Sho Kataoka

Microreactor with mesoporous silica support layer for lipase catalyzed enantioselective transesterification

Lipase PS was immobilized in mesoporous silica (MPS) thin films inside a borosilicate tube microreactor for use in the enantioselective transesterification of vinyl acetate with (±)-1-phenylethanol. The immobilization was tested for 3D cubic and 2D hexagonal MPS thin films inside microreactors with and without hydrophobic treatment. The hydrophobic treatment enhanced the adsorption amount and the lipase activity for both 3D cubic and 2D hexagonal films. Of these treated films, the 3D cubic structure film exhibited the highest yield (64%) with an enantioselectivity higher than 99% in a continuous flow experiment. The activity of the immobilized lipase PS was well maintained for 36-hour continuous operation. A Ping-Pong Bi Bi kinetic model was employed to interpret the activity of the immobilized lipase PS. The ratios of the maximum velocity to the Ping-Pong constant (i.e., specificity constants) were measured for lipase PS immobilized inside the microreactor and for native lipase PS. The value inside the microreactor was 800 times greater than that of the native lipase PS.

Characterization of carbon cryogel microspheres as adsorbents for VOC.

Adsorption characteristics of carbon cryogel microspheres (CC microspheres) with controlled porous structure composed of mesopores (2 nm<d(p)<50 nm; d(p) is pore diameter) and micropores (d(p)<2 nm) were studied to examine their suitability as adsorbents for a volatile organic compound (VOC). The amount of toluene, as a model VOC, adsorbed on the CC microspheres could be changed by varying either the size of the mesopores or the volume of the micropores. The peak temperature of the temperature-programmed desorption profiles of toluene from the CC microspheres was higher than that from granular activated carbon (GAC) with numerous micropores, indicating that toluene is adsorbed more strongly on CC microspheres than on GAC. To permit the practical use of CC microspheres, the adsorption characteristic of moisture on CC microspheres and GAC were evaluated. The effect of adsorption of moisture on the gas permeation property of an adsorption module prepared from the CC microspheres was also examined.

Enhanced energy harvesting by concentration gradient-driven ion transport in SBA-15 mesoporous silica thin films

Nanofluidic energy harvesting systems have attracted interest in the field of battery application, particularly for miniaturized electrical devices, because they possess excellent energy conversion capability for their size. In this study, a mesoporous silica (MPS)-based nanofluidic energy harvesting system was fabricated and selective ion transport in mesopores as a function of the salt gradient was investigated. Aqueous solutions with three different kinds of monovalent electrolytes-KCl, NaCl, and LiCl-with different diffusion coefficients (D+) were considered. The highest power density was 3.90 W m-2 for KCl, followed by 2.39 W m-2 for NaCl and 1.29 W m-2 for LiCl. Furthermore, the dependency of power density on the type of cation employed indicates that the harvested energy increases as the cation mobility increases, particularly at high concentrations. This cation-specific dependency suggests that the maximum power density increases by increasing the diffusion coefficient ratio of cations to anions, making this ratio a critical parameter in enhancing the performance of nanofluidic energy harvesting systems with extremely small pores ranging from 2 to 3 nm.

Ion Transport in Mesoporous Silica SBA-16 Thin Films with 3D Cubic Structures

Mesoporous silica SBA-16 thin films with highly ordered 3D cubic structures were synthesized on a Si substrate via the dip-coating method. After these films were filled with KCl aqueous solutions, the ionic current passing through the mesopores was measured by applying dc electric fields. At low ion concentrations, the measured I-V curves were nonlinear and the current increased exponentially with respect to voltage. As the ion concentration increased, the I-V curve approached linear behavior. The nonlinear behavior of I-V curves can be reasonably attributed to the electric potential barrier created in nanopores.

Layered Hybrid Perovskites with Micropores Created by Alkylammonium Functional Silsesquioxane Interlayers

Layered organic-inorganic hybrid perovskites that consist of metal halides and organic interlayers are a class of low-dimensional materials. Here, we report the fabrication of layered hybrid perovskites using metal halides and silsesquioxane with a cage-like structure. We used a silsesquioxane as an interlayer to produce a rigid structure and improve the functionality of perovskite layers. Propylammonium-functionalized silsesquioxane and metal halide salts (CuCl2, PdCl2, PbCl2, and MnCl2) were self-assembled to form rigid layered perovskite structures with high crystallinity. The rigid silsesquioxane structure produces micropores between the perovskite layers that can potentially be filled with different molecules to tune the dielectric constants of the interlayers. The obtained silsesquioxane-metal halide hybrid perovskites exhibit some characteristic properties of layered perovskites including magnetic ordering (CuCl4(2-) and MnCl4(2-)) and excitonic absorption/emission (PbCl4(2-)). Our results indicate that inserting silsesquioxane interlayers into hybrid perovskites retains and enhances the low-dimensional properties of the materials.

One-dimensional alignment of SBA-15 films in microtrenches.

SBA-15 thin films were synthesized by dip-coating in two different types of microtrenches: (a) silicon microtrenches and (b) silicon microtrenches with a deposited low-temperature oxide (LTO) layer. In the upper part of the synthesized films, the pores were aligned along the concave surface in both microtrenches. This alignment was attributed to the capillary force acting during solvent evaporation. In the lower part of the films, the pores were aligned tangentially with the wall in a silicon microtrench whereas they were aligned normal to the wall in a silicon microtrench with a deposited LTO layer. The LTO layer could suppress the growth of mesostructures from the substrate and promote growth from the vapor-liquid interface. The effects of the composition of the precursor solution and relative humidity on pore alignment were also clarified.

Nanometer-Sized Domains in Langmuir−Blodgett Films for Patterning SiO2

In this study, we prepared Langmuir-Blodgett films with domains ranging from 20 to 100 nm in size by using perfluorinated fatty acids. The domain size of the obtained LB films is markedly smaller than the ordinary domain size of hydrocarbons and fluorocarbons on the micrometer scale. The domains were prepared by controlling their growth through the addition of 2-propanol to the subphase of Langmuir monolayers. Furthermore, the prepared domains in the LB films were used as templates for patterning SiO(2) films. The obtained SiO(2) films have completely negative structures compared with those of the domains in the LB films.

Controlled Formation of Silica Structures Using Siloxane/Block Copolymer Complexes Prepared in Various Solvent Mixtures

Block copolymers exhibit regularly patterned structures induced by microphase separation. Here we present a method for preparing various particulate silica (SiO2) nanostructures by controlling the microphase separation of block copolymers. In this method, siloxane, a SiO2 precursor, is adsorbed onto poly(4-vinylpyridine) blocks of polystyrene-block-poly(4-vinylpyridine) in solvent mixtures. After siloxane/polymer complexes are coprecipitated via further siloxane polycondensation, the resulting precipitates are heated to remove the polymer. The results of scanning electron microscopy revealed that SiO2 formed various structures including cylindrical, spherical, and lamellar. Different SiO2 nanostructures formed via the microphase separation of siloxane/polymer complexes are prepared simply by varying solvent mixtures without changing the polymer chain. The structural change is interpreted in terms of polymer-solvent interactions and volume fractions in siloxane/polymer complexes.

Controlled formation of ordered coordination polymeric networks using silsesquioxane building blocks

In this report, we synthesized ordered coordination polymers using polyhedral oligomeric silsesquioxanes (POSS) as a building block. A POSS with eight carboxylic terminals was coordinated with copper ions at various temperatures, forming polymeric networks. This novel coordination polymer has a long-range ordered structure.

Direct synthesis of tetraalkoxysilanes from silica and alcohols

A new simple and efficient process for synthesizing tetraalkoxysilanes (TROS) directly from silica and alcohols was developed using molecular sieves as dehydrating agents. Using this method, a variety of TROS (R = ethoxy, n-propoxy, or n-butoxy) were obtained over 70% yields within 6 h. We also employed various natural silica sources in this process for practical applications.