M. Josefina Arellano-Jiménez

Atomic cobalt on nitrogen-doped graphene for hydrogen generation

Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.

High-Performance Hydrogen Evolution from MoS2(1-x) P(x) Solid Solution.

A MoS2(1-x) P(x) solid solution (x = 0 to 1) is formed by thermally annealing mixtures of MoS2 and red phosphorus. The effective and stable electrocatalyst for hydrogen evolution in acidic solution holds promise for replacing scarce and expensive platinum that is used in present catalyst systems. The high performance originates from the increased surface area and roughness of the solid solution.

High-resolution analytical imaging and electron holography of magnetite particles in amyloid cores of Alzheimer’s disease

Abnormal accumulation of brain metals is a key feature of Alzheimer’s disease (AD). Formation of amyloid-β plaque cores (APC) is related to interactions with biometals, especially Fe, Cu and Zn, but their particular structural associations and roles remain unclear. Using an integrative set of advanced transmission electron microscopy (TEM) techniques, including spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM), nano-beam electron diffraction, electron holography and analytical spectroscopy techniques (EDX and EELS), we demonstrate that Fe in APC is present as iron oxide (Fe3O4) magnetite nanoparticles. Here we show that Fe was accumulated primarily as nanostructured particles within APC, whereas Cu and Zn were distributed through the amyloid fibers. Remarkably, these highly organized crystalline magnetite nanostructures directly bound into fibrillar Aβ showed characteristic superparamagnetic responses with saturated magnetization with circular contours, as observed for the first time by off-axis electron holography of nanometer scale particles.

Ultrastructural changes in methicillin-resistant Staphylococcus aureus induced by positively charged silver nanoparticles

Summary Silver nanoparticles offer a possible means of fighting antibacterial resistance. Most of their antibacterial properties are attributed to their silver ions. In the present work, we study the actions of positively charged silver nanoparticles against both methicillin-sensitive Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. We use aberration-corrected transmission electron microscopy to examine the bactericidal effects of silver nanoparticles and the ultrastructural changes in bacteria that are induced by silver nanoparticles. The study revealed that our 1 nm average size silver nanoparticles induced thinning and permeabilization of the cell wall, destabilization of the peptidoglycan layer, and subsequent leakage of intracellular content, causing bacterial cell lysis. We hypothesize that positively charged silver nanoparticles bind to the negatively charged polyanionic backbones of teichoic acids and the related cell wall glycopolymers of bacteria as a first target, consequently stressing the structure and permeability of the cell wall. This hypothesis provides a major mechanism to explain the antibacterial effects of silver nanoparticles on Staphylococcus aureus. Future research should focus on defining the related molecular mechanisms and their importance to the antimicrobial activity of silver nanoparticles.

Metallic Two-Dimensional Nanoframes: Unsupported Hierarchical Nickel–Platinum Alloy Nanoarchitectures with Enhanced Electrochemical Oxygen Reduction Activity and Stability

Electrochemical oxygen reduction reaction (ORR) catalysts that have both high activities and long-term stabilities are needed for proton-exchange membrane fuel cells (PEMFCs) and metal-air batteries. Two-dimensional (2D) materials based on graphene have shown high catalytic activities, however, carbon-based materials result in significant catalyst degradation due to carbon oxidation that occurs at high electrochemical potentials. Here, we introduce the synthesis and electrochemical performance of metallic 2D nanoframes which represent a new approach to translate 2D materials into unsupported (carbon-free) electrocatalysts that have both significantly higher ORR catalytic activities and stabilities compared with conventional Pt/carbon electrocatalysts. Metallic Ni-Pt 2D nanoframes were synthesized by controlled thermal treatments of Pt-decorated Ni(OH)2 nanosheets. The nanoframes consist of a hierarchical 2D framework composed of a highly catalytically active Pt-Ni alloy phase with an interconnected solid and pore network that results in three-dimensional molecular accessibility. The inclusion of Ni within the Pt structure resulted in significantly smaller Pt lattice distances compared to those of Pt nanoparticles. On the basis of its unique local and extended structure, the ORR specific activity of Ni-Pt 2D nanoframes (5.8 mA cmPt-2) was an order of magnitude higher than Pt/carbon. In addition, accelerated stability testing at elevated potentials up to 1.3 VRHE showed that the metallic Ni-Pt nanoframes exhibit significantly improved stability compared with Pt/carbon catalysts. The nanoarchitecture and local structure of metallic 2D nanoframes results in high combined specific activity and elevated potential stability. Analysis of the ORR electrochemical reaction kinetics on the Ni-Pt nanoframes supports that at low overpotentials the first electron transfer is the rate-determining step, and the reaction proceeds via a four electron reduction process. The ability to create metallic 2D structures with 3D molecular accessibility opens up new opportunities for the design of high activity and stability carbon-free catalyst nanoarchitectures for numerous electrocatalytic and catalytic applications.

Diffusion and recrystallization of B implanted in crystalline and pre-amorphized Ge in the presence of F

Although the diffusion control and dopant activation of Ge p-type junctions are straightforward when using B+ implantation, the use of the heavier BF2+ ions or even BF+ is still favored in terms of shallow junction formation and throughput—because implants can be done at higher energies, which can give higher beam currents and beam stability—and thus the understanding of the effect of F co-doping becomes important. In this work, we have investigated diffusion and end-of-range (EOR) defect formation for B+, BF+, and BF2+ implants in crystalline and pre-amorphized Ge, employing rapid thermal annealing at 600 °C and 800 °C for 10 s. It is demonstrated that the diffusion of B is strongly influenced by the temperature, the presence of F, and the depth of amorphous/crystalline interface. The B and F diffusion profiles suggest the formation of B–F complexes and enhanced diffusion by interaction with point defects. In addition, the strong chemical effect of F is found only for B in Ge, while such an effect is van...

Zinc oxide decorated multi-walled carbon nanotubes: their bolometric properties

We report the synthesis of MWNTs/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNT with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs is covered with ZnO nanoparticles, such particles form highly porous spherical nodules of 50-150 nm in diameter, sizes that are in values one order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, in the self-assembled nanocomposite the ZnO exhibits a large surface to volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNTs/ZnO nanocomposites were characterized by X-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-Vis and Raman spectroscopies. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K, and up to -18%/K, on temperature change intervals from 10 K to 1 K, respectively. Based on TCR results, the nanocomposite MWNTs/ZnO prepared in this work is a promising material with potential application as a bolometric sensor.We report the synthesis of MWNT/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNTs with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs was covered with ZnO nanoparticles; these particles formed highly porous spherical nodules of 50-150 nm in diameter, sizes that are an order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, the self-assembled nanocomposite the ZnO exhibited a large surface-to-volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNT/ZnO nanocomposites were characterized by x-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-vis and Raman spectroscopy. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K up to -18%/K, over temperature change intervals from 10 K to 1 K. Based on these TCR results, the nanocomposite MWNT/ZnO prepared in this work is a promising material, with potential application as a bolometric sensor.

A novel one-pot room-temperature synthesis route to produce very small photoluminescent silicon nanocrystals

AbstractA novel strategy to synthesize photoluminescent silicon nanocrystals (SiNCs) from a reaction between tetraethylorthosilicate (TEOS) and trimethyl-hexadecyl-ammonium borohydride (CTABH4) in organic solvent is presented. The formation reaction occurs spontaneously at room temperature in homogeneous phase. The produced silicon nanocrystals are characterized by using their photoluminescent properties and via HRTEM. In addition, theoretical calculations of the optical absorption spectrum of silicon quantum dots in vacuum with different sizes and surface moieties were performed in order to compare with the experimental findings. The new chemical reaction is simple and can be implemented to produce silicon nanocrystal with regular laboratory materials by performing easy and safe procedures. Graphical abstractᅟ

Integrative structural and advanced imaging characterization of manganese oxide nanotubes doped with cobaltite

Manganese oxide nanotubes (MnO2) were efficiently produced through a hydrothermal method, using SiO2 powder as nucleation points, then doped with cobaltite (Co3O4) nanoparticles uniformly deposited along the surface of the MnO2 nanotubes. An integrative approach using advanced analytical electron microscopy techniques (UHR FE-SEM, HR-TEM, and BF/HAADF-STEM, coupled with EDX) in combination with spectroscopy allowed the determination of the structural characteristics of this composite nanomaterial. Advanced imaging clearly revealed the tubular structure of the MnO2 nanotubes (diameter of 30–80 nm and length of 3–5 μm) and the arrangement of the discrete Co3O4 deposits (10–40 nm). Remarkably, high-resolution and spherical aberration-corrected STEM imaging allowed for the determination of the crystalline arrangement of the nanomaterials, particularly at the interface between MnO2 and Co3O4 particles with high spatial sub-Angstrom resolution, revealing the distribution and high structural consistency of the novel composite materials produced. Furthermore, X-ray diffraction and Raman spectroscopy confirmed that MnO2 corresponded to the crystallographic phase cryptomelane (K2-xMn8O16), while the dopant cobalt nanoparticles adopted a cobaltite (Co3O4) phase. We demonstrated the catalytic properties of the composite MnO2–Co3O4 nanotubes as an electrocatalyst material for oxygen evolution, where it showed superior behaviour, with a significantly higher catalytic activity (6.8 times) than pure MnO2 in the OER region.

Copper complexes within the supramolecular solid structure of cyanuric acid and melamine

ABSTRACT A complex of copper sulfate was formed by impregnation of the cyanuric acid melamine adduct (CAM) with a solution of copper (II) sulfate. A thermal treatment at 250°C of the dried compound delivered a greenish powder. The UV-Vis spectroscopy showed that an absorption around 700 nm is compatible with a copper (II) sulfate complex coordinated inside the supramolecular structure of CAM. No copper or copper oxide particles were found by means of either transmission or scanning electron microscopy. X-ray photoelectron spectroscopy showed that on the surface there was a considerable amount of Cu(I) (66%) probably coordinated also inside the CAM channels. A brief catalytic test showed the ability of the copper complexes to oxidize sucrose to gluconic acid.