Graphene oxide membranes-partially oxidized, stacked sheets of graphene-can provide ultrathin, high-flux and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution. These materials have shown potential in a variety of applications, including water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike the pores of carbon nanotube membranes, which have fixed sizes, the pores of graphene oxide membranes-that is, the interlayer spacing between graphene oxide sheets (a sheet is a single flake inside the membrane)-are of variable size. Furthermore, it is difficult to reduce the interlayer spacing sufficiently to exclude small ions and to maintain this spacing against the tendency of graphene oxide membranes to swell when immersed in aqueous solution. These challenges hinder the potential ion filtration applications of graphene oxide membranes. Here we demonstrate cationic control of the interlayer spacing of graphene oxide membranes with ångström precision using K, Na, Ca, Li or Mg ions. Moreover, membrane spacings controlled by one type of cation can efficiently and selectively exclude other cations that have larger hydrated volumes. First-principles calculations and ultraviolet absorption spectroscopy reveal that the location of the most stable cation adsorption is where oxide groups and aromatic rings coexist. Previous density functional theory computations show that other cations (Fe, Co, Cu, Cd, Cr and Pb) should have a much stronger cation-π interaction with the graphene sheet than Na has, suggesting that other ions could be used to produce a wider range of interlayer spacings.

NaCl in a 1:1 stoichiometry is the only known stable form of the Na-Cl crystal under ambient conditions, and non-1:1 Na-Cl species can only form under extreme conditions, such as high pressures. Here we report the direct observation, under ambient conditions, of NaCl and NaCl as two-dimensional (2D) Na-Cl crystals, together with regular NaCl, on reduced graphene oxide membranes and on the surfaces of natural graphite powders from salt solutions far below the saturated concentration. Molecular dynamics and density functional theory calculations suggest that this unconventional crystallization process originates from the cation-π interaction between the ions and the π-conjugated system in the graphitic surface, which promotes the ion-surface adsorption. The strong Na-π interaction and charge transfer lead to stoichiometries with an excess of Na. With unique electron and spin distributions and bonding, the resulting 2D crystals may have unusual electronic, magnetic, optical and mechanical properties.

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Developing efficient cathode catalysts can largely promote the application of Li‐O2 batteries (LOBs). In this work, the core‐shell MoS2−x@CNTs composite is synthesized via a hydrothermal method with annealing and NaBH4 reduction post‐processing, of which the defective MoS2 nanoflakes are homogeneously coated on the 3D carbon nanotube (CNT) webs. It is found that it delivers superior bifunctional catalytic activities toward both oxygen reduction and evolution reactions for LOBs. On the one hand, the charge re‐distribution on MoS2 nanoflakes with sulfur vacancies can be effectively constructed by the surface engineering strategy, remarkably boosting the kinetics of Li‐O2 catalysis. On the other hand, the conductive and high surface area CNT network can facilitate mass transfer and provide enough free space for composite cathodes, accommodating the volume changes caused by the reversible formation and decomposition of discharge products during cycling. More importantly, the unique core‐shell architecture can not only enable fully covering of defective MoS2 nanoflakes on CNT surfaces to avoid the contact between CNTs and electrolyte, distinctly suppressing side reactions, but also realize the exposure of more active sites to fulfill their catalytic properties. This work provides an insightful investigation on advanced catalysts and holds great potential for catalyst structural engineering in LOBs.

Consider n i.i.d. random vectors on R 2 , with unknown, common distribution function F . Under a sharpening of the extreme value condition on F , we derive a weighted approximation of the corresponding tail copula process. Then we construct a test to check whether the extreme value condition holds by comparing two estimators of the limiting extreme value distribution, one obtained from the tail copula process and the other obtained by first estimating the spectral measure which is then used as a building block for the limiting extreme value distribution. We derive the limiting distribution of the test statistic from the aforementioned weighted approximation. This limiting distribution contains unknown functional parameters. Therefore, we show that a version with estimated parameters converges weakly to the true limiting distribution. Based on this result, the finite sample properties of our testing procedure are investigated through a simulation study. A real data application is also presented.

The proapoptotic function of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) phosphatase has been linked to its capacity to antagonize the phosphatidylinositol-3-kinase-Akt signaling pathway. Previous studies have shown that the Forkhead transcriptional factor (FOXO3a) is a critical effector of the PTEN-mediated tumor suppressor. However, whether the PTEN-AktFOXO3a pathway is involved in neuronal apoptosis in developing rat brain after hypoxia-ischemia (HI) is unclear. In this study, we generated an HI model using postnatal day 10 rats. Immunohistochemistry and western blot were used to detect the expression of total and phosphorylated PTEN, Akt, and FOXO3a, as well as its target gene Bim. We found that dephosphorylation of PTEN was accompanied by dephosphorylation of Akt and FOXO3a, which induced FOXO3a translocation into the nucleus and upregulated the expression of Bim. Furthermore, we found that PTEN inhibition by bisperoxovanadium significantly increased the phosphorylation of Akt and FOXO3a, decreased the nuclear translocation of FOXO3a, and inhibited Bim expression after HI. Moreover, the downregulation of Bim caused by PTEN inhibition attenuated cellular apoptosis in developing rat brain. Our findings suggest that the PTEN-Akt-FOXO3a pathway is involved in neuronal apoptosis in neonatal rat brain after HI. Agents targeting PTEN may offer a promise to rescue neurons from HI brain damage.

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