Masahide Takahashi

Applications of magnetic metal–organic framework composites

The high and regular porosity of metal–organic frameworks (MOFs) provides exceptional properties suitable for technological applications. The increasing interest of the scientific community is based on the exploration of these advantageous properties for industrial applications. Pure MOFs are specifically designed to offer a huge surface area; such a high specific surface area has been explored and exploited for gas storage, separation, or catalysis in a variety of chemical processes. A different and promising scientific trend aims to combine MOFs with extrinsic functionalities such as functional nanoparticles; this strategy enables the preparation of new nanocomposite materials with unprecedented properties. An interesting case is offered by the synergic combination of magnetic particles with MOF crystals. In the resulting nanocomposite material, the adaptive functional responses can be triggered by an external magnetic field. In this context, different protocols have been developed for the efficient preparation of magnetic framework composites (MFCs), a class of materials that combines magnetic nano- or micro-particles with MOFs crystals. This application paper highlights the progress on MFCs for drug delivery, environmental control, catalysis, sensing and miniaturized device fabrication.

Enhanced photocurrent in thin film TiO2 electrodes prepared by sol–gel method

Abstract Thin film n-type TiO 2 electrodes of different thickness from 10 to 540 nm were prepared by the sol–gel method so as to investigate the effects of the film thickness on the photocurrent. Since a steep band gradient is expected to form in the thin film TiO 2 electrode with thickness less than the space charge layer, such steep band bending would effectively separate the photo-generated electrons and holes, leading to an increase in the photocurrent of the thin TiO 2 film electrodes. It was found that in the range of 10–540 nm in thickness, the TiO 2 film electrode of 70 nm thick showed a maximum photocurrent, which was approximately six times as large as that of the electrodes of 180–540-nm thickness. This result clearly indicates that the reduction of film thickness is effective for obtaining of the efficient n-type TiO 2 film electrode.

Application of femtosecond laser pulses for microfabrication of transparent media

Femtosecond laser microfabrication of 3D optical memories and photonic crystal (PhC) structures in solid glasses and liquid resins are demonstrated. The optical memories can be read out from both transmission and emission images. The PhC structures reveal clear signatures of photonic bandgap (PBG) and microcavity formation.

Preparation and structure of organic-inorganic hybrid precursors for new type low-melting glasses

Abstract Organic–inorganic hybrid precursors for new type low-melting glasses without pollution elements such as Pb and F have been synthesized through a non-aqueous acid–base reaction process. The hybrid compounds consist of –Si–O–P– framework, in which some of the bridging oxygens of a Si tetrahedron are substituted by organic functional groups. Terminating the oxide framework by the organic functional groups lowers the network dimension. Orthophosphoric acid (H 3 PO 4 ) and dialkyldichlorosilane (Me 2 SiCl 2 and Et 2 SiCl 2 ) were employed as starting materials. The formation of P–O–Si linkage was confirmed by IR spectra. The larger viscosity increase at higher Si concentrations is correlated to the formation of the linkage. It is proposed that an acid–base polycondensation reaction of P–OH+Si–Cl→P–O–Si+HCl↑ dominates the network formation. When dimethylsilane SiMe 2 is substituted by divalent Sn, an organic–inorganic hybrid low-melting glass in the system of SnO–Me 2 SiO–P 2 O 5 can be derived, the glass transition temperature of which is about 29 °C. So the present acid–base reactions provide a new process by which precursors for new type low-melting glass are synthesized.

Gel-melting method for preparation of organically modified siloxane low-melting glasses

Softening or melting behavior of the organically-modified siloxane hybrid gels and glasses in the system of RSiO 3/2 and R 2 SiO 2/2 (R: methyl and phenyl) has been investigated to obtain a new family of low-melting glasses. The RSiO 3/2 and RSiO 3/2 –R 2 SiO 2/2 gels showed softening temperatures around 50–100 °C. The softening temperature of RSiO 3/2 single-component glasses, which were obtained by melting the corresponding gels at a temperature above the softening temperature, increased by heat-treatment at 200 °C, and finally showed no softening behavior. On the other hand, in the PhSiO 3/2 –Ph 2 SiO 2/2 binary glasses, the softening temperatures showed a tendency to saturate after longer heat treatment over 200 h. These facts indicate that the present organically modified siloxane system will be a potential candidate for the low-melting glass.

Waveguide formation in niobium tellurite glasses by pico- and femtosecond laser pulses

Abstract We obtained a temporal and permanent refractive index change in niobium tellurite glasses by using ps- and fs-pulses, respectively. A He–Ne laser beam was guided by a line waveguide structure drawn by the fs-pulses, indicating positive refractive index change. It is suggested that the refractive index change by the ps-pulses is due to an increase in the absorption coefficient while that caused by the fs-pulses results from the rearrangement of the glass structure.

Dynamic Control of MOF‐5 Crystal Positioning Using a Magnetic Field

Paolo alcaro , * F rancois F Normandin , Masahide akahashi , T Paolo Scopece , Heinz Amenitsch , Stefano Costacurta , Cara M. Doherty , Jamie S. Laird , Matthew D. H. Layabio , F Lisi , Anita J. Hill , and Dario Buso *

Sol-gel reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution

The reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution have been studied by multinuclear magnetic resonance and light scattering techniques. The study has shown that in this peculiar chemical environment the alkoxy groups of 3-glycidoxypropyltrimethoxysilane undergo a fast hydrolysis and condensation which favor the formation of open hybrid silica cages. The silica condensation reaches 90% at a short aging time but does not go to completion even after 9 days. The highly basic conditions also slow down the opening of the epoxies which fully react only after several days of aging. The epoxy opening generates different chemical species and several reaction pathways have been observed; in particular, the formation of polyethylene oxide chains, diols, termination of the organic chain by methyl ether groups and formation of dioxane species. These reactions are slow and proceed gradually with aging; light scattering analysis has shown that clusters of dimensions lower than 20 nm are formed after two days of reactions, but their further growth is hindered by the highly basic conditions which limit full silica condensation and formation of organic chains.

Bioencapsulation of apomyoglobin in nanoporous organosilica sol–gel glasses: Influence of the siloxane network on the conformation and stability of a model protein

Nanoporous sol-gel glasses were used as host materials for the encapsulation of apomyoglobin, a model protein employed to probe in a rational manner the important factors that influence the protein conformation and stability in silica-based materials. The transparent glasses were prepared from tetramethoxysilane (TMOS) and modified with a series of mono-, di- and tri-substituted alkoxysilanes, R(n)Si(OCH(3))(4-n) (R = methyl-, n = 1; 2; 3) of different molar content (5, 10, 15%) to obtain the decrease of the siloxane linkage (-Si-O-Si-). The conformation and thermal stability of apomyoglobin characterized by circular dichroism spectroscopy (CD) was related to the structure of the silica host matrix characterized by (29)Si MAS NMR and N(2) adsorption. We observed that the protein transits from an unfolded state in unmodified glass (TMOS) to a native-like helical state in the organically modified glasses, but also that the secondary structure of the protein was enhanced by the decrease of the siloxane network with the methyl modification (n = 0 < n = 1 < n = 2 < n = 3; 0 < 5 < 10 < 15 mol %). In 15% trimethyl-modified glass, the protein even reached a maximum molar helicity (-24,000 deg. cm(2) mol(-1)) comparable to the stable folded heme-bound holoprotein in solution. The protein conformation and stability induced by the change of its microlocal environment (surface hydration, crowding effects, microstructure of the host matrix) were discussed owing to this trend dependency. These results can have an important impact for the design of new efficient biomaterials (sensors or implanted devices) in which properly folded protein is necessary.

Layered double hydroxide (LDH)-based monolith with interconnected hierarchical channels: enhanced sorption affinity for anionic species

Monolithic layered double hydroxides (LDHs) with interconnected channels have been expected to enhance sorption rate as well as increase accumulation of anions. Although powder molding can form easily-handled LDH compacts, interconnected channel formation therein has not been achieved. Herein, we demonstrate cm-scale monolithic LDH-based composites with interconnected hierarchical channels via a spontaneous sol–gel reaction. The synthesis was performed on Mg–Al hydrotalcite-type LDHs starting from metal chlorides aqueous/ethanolic solution with poly(ethylene oxide) incorporated. Addition of propylene oxide triggers a sol–gel reaction to form monolithic xerogels with a formula of [Mg0.66Al0.33(OH)2Cl0.33·2.92H2O]·3.1Al(OH)3. LDH crystals together with aluminum hydroxide crystals homogeneously build up gel skeletons with well-defined hierarchical channels. The interconnected channel in μm range (macrochannel) are formed as a phase-separated structure, whereas the channel in nm range (nanochannel) are as interstices of primary particles. The channel architectures are preserved in the course of rehydration process, affording enhanced sorption affinity for anion species in the process. Both of macro and mesochannels as well as high charge density of the obtained LDHs (Mg/Al = 2.0) contribute to enhanced anion sorption in the monolithic xerogels. The materials obtained here opens up applications of high performance adsorbents and ion-storage free from diffusion limitation.