In this study, the influence of the negative charge distribution and the locations of Na+ ions on ionic conductivity of Na-micas was investigated. The locations of Na+ ions in as-prepared Na-micas and heated Na-micas at 700°C were determined in details using X-ray diffraction analyzer, Fourier transform infrared spectrophotometer, 23Na magic angle spinning nuclear magnetic resonance and X-ray photoelectron spectroscopy. As the results, four kinds of Na+ ions, such as Na+ ions induced into vacant sites in the octahedral sheets, hydrated Na+ ions in the interlayer, dehydrated Na+ ions surrounded by six basal oxygens and Na+ ions drawn into the inside of the ditrigonal hole, were found in Na-micas. Ionic conductivities of the heated Na-micas were measured at 400 to 600°C by an alternating current four-probe method. Among the Na-micas, Na-taeniolite showed the maximum ionic conductivity, which was 6.61×10−4 S/cm at 600°C. Following relationships were obtained from the results. The hydrated Na+ ions in the interlayer and the dehydrated Na+ ions surrounded by six basal oxygens contributed to the ionic conductivity of Na-mica, while the octahedral Na+ ions and the Na+ ions drawn into the inside of the ditrigonal hole hardly contribute to the ionic conductivity. In addition, because tetrasilisic type mica had weaker electrostatic bonding force between layer and interlayer cation than trisilisic type mica, the Na+ ions of tetrasilisic type mica were migrated more easily than that of trisilisic type mica.
Uronic acids are common organic molecules that are released from microbes and plants in the earth’s surface environments. To evaluate the effect of uronic acids on the precipitation rate and polymorphism of calcium carbonate (CaCO3) minerals, precipitation experiments of CaCO3 minerals were performed in systems containing glucuronic acid and galacturonic acid using the batch method with a 100 mL solution at 25°C. Each solution contained 5.0 mM Ca2+ and Mg2+, and 20.0 mM HCO3 ions with 0.00, 0.01, 0.05, 0.1, 0.5, and 1.0 mM of glucuronic acid or galacturonic acid. Additionally, the adsorption experiments with these uronic acids were performed on the surface of calcite and aragonite to confirm their adsorption affinity for the surfaces of CaCO3 minerals. The results showed that both uronic acids inhibited the precipitation of CaCO3 minerals with increasing the concentrations. The inhibition effect of galacturonic acid was much greater than that of glucuronic acid. In addition, only aragonite was formed as a stable polymorph in solutions containing no uronic acid due to the effect of Mg2+ ions. However, galacturonic acid inhibited the formation of aragonite and enhanced the formation of calcite as a stable polymorph of CaCO3 minerals, whereas glucuronic acid showed no significant effect on the polymorphism at concentrations below 1.0 mM. These adsorption experiments revealed that galacturonic acid exhibited much greater adsorption on both surfaces of aragonite and calcite compared to glucuronic acid. Consequently, the extent of the effect on the precipitation rate and polymorphism is consistent with the adsorption affinity of uronic acids for the surfaces of CaCO3 minerals.
Aflatoxin B1 (AfB1) is one of the main contaminant of grains such as corn and wheat, causing damage to livestock through ingestion of contaminated feed. Recently, various clays have been added to the feed to adsorb mycotoxins and to prevent mycotoxicosis of animals. However, the effect of kind of clays is still unclear. In this study, several kinds of natural clays such as bentonite and sepiolite, as well as the synthetic two-dimensional talc as a reference, were tested as an adsorbent for AfB1 in aqueous solutions. All of the clays used here was found to have high adsorption performance for AfB1. Especially, five kinds of the bentonite samples indicated the larger adsorption capacity and the faster adsorption rate of AfB1 in spite of their relatively lower specific surface area. The adsorption capacity of the sepiolite sample was almost similar to the bentonite samples, but the adsorption rate was somewhat smaller because of its intrinsic smaller pore structure. Moreover, the adsorption capacity of these clay for AfB1 was hardly influenced by the solution pH of 3–9 and temperature of 25–40°C, and the desorption of AfB1 from these clay samples in water was almost negligible. In these cases, AfB1 molecules are thought to be captured by the chelating of two carbonyl groups with metal cation at the destruction face of the clay basal layer. In conclusion, these natural and acid-treated clays can be used as the practical adsorbent to prevent mycotoxicosis of animals.
