The carbon cycle of carbonate solids (e.g., limestone) involves weathering and metamorphic events, which usually occur over millions of years. Here we show that carbonate anion intercalated layered double hydroxide (LDH), a class of hydrotalcite, undergoes an ultrarapid carbon cycle with uptake of atmospheric CO2 under ambient conditions. The use of (13)C-labeling enabled monitoring by IR spectroscopy of the dynamic exchange between initially intercalated (13)C-labeled carbonate anions and carbonate anions derived from atmospheric CO2. Exchange is promoted by conditions of low humidity with a half-life of exchange of ~24 h. Since hydrotalcite-like clay minerals exist in Nature, our finding implies that the global carbon cycle involving exchange between lithosphere and atmosphere is much more dynamic than previously thought.

To explore oxygen permeable materials, oxygen permeation properties of partially A-site substituted BaFenormalO3−δ perovskites were investigated. Ba sites in BaFenormalO3−δ were substituted with cations such as Na, Rb, Ca, Y, and La by 5%. The partial substitution with Ca, Y, and La, whose ionic radii are smaller than that of Ba, succeeded in stabilizing a cubic perovskite structure that is a highly oxygen permeable phase, as revealed by X-ray diffraction analysis. This can be explained in terms of a decrease in the tolerance factor (t) . Among the normalBa0.95normalM0.05FenormalO3−δ (M = Na, Rb, Ca, Y, and La) membranes tested, normalBa0.95normalLa0.05FenormalO3−δ showed the highest oxygen permeability at 600–930°C, owing to the stabilization of the cubic phase without the formation of impurity phases. From chemical analysis, the oxygen permeability of normalBa1−xnormalLaxFenormalO3−δ membranes was correlated with the amount of oxygen defects (δ) in the lattice. The oxygen permeation flux of normalBa0.95normalLa0.05FenormalO3−δ membrane was significantly increased by reducing its thickness. Furthermore, a normalBa0.975normalLa0.025FenormalO3−δ membrane exhibited good phase stability under He flow at elevated temperatures. The obtained results indicate the promising properties of normalBa1−xnormalLaxFenormalO3−δ membranes as a cobalt-free material that has a high oxygen permeability, good phase stability, and low cost.

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Improvements in the responses of semiconductor gas sensors and reductions in their detection limits toward volatile organic compounds (VOCs) are required in order to facilitate the simple detection of diseases, such as cancer, through human-breath analysis. In this study, we introduce a heater-switching, pulse-driven, micro gas sensor composed of a microheater and a sensor electrode fabricated with Pd-SnO-clustered nanoparticles as the sensing material. The sensor was repeatedly heated and allowed to cool by the application of voltage to the microheater; the VOC gases penetrate into the interior of the sensing layer during its unheated state. Consequently, the utility factor of the pulse-driven sensor was greater than that of a conventional, continuously heated sensor. As a result, the response of the sensor to toluene was enhanced; indeed, the sensor responded to toluene at levels of 1 ppb. In addition, according to the relationship between its response and concentration of toluene, the pulse-driven sensor in this report can detect toluene at concentrations of 200 ppt and even lower. Therefore, the combination of a pulse-driven microheater and a suitable material designed to detect toluene resulted in improved sensor response, and facilitated ppt-level toluene detection. This sensor may play a key role in the development of medical diagnoses based on human breath.

Amyloid peptides have great potential as building blocks in the creation of functional nanowires due to their natural ability to self‐assemble into nanofibrillar structures and because they can be easily modified with various functional groups. However, significant modifications of an amyloid peptide generally alter its self‐assembly property, making it difficult to construct functionalized fibrils with a desired structure and function. In this study, a very effective method to overcome this problem is demonstrated by using our structure‐controllable amyloid peptides (SCAPs) terminated with a three‐amino‐acid‐residue cap. The method consists on mixing two or more structurally related amyloid peptides with a fraction of modified SCAPs which co‐assemble into a fibril. This SCAP‐mixing method provides remarkable control over the self‐assembly process both on the small oligomers level and the macroscopic fibrils level. Furthermore, it is shown that the modified peptides imbedded in the resulting fibril can subsequently be functionalized to generate nanowires with the desired properties, highlighting the importance of this SCAP method for nanotechnology applications.

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO2 particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO2 resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (K1; for O− adsorption, K2; for O2− adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K1 and K2 in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O− and O2−. These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO2 resistive-type gas sensors in dry and wet atmospheres.

Partially Zr-substituted BaFe 1−y Zr y O 3−␦ membranes were developed as a Co-free oxygen permeable membrane. In order to stabilize the cubic perovskite structure, Fe sites in BaFeO 3−␦ were partially substituted with Zr 4+ . In the substitution range of y = 0.01-0.1, the cubic perovskite structure was stabilized even at room temperature. Among the membranes prepared, a BaFe 0.975 Zr 0.025 O 3−␦ material ͑y = 0.025͒ showed the highest oxygen permeation flux of 1.30 cm 3 ͑standard temperature pressure͒ min −1 cm −2 at 930°C under an air/He gradient. The oxygen permeation flux was higher than that of partially Ce-substituted BaFe 1−y Ce y O 3−␦ membranes reported previously. From the results obtained by chemical and scanning electron microscope analyses, it appears that the oxygen permeability for BaFe 1−y Zr y O 3−␦ membranes was well correlated with the amount of oxygen defects in the lattice as well as the grain size. In addition, the oxygen permeation flux of the BaFe 0.975 Zr 0.025 O 3−␦ membrane was significantly increased after decreasing the thickness of the membrane from 2.0 to 0.4 mm. For thin membranes ͑0.4-1.0 mm͒, the thickness dependence of the oxygen permeability deviated from the Wagner equation, suggesting that the oxygen permeation of BaFe 0.975 Zr 0.025 O 3−␦ is controlled by not only bulk diffusion of oxide ions but also their surface reactions.Membranes based on mixed conductors can selectively separate oxygen from air at high temperature. 1 The driving force of the separation is only a difference of oxygen partial pressure on both sides of membranes. Hence, the oxygen separation using mixed-conductive oxides attracts much attention as a new energy-saving oxygen separation technology. In addition, mixed-conductive membranes have been applied to another important application, called a membrane reactor that partially oxidizes methane to form hydrogen and carbon monoxide. 2 It was first reported by Teraoka et al. 3 that membranes based on La 1−x Sr x Co 1−y Fe y O 3−␦ with a cubic perovskite structure show oxygen permeability at elevated temperatures. Since then, Co-based perovskite oxides have attracted considerable interest as efficient oxygen permeation membranes. 4-8 Among them, SrCo 0.8 Fe 0.2 O 3−␦ showed high oxygen permeability, although its phase stability is low in a reducing atmosphere. 9,10 Recently, Shao et al. have reported that cubic Ba 1−x Sr x Co 1−y Fe y O 3−␦ has high oxygen permeability and good phase stability, even in a reducing atmosphere. 11,12 Among Co-based membranes, cubic SrCo 0.9 Nb 0.1 O 3−␦ 13 and SrCo 0.95 Sc 0.05 O 3−␦ 14 also show high oxygen permeability. It is known that partial substitution for A or B sites in Co-based perovskite oxide stabilizes the cubic phase at lower temperature, improving the oxygen permeability even at low temperature. 7 This makes it possible to improve the oxygen permeability through the composition control. However, membranes of this kind are not favorable for practical use because of the high cost of Co. Moreover, Co-based membranes u...

We demonstrate efficient spin injection into GaAs across an Fe3O4 electrode. Spin polarization of electrons injected into a GaAs quantum well becomes significantly large below 120 K, reaching a value of 33% at 10 K. The large spin polarization is likely due to spin filtering effect across the insulating ferrimagnetic Fe3O4 layer at the interface. The results indicate that spin filtering effect across Fe3O4 is a very promising means to enhance the spin injection efficiency into semiconductors.