Furfural production from xylose and bamboo powder over proton-exchanged reference clays of The Clay Science Society Japan (JCSS-3101, JCSS-3102), and a commercially available clay (K10) in water–toluene biphasic solvent was studied. The three JCSS-3101, JCSS-3102, and K10 catalysts were active for the dehydration of xylose to furfural. The activities of JCSS-3101 and JCSS-3102 were lower than that of K10. Proton-exchanging treatment enhanced the furfural yields for the three JCSS-3101, JCSS-3102, and K10 catalysts. The dehydration behaviors were almost the same and 55% yields were obtained over the three proton-exchanged clays water–toluene biphasic solvent at 413 K for 24 h.

In order to clarify the swelling mechanism in swelling clay minerals, this study attempted direct observations of clay minerals using standard transmission electron microscopy (TEM). In order to directly observe the clay mineral interlayer spaces during swelling, resin-embedded specimens were created via ultramicrotomy. The results of the observations demonstrate that the basal spacing of swelling clay minerals grows in stages as relative humidity increases, which is consistent with the results of previous studies. Partial dehydration was observed in some specimens, but the study demonstrated that even standard TEMs are capable of observing swollen clay minerals under vacuum conditions obtained through resin embedding. Furthermore, analyses of the amounts of water molecules adsorbed via energy-dispersive X-ray spectroscopy (EDS) confirms that the amount of adsorbed water molecules changes as the water molecule layer forms. This study also demonstrated that the amount of water molecules adsorbed to swelling clay minerals tends to increase in stages, whereas this amount increases continuously in non-swelling clay minerals, demonstrating a difference in the adsorption processes.

Photoluminescence (PL) of metal nanoparticles (NPs) has historically been investigated with their films, where PL is enhanced by surface plasmon resonance of the NPs themselves. In contrast, it is difficult to observe the PL in colloidal dispersion probably due to too long interparticle distance. In the present study, we observed the PL by introducing Förster resonance energy transfer from acridine orange adsorbed on saponite nanosheets, where Cu NPs were synthesized directly. In the presence of the Cu NPs, the PL spectra were dramatically changed. The PL of the Cu NPs was confirmed by temperature dependency of the PL spectra. It was also found that lifetime of AO was shortened accompanying with an additional PL component, which was ascribed to the Cu NPs. In addition, sufficient amount of the Cu NPs was distributed in the range of <20 nm from the nearest Cu NP. Therefore, it was concluded that the Cu NPs showed the PL by the energy transfer from acridine orange, which was enhanced by the surface plasmon resonance of the Cu NPs nearby.