Na-kenyaite, a layered silicate, was synthesized via the hydrothermal method at 190 °C for 24 h using amorphous SiO₂ blocks as a starting material. Changes in the thermal structure of Na-kenyaite were investigated using the in situ high-temperature synchrotron X-ray diffraction data. Na-kenyaite was dehydrated at 200 °C, and its crystal structure was maintained from 200 to 700 °C despite its low crystallinity. It finally decomposed and crystallized to cristobalite via α-quartz. Na-kenyaite was ion-exchanged with Ag⁺ and Cu²⁺ ions in different ratios (Ag/Si = 0.01–0.077 and Cu/Si = 0.009–0.044), and the antibacterial properties of the ion-exchanged compounds were evaluated using gram-negative [Escherichia coli (E. coli)] and gram-positive [Staphylococcus aureus (S. aureus)] bacteria. Ion-exchanged compounds exhibited an increasing bactericidal effect when the ion-exchange ratios of the compounds increased owing to the release of metal ions with antibacterial properties from the host material. The antibacterial activity of the ion-exchanged compounds was compared based on the relative antibacterial activity, calculated using the inhibition zone obtained after two days of incubation. Cu-kenyaite exhibited better antibacterial activity than Ag-kenyaite against E. coli and S. aureus.

Zeolites are key materials in chemical industry exploited for their microporous structure. The control of the Si/Al ratio is one of the primary topics in zeolite science, especially for zeolites with 8-rings as their largest pores (small-pore zeolites), when considering their uses in catalysis and other applications. Although the direct synthesis method often yielded small-pore zeolites with a limited Si/Al ratio, our group successfully demonstrated post-synthetic dealumination in the presence of organic pore fillers. So far several types of small-pore zeolites, including AEI and AFX zeolites, could be dealuminated by acid treatment, still RHO zeolite loses its crystallinity after acid treatment, requiring another strategy for successful dealumination. In this work, successful dealumination of RHO zeolite with preserved crystallinity is demonstrated by acid treatment followed by post-synthesis recrystallization. The decrease in crystallinity during acid treatment is recovered by crystallization in the presence of a saturated silicate solution, and the final Si/Al ratio exceeded 7. When 18-crown-6 ether is added to the treatment solution as a pore-filling agent to avoid the occlusion of excess inorganic cations into the zeolite pores, the final bulk Si/Al ratio is 7.5. The relative crystallinity and micropore volume are 83 % and 0.27 cm³ g⁻¹, respectively, showing its high crystallinity. The resulting RHO zeolite is expected to show a superior hydrothermal stability during catalytic application such as selective catalytic reduction of nitrogen oxides.

Platinum nanoparticles (PtNPs) were prepared using a continuous-flow precision synthesis system with hydrogen hexachloroplatinate(IV) hexahydrate and methanol as the metal source and reductant, respectively. The effects of the synthesis conditions, including the reaction temperature and flow tube length, on the size, morphology, and yield of PtNPs were investigated. The X-ray diffraction patterns of the obtained samples revealed the formation of Pt metal crystallites. Transmission electron microscopy suggested that the particle size and morphology of the PtNPs did not change when the reaction temperature and flow tube length were varied, and the PtNPs were spherical with a diameter of ∼3 nm. Conversely, the yield increased considerably with increasing reaction temperature and flow tube length, and the sample prepared using a 5-m flow tube at 140 °C was ∼51 %. Thus, this system can continuously synthesize PtNPs within a few minutes.

Nonstoichiometric rare-earth oxyfluorides (RO_1−xF_1+2x) were synthesized and the relationship between the crystalline phase and fluoride-ion-conducting properties were investigated. In the case of stoichiometric ROF (x = 0.0) except for YbOF, a trigonal structure (R3m) was formed, in which the RO₄F₄ unit was distorted as the ionic radius of R³⁺ decreased. The introduction of F⁻ ions into the lanthanum oxyfluoride (LaOF) structure, which initially had the rectangular RO₄F₄ unit, resulted in a transformation to the tetragonal P4/nmm phase. However, in the case of nonstoichiometric RO_1−xF_1+2x with an increased distortion in the RO₄F₄ unit compared to the stoichiometric ROF (x = 0.0), lower symmetric orthorhombic Pmmn and Abm2 phases were obtained. The electrical conductivity of the RO_1−xF_1+2x solids is significantly influenced by their structural symmetry, and the LaO_1−xF_1+2x solid having the most symmetric RO₄F₄ units in the structure exhibited the highest ion conductivity.

Hollow silica particles (HSPs) were prepared using calcium carbonate (CaCO₃) templates coated with silica layers via chemical vapor deposition (CVD), and the effects of the deposition duration on the microstructure and pore structure of the HSPs were investigated. The silica layers were deposited on the CaCO₃ template particles by a rotary CVD technique at a deposition temperature of 540 °C. The amount and thickness of silica layers in the resultant silica-coated CaCO₃ templates prepared with deposition time of 60–240 min were estimated as 12.2–16.6 wt.% and 17.4–22.9 nm, respectively, by thermogravimetry. HSPs were formed by removing of the templates by acid treatment, which had 10–30 nm thick silica shells with angular morphologies that were inherited from those of the templates. The specific surface area of the HSPs increased from 75 to 466 m²/g as the deposition time decreased from 240 to 60 min. The HSPs using the silica-coated template prepared at 60 min involved a large number of micropores (223 m²/g) as well as bursts and holes that were formed by the removal process of the templates, whereas no micropores were formed in the HSPs when the deposition duration was prolonged to 120–240 min.

The flash sintering method has garnered attention for its ability to significantly accelerate the densification rate of ceramic green compact through the generation of an electric power spike under an electric field exceeding a defined threshold. In order to amass foundational knowledge about the phenomenon that results from an electric field during flash sintering via a voltage-to-current protocol, the dihedral angles of grain boundaries were surveyed in flash-treated pre-sintered fully stabilized zirconia polycrystal. The flash treatment resulted in a reduction of the grain boundary dihedral angle for grain boundaries that are approximately perpendicular to the direction of the electric field. The reduction in the dihedral angle is possibly attributed to a reduction in surface energy which can be observed through the formation of sinuous pores during flash sintering.