Giant conductivity enhancement of ferrite insulators induced by atomic hydrogen.

Hydrogen behavior in oxides has triggered much interest for its scientific and technological importance in a wide range of research fields from novel ion conductors to astrochemistry. Here, we report a giant conductivity enhancement in ZnFe2O4 ferrite insulators to the metallic state by over eleven orders of magnitude induced by electrochemically generated atomic hydrogen at room temperature. The conductivity and the amount of incorporated hydrogen increased in an exponential function with time. An activation energy for the atomic hydrogen chemisorption was measured to be 8.23 kJ mol(-1). Quantitative kinetics correlations among the adsorption of atomic hydrogen, hydrogen incorporation and conductivity enhancement are established, based on which hydrogen incorporation process is clarified herein. We demonstrate that the hydrogen incorporation in oxides can be adjusted by manipulating the kinetic factors. These findings have implications for research into hydrogen behavior in oxides in environments containing hydrogen atoms and offer possibilities for utilizing and controlling the modifications of oxide materials induced by atomic hydrogen.

Facile synthesis of boron nitride nanotubes and improved electrical conductivity.

A layer of catalyst film on substrate is usually required during the vapor-liquid-solid (VLS) growth of one-dimensional (1D) nanomaterials. In this work, however, a novel approach for synthesizing high-purity bamboo-like boron nitride (BN) nanotubes directly on commercial stainless steel foils was demonstrated. Synthesis was realized by heating boron and zinc oxide (ZnO) powders at 1200 degrees C under a mixture gas flow of nitrogen and hydrogen. The stainless steel foils played an additional role of catalyst besides the substrate during the VLS growth of the nanotubes. In addition, the electrical conductivity of the BN nanotubes was efficiently improved in a simple way by coating with Au and Pd nanoparticles. The decorated BN nanotubes may find potential applications in catalysts, sensors and nanoelectronics.

Ube2s stabilizes ß-Catenin through K11-linked polyubiquitination to promote mesendoderm specification and colorectal cancer development.

The canonical Wnt/ß-Catenin signaling pathway is widely involved in regulating diverse biological processes. Dysregulation of the pathway results in severe consequences, such as developmental defects and malignant cancers. Here, we identified Ube2s as a novel activator of the Wnt/ß-Catenin signaling pathway. It modified ß-Catenin at K19 via K11-linked polyubiquitin chain. This modification resulted in an antagonistic effect against the destruction complex/ß-TrCP cascade-orchestrated ß-Catenin degradation. As a result, the stability of ß-Catenin was enhanced, thus promoting its cellular accumulation. Importantly, Ube2s-promoted ß-Catenin accumulation partially released the dependence on exogenous molecules for the process of embryonic stem (ES) cell differentiation into mesoendoderm lineages. Moreover, we demonstrated that UBE2S plays a critical role in determining the malignancy properties of human colorectal cancer (CRC) cells in vitro and in vivo. The findings in this study extend our mechanistic understanding of the mesoendodermal cell fate commitment, and provide UBE2S as a putative target for human CRC therapy.

Hydrogen Impurity Defects in Rutile TiO2.

Hydrogen-related defects play crucial roles in determining physical properties of their host oxides. In this work, we report our systematic experimental and theoretical (based on density functional theory) studies of the defect states formed in hydrogenated-rutile TiO2 in gaseous H2 and atomic H. In gas-hydrogenated TiO2, the incorporated hydrogen tends to occupy the oxygen vacancy site and negatively charged. The incorporated hydrogen takes the interstitial position in atom-hydrogenated TiO2, forming a weak O-H bond with the closest oxygen ion, and becomes positive. Both states of hydrogen affect the electronic structure of TiO2 mainly through changes of Ti 3d and O 2p states instead of the direct contributions of hydrogen. The resulted electronic structures of the hydrogenated TiO2 are manifested in modifications of the electrical and optical properties that will be useful for the design of new materials capable for green energy economy.

Facile Synthesis of Ternary Boron Carbonitride Nanotubes.

In this study, a novel and facile approach for the synthesis of ternary boron carbonitride (B-C-N) nanotubes was reported. Growth occurred by heating simple starting materials of boron powder, zinc oxide powder, and ethanol absolute at 1150 degrees C under a mixture gas flow of nitrogen and hydrogen. As substrate, commercial stainless steel foil with a typical thickness of 0.05 mm played an additional role of catalyst during the growth of nanotubes. The nanotubes were characterized by SEM, TEM, EDX, and EELS. The results indicate that the synthesized B-C-N nanotubes exhibit a bamboo-like morphology and B, C, and N elements are homogeneously distributed in the nanotubes. A catalyzed vapor-liquid-solid (VLS) mechanism was proposed for the growth of the nanotubes.