Strengthening mechanisms of highly textured Cu/Co and Ag/Al nanolayers with high density twins and stacking faults

Metallic nanolayers have attracted increasing attention as they provide unique opportunity to investigate the influence of layer interfaces on mechanical properties of metallic nanocomposites. High strength is often achieved at small (several nm) individual layer thickness (h). Recently, we discovered high-density stacking faults in FCC Co in highly (100) textured Cu/Co multilayers. In contrast in (111) textured Cu/Co nanolayers, Co remained its stable HCP structure at large h. The two Cu/Co systems have very different size dependent strengthening behavior. HCP Cu/Co has much greater peak strength than FCC Cu/Co. The large discrepancy in their strengthening mechanisms is discussed and compared to those of highly textured Cu/Ni multilayer systems. In another highly textured nanolayers system, Ag/Al, epitaxial interfaces were observed across various h (1‑200 nm). High-density nanotwins and stacking faults appear in both Ag and Al layers, and stacking fault density in Al increases sharply with decreasing h. At smaller h, hardness of Ag/Al nanolayers increases monotonically and no softening was observed. These studies allow us to investigate the influence of layer interfaces, stacking faults and nanotwins on strengthening mechanisms of metallic nanolayers. This research is funded by DOE–OBES

Fe/Co-based Bimetallic MOF-derived Co3Fe7@NCNTFs Bifunctional Electrocatalyst for High-Efficiency Overall Water Splitting

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrocatalytic water splitting to produce hydrogen and oxygen is regarded as one of the most promising methods to generate clean and sustainable energy for replacing fossil fuels. However, the design and development of an efficient bifunctional catalyst for simultaneous generation of hydrogen and oxygen remains extremely challenging yet is critical for the practical implementation of water electrolysis. Here, we report a facile method to fabricate novel N-doped carbon nanotube frameworks (NCNTFs) by the pyrolysis of a bimetallic metal organic framework (MIL-88-Fe/Co). The resultant electrocatalyst, Co3Fe7@NCNTFs, exhibits excellent oxygen evolution reaction (OER) activity, achieving 10 mA/cm2 at a low overpotential of just 264 mV in 1 M KOH solution, and 197 mV for the hydrogen evolution reaction. The high electrocatalytic activity arises from the synergistic effect between the chemistry of the Co3Fe7 and the NCNTs coupled to the novel framework structure. The remarkable electrocatalytic performance of our bifunctional electrocatalyst provides a promising pathway to high-performance overall water splitting and electrochemical energy devices

Lanostane Triterpenoids and Ergostane Steroids from <i>Ganoderma luteomarginatum</i> and Their Cytotoxicity

Macrofungus Ganoderma luteomarginatum is one of the main species of Ganoderma fungi distributed in Hainan province of China, the fruiting bodies of which have been widely used in folk as a healthy food to prevent tumors. To explore the potential cytotoxic constituents from G. luteomarginatum, the phytochemical investigation on the ethyl acetate soluble fraction of 95% ethanolic extract from the fruiting bodies of this fungus led to the isolation of twenty-six lanostane triterpenoids (1–26), including three undescribed ones (1–3), together with eight ergostane steroids (27–34). The structures of three new lanostane triterpenoids were elucidated as lanosta-7,9(11)-dien-3β-acetyloxy-24,25-diol (1), lanosta-7,9(11)-dien-3-oxo-24,26-diol-25-methoxy (2), and lanosta-8,20(22)-dien-3,11,23-trioxo-7β,15β-diol-26-oic acid methyl ester (3) by the analysis of 1D, 2D NMR, and HRESIMS spectroscopic data. All isolates were assayed for their cytotoxic activities using three human cancer cell lines (K562, BEL-7402, and SGC-7901) and seven lanostane triterpenoids (1, 2, 7, 13, 18, 22, and 24), and one ergostane steroid (34) showed definite cytotoxicity with IC50 values that ranged from 6.64 to 47.63 μg/mL. Among these cytotoxic lanostane triterpenoids, compounds 2 and 13 showed general cytotoxicity against three human cancer cell lines, while compounds 1 and 18 exhibited significant selective cytotoxicity against K562 cells with IC50 values of 8.59 and 8.82 μg/mL, respectively. Furthermore, the preliminary structure–cytotoxicity relationships was proposed

Manipulation of domain wall mobility by oxygen vacancy ordering in multiferroic YMnO3

The mobility of the ferroelectric domain phases and the local conductivity of ferroelectric domain walls in multiferroic YMnO3 crystals grown in air and reduced atmosphere were studied by piezoresponse force microscopy (PFM), tip-enhanced Raman spectroscopy (TERS) and conductive atomic force microscopy (CAFM). Oxygen vacancies were found to reduce the strength of 4d–2p (Y3+–O2−) hybridization and structural trimerization distortion, leading to the disappearance of the six wedge-shaped ferroelectric domain phases in oxygen deficient YMnO3−δ crystals. We observed anisotropic domain wall motion such that the wedge-shaped domain configuration joined at one point could be changed to the stripe domain configuration by applying high electric fields in oxygen deficient YMnO3−δ single crystals. The local conductivity of the domain walls increased significantly in poled YMnO3−δ single crystals. The straight conductive domain walls in YMnO3−δ, instead of the twisted insulating ones in the stoichiometric crystal, are induced by the ordered oxygen vacancies which are verified by TERS measurements

Band-gap engineering of BiOCl with oxygen vacancies for efficient photooxidation properties under visible-light irradiation

It remains a great challenge to understand the role of oxygen vacancies in determining the photooxidation properties of semiconductors under visible-light irradiation. Herein, BiOCl with oxygen vacancies is proposed as an excellent model to study the relationship between oxygen vacancies and photooxidation properties. BiOCl nanosheets with abundant oxygen vacancies are synthesized via a facile solvothermal route. Theoretical and experimental results reveal that after the introduction of oxygen vacancies, a new electron donor level appears in the band gap of BiOCl, extending the absorption from the ultraviolet to the visible regime. As expected, BiOCl nanosheets with oxygen vacancies exhibit visible-light-driven photocatalytic activity towards oxygen evolution. In addition, BiOCl with abundant oxygen vacancies exhibits a higher visible-light photocurrent and more efficient photoinduced charge separation and transportation than BiOCl with a small number of oxygen vacancies. The introduction of oxygen vacancies on the surfaces of semiconductors provides a promising way to improve the visible-light photooxidation activity of photocatalysts