Published papers

The optical properties of polycyclic aromatic hydrocarbon fluorophores, such as pyrene and perylene, are controlled by confined spaces of meso- and supermicropores in a silica matrix. The quantum yield of fluorescence from monodispersed pyrene and perylene increases with limitation of the excimer formation in 1 nm supermicropores. When the pore diameter is close to the molecular size, solid-state fluorescence having a high quantum yield is achieved via the fluorophores in the confined spaces by suppressing the aggregation, the interaction with charge-transfer sites and the stabilization of the excited state.

Various biological and biomimetic minerals are composed of mesocrystals, in which nanoscale crystalline units are ordered in approximately the same crystallographic direction. However, the variation of the crystallographic regularity of mesocrystals has not been clarified using experimental evidence. This work demonstrated the gradual evolution of disorder in crystalline structures between single crystal and polycrystal by monitoring the crystallographic regularity using electron diffraction patterns. Single-crystal rods of fluorapatite elongated in the c direction are switched to mesocrystals consisting of iso-oriented nanorods by adding a specific molecule having a carboxy group (chemical approach) and to roughly arranged nanograins by increasing the degree of supersaturation at the growth front (physicochemical approach). Lateral and vertical miniaturization of the growth units is achieved through stepwise nucleation and near-epitaxial growth. The crystallographic regularity gradually decreases with deviation of the c axis and rotation of the a axes through reduction of the growth unit size. Here we can tune the disorder in crystalline structures via the chemical and physicochemical approaches.

Room-temperature operations of rechargeable Mg coin-cell batteries have been achieved using a Mg alloy negative electrode and a spinel MgMn2O4(MMO)-positive electrode. The present work focuses on clarifying the effects of the physiochemical properties of the MMO powder including the specific surface area (SBET) and porosity of the positive electrode on Mg battery performances in practical applications. Finally, optimal specific surface area and porosity parameters were obtained that ensured excellent battery performances as a standard coin-cell at room temperature. A typical MMO powder synthesized using a modified sol-gel method with propylene oxide-driven complex polymerization had a largeSBET> 200 m2g−1, and more than 90% porosity with a triple-tiered 3D open-channel network. Here we evaluated the discharge capacity and the cyclability for room-temperature operation as a function ofSBETin a full cell with a Mg negative electrode as well as half cells with a carbon graphite electrode. Irrespective of whether half cells or a full cell was used, the initial discharge capacity was found to depend linearly on theSBETof the porous MMO powder in a Mg tetrakis(hexafluoroisopropyl)borate/triglyme electrolyte with a wide potential window, ΔE> 3.6 V. Eventually, the maximum discharge capacity of 220 mA h g−1was realized at 25 °C in the full cell using the 3D open-channel nanostructure withSBET= 236 m2g−1. The cyclability in the full cell with the Mg alloy negative electrode, however, degraded with the increasingSBET, while no cyclability degradation was observed in the half cell with the carbon electrode. A possible mechanism is discussed regarding passivation of the Mg alloy electrode in discharge/charge cycles.

Band engineering with a quantum size effect is proposed to be utilized to design photocatalytic activity for the conversion of organic compounds. Subnanometer WO3 quantum dots (QDs) are spontaneously produced with the enhancement of the photocatalytic activity in a mesoporous silica matrix by preliminary photochemical dissolution. An appropriate upshift of the conduction band of subnanometer WO3 QDs stabilized by the coverage with the surface WO bonds promotes the efficient conversion of benzene to phenol without decomposition of the product into CO2 under ultraviolet illumination.

Thermo-responsive polymers having a lower critical solution temperature (LCST) have attracted attention for biological applications such as drug delivery, diagnosis, and coating materials. In recent years, research on predicting LCST by utilizing machine learning has been conducted. However, since these methods targeted only copolymers combining specific monomer structures, they are not versatile, and multiple trials are still required to obtain new thermo-responsive polymers with the desired LCST. In this study, a prediction model for cloud point temperature (TCP) was built by a combination of materials informatics and chemical insight, named sparse modeling for small data (SpM-S) using a small dataset of polymers collected from the literature as training data. This approach created a model that is interpretable, easy to calculate, and versatile. The prediction accuracy was validated using data from different literature sources and experimental test data. The model was able to predict the TCP of polymers containing monomers not included in the dataset as well as polymers containing monomers included in the dataset. The predictive model has the potential to guide the design of new thermo-responsive polymers, and to contribute to efficient development of thermo-responsive polymers.

We constructed millimeter-wide monolayers consisting of tetragonally ordered BaTiO3 (BT) nanocubes through the liquid film formation caused by the Marangoni flow in a toluene-hexane binary liquid containing oleic acid. A thin liquid film containing BT nanocubes was overspread on a standing silicon substrate through the condensation of toluene at the advancing front after the preferential evaporation of hexane. Then, the oscillatory droplet formation like “wineglass tears” occurred on the substrate. Finally, two-dimensionally ordered BT nanocubes were observed as a stain of “wineglass tears” on the substrate after the liquid film receded through evaporation. The presence of a thin liquid film in the binary system is essential for the production of millimeter-wide monolayers on the substrate because multilayer deposition occurs without the formation of a thin liquid film in monocomponent systems. We improved the regularity of the ordered arrays of nanocubes by adjusting the liquid component and evaporation conditions.

We characterized departmental variations of the hierarchical lamellar structures of whorls, a siphonal canal, and spines of shells of a gastropod Murex pecten (Venus comb) and compared their mechanical properties. The crossed lamellae are basically composed of bundled aragonite nanorods ∼20 nm wide that are elongated along the (110) plane. The main body, including whorls and a siphonal canal, consists of four- and three-layer crossed lamellae, and thin spines comprise double- and single-layered structures including strained and distorted lamellae. The macroscopic bending strength and nanoscopic hardness of the spines were found to be greater than those of the main body of the shell. The specific strained and distorted lamellar structures are deduced to contribute to the enhanced mechanical properties of the long and thin parts.