Individual Titanate Nanoribbons Studied by 3D-Resolved Polarization Dependent X‑ray Absorption Spectra Measured with Scanning Transmission X‑ray Microscopy

Polarization dependent X-ray absorption spectroscopy (XAS) is a powerful probe of the anisotropic electronic structure of bulk single crystals, but its application to nanostructured samples is challenging. Here we describe a method for obtaining linearly polarized XAS spectra along three orthogonal axes of an individual nano-object using scanning transmission X-ray microscopy (STXM). The technique is applied to a single sodium titanate nanoribbon [(Na,H)Ti NR]. Significant linear dichroism is observed at both the Ti 2p and O 1s edges. The experimental results are compared with first-principles calculations; good agreement is achieved. The spectral changes among the three axes are attributed to the anisotropic Ti–O bonding of the various Ti and O sites in the monoclinic crystal structure of the nanoribbon. The methodology for 3D dichroic STXM measurements developed in this study is a powerful way to investigate the anisotropic geometric and electronic structure of nanomaterials

Petrology and geochronology of ultrahigh-pressure granitic gneiss from South Dulan, North Qaidam belt, NW China

<div><p>abstract</p><p>An integrated study including petrography, mineral chemistry, metamorphic P–T path modelling, and zircon U–Pb dating was conducted on a granitic gneiss and enclosed eclogite from South Dulan, North Qaidam UHP (ultrahigh-pressure) belt. The result shows that the granitic gneiss underwent a clockwise P–T path with a peak-P stage at 655–745°C, 30–34 kbar, and a subsequent peak-T stage at 815–870°C, 14–18 kbar, which is similar to the P–T estimates reported for coesite-bearing continental-type eclogites in this region. The enclosed eclogite resembles an olivine–pyroxene-rich cumulate in Qaidam block. It has a similar prograde P–T path with the country gneiss and experienced a peak-P stage of 682–748°C at 27–34 kbar. Zircon U–Pb dating yields an eclogite-facies metamorphic age of 447 ± 2 Ma for the granitic gneiss and 445 ± 6 Ma for the enclosed eclogite. These ages agree with metamorphic ages obtained from paragneisses (427–439 Ma), coesite-bearing continental-type eclogites (430–451 Ma), and UHPM (ultrahigh-pressure metamorphic) oceanic crust–mantle sequence (440–445 Ma) from South Dulan, as well as UHP eclogites, garnet peridotite, and gneisses from other units (460–420 Ma) within this belt reported by others. Similar metamorphic ages as well as P–T evolution documented in gneisses and intercalated eclogites imply that both rocks experienced a coeval UHP event. Summarizing all the published geochronology data, we argue that the North Qaidam UHP belt was mainly formed by continental deep subduction at ~460 to ~420 Ma. The UHPM oceanic crust-mantle sequence in South Dulan may represent oceanic lithosphere in the transition zone between oceanic and continental crust, which was dragged upward by the exhumed continental rocks after break-off of the dense oceanic crust.</p></div

X-ray Absorption Spectroscopy and Magnetism of Synthetic Greigite and Greigite Magnetosomes in Magnetotactic Bacteria

<p>Scanning transmission X-ray microscopy at the Fe 2p (L_2,3), O1s, C1s, and S2p edges was used to study greigite magnetosomes and other cellular content of a magnetotactic bacterium known as a multicellular magnetotactic prokaryote (MMP). X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) spectra of greigite (Fe₃S₄) nanoparticles, synthesized via a hydrothermal method, were measured. Although XAS of the synthetic greigite nanoparticles and biotic magnetosome crystals in MMPs are slightly different due to partial oxidation of the MMP greigite, the XMCD spectra of the two materials are in good agreement. The Fe 2p XAS and XMCD spectra of Fe₃S₄ are quite different from those of its oxygen analog, magnetite (Fe₃O₄), suggesting Fe₃S₄ has a different electronic and magnetic structure than Fe₃O₄ despite having the same crystal structure. Sulfate and sulfide species were also identified in MMPs, both of which are likely involved in sulfur metabolism.</p

High-Resolution Imaging of Polymer Electrolyte Membrane Fuel Cell Cathode Layers by Soft X‑ray Spectro-Ptychography

Polymer electrolyte membrane fuel cells (PEMFCs) are a promising and sustainable alternative to internal combustion engines for automotive applications. Polymeric perfluorosulfonic acid (PFSA) plays a key role in PEMFCs as a proton conductor in the anode and cathode catalyst layers and in the electrolyte membrane. In this study, spectroscopic scanning coherent diffraction imaging (spectro-ptychography) and spectro-ptychographic tomography were used to quantitatively image PFSA ionomers in PEMFC cathodes in both two and three dimensions. We verify that soft X-ray ptychography gives significant spatial resolution improvement on soft matter polymeric materials. A two-dimensional spatial resolution of better than 15 nm was achieved. With better detectors and brighter and more coherent X-ray beams, radiation-sensitive PFSA ionomers will be visualized with acceptable levels of chemical and structural modification. This work is a step toward visualization of ionomers in PEMFC cathodes at high spatial resolution (presently sub-15 nm, but ultimately below 10 nm), which will be transformative with respect to optimization of PEMFCs for automotive use

High-Resolution Imaging of Polymer Electrolyte Membrane Fuel Cell Cathode Layers by Soft X‑ray Spectro-Ptychography

Polymer electrolyte membrane fuel cells (PEMFCs) are a promising and sustainable alternative to internal combustion engines for automotive applications. Polymeric perfluorosulfonic acid (PFSA) plays a key role in PEMFCs as a proton conductor in the anode and cathode catalyst layers and in the electrolyte membrane. In this study, spectroscopic scanning coherent diffraction imaging (spectro-ptychography) and spectro-ptychographic tomography were used to quantitatively image PFSA ionomers in PEMFC cathodes in both two and three dimensions. We verify that soft X-ray ptychography gives significant spatial resolution improvement on soft matter polymeric materials. A two-dimensional spatial resolution of better than 15 nm was achieved. With better detectors and brighter and more coherent X-ray beams, radiation-sensitive PFSA ionomers will be visualized with acceptable levels of chemical and structural modification. This work is a step toward visualization of ionomers in PEMFC cathodes at high spatial resolution (presently sub-15 nm, but ultimately below 10 nm), which will be transformative with respect to optimization of PEMFCs for automotive use

Additional file 5: Figure S5. of Mesenchymal stem cell-derived angiogenin promotes primodial follicle survival and angiogenesis in transplanted human ovarian tissue

Representative images showing triple staining of Ki67, DAPI and CD31 in ovarian graft with or without co-transplantation of MSCs. Vasculature is shown in red, cell nuclei are shown in blue and Ki67 positive nuclei are shown in green. Scale bar = 50 μm. (JPG 299 kb

Oxygen-Controlled Hydrogen Evolution Reaction: Molecular Oxygen Promotes Hydrogen Production from Formaldehyde Solution Using Ag/MgO Nanocatalyst

Molecular hydrogen is one of the essential reactants in the chemical industry, and its generation from renewable sources such as biomass materials and water is of great benefit to the future society. Generally, molecular oxygen should be pre-eliminated in the hydrogen evolution reactions (HERs) in order to avoid the reverse hydrogen oxidation reaction (HOR). Here, we report a highly efficient HER from a formaldehyde/water mixture using MgO supported Ag nanoparticles (AgNPs/MgO) as the catalyst and molecular oxygen as a promoter. The HER rate depends almost linearly on the oxygen partial pressure, and the optimal turnover frequency (TOF) of the silver catalyst exceeds 6,600 h^–1. Based on the experimental and theoretical results, a surface stabilized MgO/Ag–^•OOH complex is suggested to be the main catalytically active species for the HER