In order to elucidate the heat treatment effects on water vapor adsorption properties of Noto-diatomaceous earth (Noto-DE), the specific surface area (SSA) was measured with N2 and H2O, and pore size distribution and water vapor adsorption of the samples were also measured. Particles ＞75 µm and ＜ 2 µm in size were separated from the samples of Noto-DE and they were calcined at various temperatures up to 1,000°C. Both particles ＞75 µm and ＜2 µm showed that the SSA values measured with H2O were larger than those with N2. This may be caused by the chemical adsorption action on silanol radical of diatomaceous shell and the interlayer of clay minerals. Concerning samples after particle-size classification, fraction having particle size not greater than 2 µm showed the most water vapor adsorption. This result indicates that the clay minerals that account for ca. 40% of Noto-DE have a great influence on water vapor adsorption properties. Furthermore the reason why water vapor adsorption of Noto-DE decreased sharply at heat treatment above 800°C may be due to change of structure of montmorillonite. Therefore it was found that the changes in the water vapor adsorption properties of Noto-DE by heating were caused by the changes in the crystalline structure of montmorillonite.
Montmorillonite clay plays an important role as a key component in bentonite buffer materials used for the safe geological disposal of radioactive waste. Molecular dynamics (MD) simulations were performed to investigate the physical properties of water and relevant cations within the montmorillonite interlayer nanopores. We discuss the application of these results to a diffusion model in compacted montmorillonite. The swelling behavior and hydration states were evaluated as functions of interlayer cations (Na, K, Cs, Ca and Sr) and layer charge (0.2–0.75 e/unit cell) by comparing the basal spacing, immersion enthalpy and partial molar volumes. These were controlled by the hydration properties of the interlayer cations and by electrostatic interaction with the montmorillonite layer. The diffusion coefficients of water and cations in the interlayer nanopores decreased compared to those in bulk water and became close to those in bulk water as the basal spacing increased. The diffusion behavior was correlated to the hydration energy and hydration radius of the interlayer cations. The viscosity coefficients of the interlayer water, estimated from the common relationship between diffusion and viscosity coefficients in bulk water, indicated a significant viscoelectric effect for both the 1- and 2-layer hydration states which increased in montmorillonites with higher layer charge. These trends derived from the MD calculations are consistent with existing measured data and previous MD simulations. In addition, the parameters related to viscoelectric effect used in the diffusion model were refined, based on comparison between the MD simulations and measurements. This series of MD calculations provides an atomic level understanding for the development and improvement for the diffusion model of compacted montmorillonite.
Localized surface plasmon resonance of Au, Ag and Cu nanoparticles (NPs) has attracted tremendous attention due to their visible light absorption and enhancement of the local electric field. Their syntheses by using protectants such as thiols and polymers have been investigated deeply, and numerous studies on morphological controls have ever been reported. In contrast, direct syntheses of the metal NPs on supports have also been important for an application to catalysts. In this point of view, layered compounds seem to be one of the most promising supports because of their large specific surface area and adsorption property. Indeed, syntheses of the metal NPs have been reported in the interlayer spaces of the layered compounds or on the nanosheets obtained by exfoliation. However, the synthetic methods have not been established yet. Here, we briefly introduce our recent studies on hybridization of the Au, Ag or Cu NPs with layered clay minerals or layered titanates, performed independently. The Au NPs were synthesized on montmorillonite nanosheets both by chemical and photoreduction methods, and nanoscopic homogeneity was found to be important for the diameter control of the Au NPs. The interlayer space of titania nanosheet thin film was also found to be effective to produce anisotropic Ag NPs, whose surface plasmon band was observed in the near-infrared region. Not only Ag＋ but also Ag2O was useful to obtain the Ag NPs by using the photocatalytic titania nanosheets as the supports. The obtained nanocomposite showed peculiar photochromism. Similar to the nanosheets as the support, assembly of the nanosheets was used to synthesize diameter-controlled Cu NPs, which showed efficient photoinduced electron transfer. We believe that the nanocomposites described above will contribute to investigation and development of novel functional materials.