Published papers

This work clarified the effects of self-assembly of perovskite cesium lead bromide (CsPbBr3) nanocubes (NCs) covered with didodecyldimethyl ammonium bromide (DDAB) on photoluminescence (PL) properties. Although the PL intensity of isolated NCs was weakened in the solid state even under inert conditions, the quantum yield of PL (PLQY) and the photostability of DDAB-covered NCs were drastically improved by the formation of two-dimensional (2D) ordered arrays on a substrate. The PLQY of the 2D arrays increased to ca. 60% by initial excitation illumination at 468 nm and was maintained for over 4000 h. The improved PL properties are attributable to the fixation of the surface ligand around the NCs in the specific ordered arrays.

Exfoliated nanosheets have attracted considerable interest as two-dimensional (2D) building blocks. In general, the yield, size, and size distribution of the exfoliated nanosheets cannot be easily controlled or predicted because of the complexity in the processes. Our group studied the prediction models of the yield, size, and size distribution based on the small experimental data available. Sparse modeling for small data (SpM-S) combining machine learning (ML) and chemical insight was used for the construction of predictors. In SpM-S, the weight diagram visualizing the significance of explanatory variables plays an important role in variable selection to construct the models. However, the processes of variable selection were not validated in a data-scientific manner. In the present work, the significance of data size, visualization method, and chemical insight for variable selection was studied to validate the processes of model construction. The data size had a lower limit to extract appropriate descriptors. The weight diagram had an appropriate visualizing range for variable selection. Chemical insight as domain knowledge supplemented the limitation caused by the data size. These studies indicated that SpM-S can be applied to construct predictors, straightforward linear regression models, for the controlled syntheses of other 2D materials, even based on small data.

We designed CaCO3 films comprised of aragonite nanorods by mimicking the microstructure and the formation process of the calcareous skeleton of a stony coral in the sea. Hierarchically structured calcareous frameworks are produced from the center of calcification (COC) under alkaline conditions in the organism. In the first step, a seed layer consisting of crystalline nanoparticles was produced as an artificial COC on a polyvinyl alcohol sheet in a solution containing Ca2+ ions, polyacrylic acid, and a biogenic polyamine, such as putrescine, through the gradual absorption of atmospheric CO2. In the second step, aragonite nanorods grew on the artificial COC in the mother liquid obtained by mixing a putrescine solution saturated with CO2 and a CaCl2 solution containing Mg2+ and alginate. Finally, we obtained a dense, homogeneous film consisting of aragonite nanorods similar to the coral skeleton through the fixation of CO2

Organic electrode-active materials are important for the development of metal-free, high-performance energy storage devices without resource consumption. Further exploration at an accelerated pace is necessary to find new compounds that exhibit high performances in an infinite number of organic molecules. Exploration based on professional experience, research expertise and intuition has its limitations. In the present work, potential compounds for organic anode active materials are efficiently found in the natural products of flower scents. A total of 65 potential compounds with conjugated moieties are extracted from the original data by the initial screening. Prior to the experiments, eight compounds are selected as candidates using the capacity predictor. Two compounds, 1,4-dichlorobenzene and 6-methyl-2-pyridinecarboxyaldehyde, actually exhibit higher specific capacities of 532 and 293 mA h g−1 with subtraction of the capacity originating from conductive carbon at the current density of 100 mA g−1. Polymerizable structural analogues are found from further exploration. The polymer of pyrrole-2-carboxyaldehye as an analogue exhibits a specific capacity of 934 mA h g−1 at 100 mA g−1. Thus, a couple of new potential anode active materials have been successfully found by efficient exploration using the capacity predictor in natural products.

Millimeter-scale mesocrystals and cross-lamellae mimicking the nanostructure of seashells were produced on a substrate through the three-dimensionally oriented assembly of c-axis-elongated calcite nanorods ∼50 nm wide and ∼500-1000 nm long by combining arrangement with evaporation-driven capillary force and alignment under an intense magnetic field.

Biomimetic strained SrSO4 crystals were produced through a nonclassical pathway involving fiber-by-fiber accumulation with poly(acrylic acid) in an aqueous solution system. Polymer-stabilized fibrous hydrate crystals 20-40 nm wide and several micrometers long were formed in the initial stage. Spindle-shaped microrods of SrSO4 were then constructed by oriented attachment of the hydrous fibrils and subsequent dehydration. The strained structure of the anhydrous SrSO4 crystals is similar to biogenic SrSO4 spines of acantharian species, a marine unicellular holoplanktonic protist.

Calcitic spines ∼1 μm in diameter are projecting from a trochospiral test of a spinose planktonic foraminifer. According to electron diffraction, Raman spectra, and detailed electron microscope observation, the spines were found to be a single-crystal-like calcite that has a nanogranular texture containing microstrain. An organic envelope protects the biogenic calcite against dissolution in water. Their unique mechanical and chemical properties are ascribed to the specific micro- and nanoscopic structures. This journal is