nanoporous silica solids can offer opportunities for hosting photocatalytic components such as various tetra-coordinated transition metal ions to form systems referred to as "single-site photocatalysts". Under UV/visible-light irradiation, they form charge transfer excited states, which exhibit a localized charge separation and thus behave differently from those of bulk semiconductor photocatalysts exemplified by TiO2 . This account presents an overview of the design of advanced functional materials based on the unique photo-excited mechanisms of single-site photocatalysts. Firstly, the incorporation of single-site photocatalysts within transparent porous silica films will be introduced, which exhibit not only unique photocatalytic properties, but also high surface hydrophilicity with self-cleaning and antifogging applications. Secondary, photo-assisted deposition (PAD) of metal precursors on single-site photocatalysts opens up a new route to prepare nanoparticles. Thirdly, visible light sensitive photocatalysts with single and/or binary oxides moieties can be prepared so as to use solar light, the ideal energy source.

Single-site and nano-confined photocatalysts designed in porous materials for environmental uses and solar fuels.

Silica-based micro-, meso-, macro-porous materials offer attractive routes for designing single-site photocatalysts, supporting semiconducting nanoparticles, anchoring light-responsive metal complexes, and encapsulating metal nanoparticles to drive photochemical reactions by taking advantage of their large surface area, controllable pore channels, remarkable transparency to UV/vis and tailorable physicochemical surface characteristics. This review mainly focuses on the fascinating photocatalytic properties of silica-supported Ti catalysts from single-site catalysts to nanoparticles, their surface-chemistry engineering, such as the hydrophobic modification and synthesis of thin films, and the fabrication of nanocatalysts including morphology controlled plasmonic nanostructures with localized surface plasmon resonance. The hybridization of visible-light responsive metal complexes with porous materials for the construction of functional inorganic-organic supramolecular photocatalysts is also included. In addition, the latest progress in the application of MOFs as excellent hosts for designing photocatalytic systems is described.

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 performance of TiO2-zeolite templated carbon composites in organic contaminant degradation.

TiO2 composites with zeolite templated carbon (TiO2-ZTC) and activated carbon (TiO2-AC) were prepared and used as the photocatalysts for comparative studies with pure TiO2. TiO2-ZTC exhibited the highest rate of methylene blue degradation with a rate approximately 4 and 400 times higher than those of TiO2-AC and pure TiO2, respectively. Moreover, the highest catalytic performance of TiO2-ZTC in gas-phase degradation of acetone was approximately 1.1 and 12.9 times higher than TiO2-AC and pure TiO2, respectively. These outstanding performances could be attributed to high surface area, pore volume, and hydrophobic surface properties, leading to improvement in the adsorption properties of organic molecules.

Design of composite photocatalyst of TiO2 and Y-zeolite for degradation of 2-propanol in the gas phase under UV and visible light irradiation.

Hydrophobic Y-zeolite (SiO2/Al2O3 = 810) and TiO2 composite photocatalysts were designed by using two different types of TiO2 precursors, i.e., titanium ammonium oxalate and ammonium hexafluorotitanate. The porous structure, surface property and state of TiO2 were investigated by various characterization techniques. By using an ammonium hexafluorotitanate as a precursor, hydrophobic modification of the Y-zeolite surface and realizing visible light sensitivity was successfully achieved at the same time after calcination at 773 K in the air. The prepared sample still maintained the porous structure of Y-zeolite and a large surface area. Highly crystalline anatase TiO2 was also formed on the Y-zeolite surface by the role of fluorine in the precursor. The usages of ammonium hexafluorotitanate were effective for the improvement of the photocatalytic performance of the composite in the degradation of 2-propanol in the gas phase under UV and visible light (λ > 420 nm) irradiation.

Surfactant-free nonaqueous synthesis of plasmonic molybdenum oxide nanosheets with enhanced catalytic activity for hydrogen generation from ammonia borane under visible light.

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth-abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface-capping agents in their synthetic procedures. To fulfill this, a facile non-aqueous procedure was employed to prepare well-defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO(3-x) nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near-infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen-generation activity of ammonia borane under visible light irradiation.

Active skeletal Ni catalysts prepared from an amorphous Ni-Zr alloy in the pre-crystallization state.

Skeletal Ni catalysts were prepared from an amorphous Ni40Zr60 alloy (a-NiZr) by heating at various temperatures under vacuum, followed by the selective extraction of Zr moieties by an HF treatment. Each sample was characterized by various spectroscopic methods, and the catalytic performance was tested in the hydrogenation of 1-octene. The differences in preparation temperatures of a-NiZr strongly affected the catalytic performance of the obtained catalysts, whereby those prepared from heated a-NiZr in the pre-crystallization state exhibited higher catalytic activity. Especially, moderate thermal treatment of a-NiZr at a temperature slightly lower than that for its crystallization, that is, ~573 K, resulted in a significant enhancement of the catalytic activity. Such prepared skeletal Ni catalyst can also be used efficiently for hydrogen generation from aqueous hydrazine.

Preparation of aluminum-containing mesoporous silica with hierarchical macroporous architecture and its enhanced catalytic activities.

Aluminum-containing mesoporous silica with hierarchical macroporous architecture (Al-MMS) was successfully prepared using a solvent evaporation method through the combination of precursor solution for synthesis of Al-containing mesoporous silica (Al-MS) and poly(methyl methacrylate) (PMMA) colloidal crystals as a hard template. The porous structure and the state of aluminum were investigated using various characterization techniques. The construction of combined structure of Al-MMS, i.e., hierarchical macroporous architecture consisting of thin mesoporous silica frameworks, led to the formation of many mesopore entrances and the shortening of the mesoporous channels. In the tetrahydropyranylation of linear alcohols with dihydropyran (DHP), Al-MMS exhibited higher catalytic activities for the formation of corresponding tetrahydropyranyl ethers as compared to Al-MS. The advantageous structure of Al-MMS enables the efficient transport of reactants to the catalytically active sites, which realizes the significant enhancement of catalytic performances in the reaction of DHP with alcohols having longer alkyl chains.

The synthesis of size- and color-controlled silver nanoparticles by using microwave heating and their enhanced catalytic activity by localized surface plasmon resonance.

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.

Dramatic enhancement of CO2 uptake by poly(ethyleneimine) using zirconosilicate supports.

The CO(2) adsorption characteristics of prototypical poly(ethyleneimine)/silica composite adsorbents can be drastically enhanced by altering the acid/base properties of the oxide support via incorporation of Zr into the silica support. Introduction of an optimal amount of Zr resulted in a significant improvement in the CO(2) capacity and amine efficiency under dilute (simulated flue gas) and ultradilute (simulated ambient air) conditions. Adsorption experiments combined with detailed characterization by thermogravimetric analysis, temperature-programmed desorption, and in situ FT-IR spectroscopy clearly demonstrate a stabilizing effect of amphoteric Zr sites that enhances the adsorbent capacity, regenerability, and stability over continued recycling. It is suggested that the important role of the surface properties of the oxide support in these polymer/oxide composite adsorbents has been largely overlooked and that the properties may be even further enhanced in the future by tuning the acid/base properties of the support.

Enhanced CO2 adsorption over polymeric amines supported on heteroatom-incorporated SBA-15 silica: impact of heteroatom type and loading on sorbent structure and adsorption performance.

Silica supported amine materials are promising compositions that can be used to effectively remove CO(2) from large stationary sources, such as flue gas generated from coal-fired power plants (ca. 10 % CO(2)) and potentially from ambient air (ca. 400 ppm CO(2)). The CO(2) adsorption characteristics of prototypical poly(ethyleneimine)-silica composite adsorbents can be significantly enhanced by altering the acid/base properties of the silica support by heteroatom incorporation into the silica matrix. In this study, an array of poly(ethyleneimine)-impregnated mesoporous silica SBA-15 materials containing heteroatoms (Al, Ti, Zr, and Ce) in their silica matrices are prepared and examined in adsorption experiments under conditions simulating flue gas (10 % CO(2) in Ar) and ambient air (400 ppm CO(2) in Ar) to assess the effects of heteroatom incorporation on the CO(2) adsorption properties. The structure of the composite adsorbents, including local information concerning the state of the incorporated heteroatoms and the overall surface properties of the silicate supports, are investigated in detail to draw a relationship between the adsorbent structure and CO(2) adsorption/desorption performance. The CO(2) adsorption/desorption kinetics are assessed by thermogravimetric analysis and in situ FT-IR measurements. These combined results, coupled with data on adsorbent regenerability, demonstrate a stabilizing effect of the heteroatoms on the poly(ethyleneimine), enhancing adsorbent capacity, adsorption kinetics, regenerability, and stability of the supported aminopolymers over continued cycling. It is suggested that the CO(2) adsorption performance of silica-aminopolymer composites may be further enhanced in the future by more precisely tuning the acid/base properties of the support.

Enhanced catalytic activity on titanosilicate molecular sieves controlled by cation-π interactions.

A new class of heterogeneous catalytic systems utilizing cation-guest interactions was designed based on microporous titanosilicate molecular sieves. Introducing heavier alkali metal cations on ion-exchange sites of the framework resulted in a significant enhancement of the catalytic activity for oxidation of cyclohexene and styrene, whereas such an enhancement was not observed in oxidation of cyclohexane without π systems. Distinct relationships between the catalytic activities and intermolecular interaction energies which were determined by IR spectroscopic and computational approaches clearly evidenced the predominance of the cation-π interaction in this catalytic system.

Synthesis and unique catalytic performance of single-site Ti-containing hierarchical macroporous silica with mesoporous frameworks.

Single-site Ti-containing hierarchical macroporous silica with mesoporous frameworks (Ti-MMS) was successfully prepared by a solvent evaporation method using organic surfactant and poly(methyl methacrylate) (PMMA) colloidal crystals as the template. The formation of a well-defined macroporous structure composed of mesoporous silica walls was characterized by SEM and TEM observations. The successful incorporation of tetrahedrally coordinated Ti oxide moieties within their frameworks was also confirmed by spectroscopic techniques such as UV-vis and XAFS measurements. Comparative studies revealed that Ti-MMS exhibited higher catalytic activities for the epoxidation of linear α-olefin compared to Ti-containing mesoporous silica without macropores (Ti-MS). The reaction rate was significantly enhanced on Ti-MMS depending on increases in the alkyl chain length of linear α-olefins. It was also found that Ti-MMS showed good catalytic performance in the selective epoxidation of methyl oleate, which is a kind of unsaturated fatty acid methyl ester (FAME), under acid-free reaction conditions with tert-butylhydroperoxide (TBHP) because of the advantages of the combination of hierarchical macroporous and mesoporous structures.

Design of superhydrophobic surfaces by synthesis of carbon nanotubes over Co-Mo nanocatalysts deposited under microwave irradiation on Ti-containing mesoporous silica thin films.

The superhydrophobic surface has been designed by the synthesis of carbon nanotubes (CNTs) on Ti-containing mesoporous silica thin films (Ti-MSTFs) with Co-Mo binary nanocatalysts. The active Co-Mo catalysts have been successfully deposited on Ti-MSTFs under microwave irradiation. SEM and TEM observations after CNT synthesis revealed that surfaces of Ti-MSTFs were densely covered with CNTs having a diameter of 15 nm. Raman spectra indicated that the undesired structural defects in the carbon network of the synthesized CNTs, which would lead to the formation of hydroxyl groups, were scarce. Interestingly, hydrophobic properties of samples after CNT synthesis were enhanced with increasing titanium concentration of Ti-MSTF, and the water contact angle reached up to 165° on Ti-MSTF with a titanium concentration of 10 at%. The combination of dispersed titanium oxide moieties within the silica frameworks and the microwave irradiation made a great contribution to deposit active Co-Mo catalysts responsible for the formation of well-dense CNTs.

Heterogeneous Fenton Degradation of Organic Pollutants in Water Enhanced by Combining Iron-type Layered Double Hydroxide and Sulfate.

Water pollution derived from organic pollutants is one of the global environmental problems. The Fenton reaction using Fe2+ as a homogeneous catalyst has been known as one of clean methods for oxidative degradation of organic pollutants. Here, a layered double hydroxide (Fe2+ Al3+ -LDH) containing Fe2+ and Al3+ in the structure was used to develop a "heterogeneous" Fenton catalyst capable of mineralizing organic pollutants. We found that sulfate ion (SO4 2- ) immobilized on the Fe2+ Al3+ -LDH significantly facilitated oxidative degradation (mineralization) of phenol as a model compound of water pollutants to carbon dioxide (CO2 ) in a heterogeneous Fenton process. The phenol conversion and mineralization efficiency to CO2 reached >99% and ca. 50%, respectively, even with a reaction time of only 60 min.

Incorporation of arene metal carbonyl complexes within inorganic-organic hybrid mesoporous materials by CVD method.

Simple chemical vapor deposition (CVD) of M(CO), (M = Cr, Mo, W) onto phenylene- and biphenylene-bridged organosilica mesoporous materials (HMM-ph, HMM-biph) led to the efficient formation of C6H4M(CO)3 and (C6H4)2M(CO)3 complexes, respectively, which are directly fixed and incorporated within the framework structure of HMM-ph and HMM-biph having molecular-scale periodicity in the pore walls. FT-IR investigations revealed that thus formed C6H4M(CO), or (C6H4)2M(CO)3 complexes are thermally stable even under thermovacuum treatment at 473 K.

TiO2 superstructures with oriented nanospaces: a strategy for efficient and selective photocatalysis.

Highly ordered superstructures of semiconductor nanocrystals contain abundant nanometer-scale pores between the crystals; however, there have been difficulties in controlling the size and orientation of these nanospaces without the use of a template or a capping reagent. This constraint has affected their development and applications in potential fields including catalysis and optoelectronics adversely. In this study, we synthesized a rod-shaped TiO2 mesocrystal (TMC) having a length of a few hundreds of micrometers and comprising regularly ordered anatase TiO2 nanocrystals that form oriented nanospaces by exposed {001} facets. Finite-difference time-domain (FDTD) calculations of electric fields and in situ fluorescence imaging with a polarization sensitive dye on a single mesocrystal were performed to reveal anisotropic adsorption and excitation of the dyes. Furthermore, the photodegradation of the dyes was found to be more facilitated in nanospaces formed by the specific facets, as compared with the dyes randomly adsorbed on the outer surfaces. Consequently, the selectivity of photocatalytic reactions based on the molecular size and redox was enhanced by introducing the concept of oriented nanospace.

Fabrication of hydrophobic zeolites using triethoxyfluorosilane and their application as supports for TiO(2) photocatalysts.

Hydrophobically modified Y-zeolites were prepared by simple modification with triethoxyfluorosilane (TEFS). These zeolites, used as supports, enhanced the efficiency of deposited TiO(2) for the photocatalytic degradation of organics diluted in water.