Masks for COVID-19.

Sustainable solutions on fabricating and using a face mask to block the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread during this coronavirus pandemic of 2019 (COVID-19) are required as society is directed by the World Health Organization (WHO) toward wearing it, resulting in an increasingly huge demand with over 4 000 000 000 masks used per day globally. Herein, various new mask technologies and advanced materials are reviewed to deal with critical shortages, cross-infection, and secondary transmission risk of masks. A number of countries have used cloth masks and 3D-printed masks as substitutes, whose filtration efficiencies can be improved by using nanofibers or mixing other polymers into them. Since 2020, researchers continue to improve the performance of masks by adding various functionalities, for example using metal nanoparticles and herbal extracts to inactivate pathogens, using graphene to make masks photothermal and superhydrophobic, and using triboelectric nanogenerator (TENG) to prolong mask lifetime. The recent advances in material technology have led to the development of antimicrobial coatings, which are introduced in this review. When incorporated into masks, these advanced materials and technologies can aid in the prevention of secondary transmission of the virus

A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance

TiO2 hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO2 nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO2 and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers.Published versio

Boosting the oxygen evolution activity in non-stoichiometric praseodymium ferrite-based perovskites by A site substitution for alkaline electrolyser anodes

Sustainable fossil fuel free systems are crucial for tackling climate change in the global energy market, and the identification and understanding of catalysts needed to build these systems plays a vital role in their development. ABO3−δ perovskite oxides have been observed to be potential replacement materials for the high-performing, but low ionic conducting and economically unfavourable Pt and IrO2 water splitting catalysts. In this work increased addition of Sr2+ aliovalent dopant ions into the crystal lattice of Pr1−xSrxFeO3−δ perovskites via A site substitution was seen to drastically improve the electrocatalytic activity of the oxygen evolution reaction (OER) in alkaline environments. The undoped PrFeO3−δ catalyst was not catalytically active up to 1.70 V against the reversible hydrogen electrode (RHE), whilst an onset potential of 1.62 V was observed for x = 0.5. Increased strontium content in Pr1−xSrxFeO3−δ was found to cause a reduction in the lattice parameters and crystal volume whilst retaining the orthorhombic Pbnm space group throughout all dopant levels, analysed using the Rietveld method. However, it was noted that the orthorhombic distortion was reduced as more Sr2+ replaced Pr3+. The mechanism for the increased electrocatalytic activity with increased strontium is due to the increasing concentration of oxygen vacancy (δ), leading to increased catalyst site availability, and the increased average oxidation state of Fe cations, consistent with the iodometric titration results. This results in shifting the average d shell eg electron filling further towards unity. X-ray photoelectron spectrum of the O 1s core level also shows the presence of lattice oxide and surface hydroxide/carbonate. This work shows promise in that using the more abundant and more economically friendly material of strontium allows for improved OER catalytic activity in otherwise inactive perovskite catalyst oxides

Morphology, structure and electrochemical properties of single phase electrospun vanadium pentoxide nanofibers for lithium ion batteries

One-dimensional (1D) vanadium pentoxide (V2O5) nanofibers (VNF) are synthesized by electrospinning vanadium sol–gel precursors containing vanadyl acetylacetonate and poly(vinylpyrrolidone) followed by sintering. Crystal structure, molecular structure and morphology of electrospun VNF are analyzed using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area diffraction (SAED), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Single-phase electrospun VNF not, vert, similar300–800 nm in diameter, 20–50 μm long (aspect ratio > 50) with porous interconnected fibrous morphology are revealed by FESEM and TEM analysis. Electrochemical properties of the sintered VNF, as a cathode in lithium-ion batteries, explored using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) give rise to new understandings of the electrochemical processes occurring in these nanofibrous cathodes. Electrospun VNF exhibits initial discharge capacity not, vert, similar316 mAh g−1 (not, vert, similar2.2 Li per V2O5) in the voltage range of 1.75 and 4.0 V vs. Li/Li+ at 0.1 C rate. When cycled at a reduced voltage range of 2.0–4.0 V vs. Li/Li+, less phase transitions occur, giving rise to the initial specific capacity of 308 mAh g−1 and improved cyclic retention of 74% after 50 cycles.Accepted versio

Microwave Synthesis of Noncentrosymmetric BaTiO 3 Truncated Nanocubes for Charge Storage Applications

Truncated nanocubes of barium titanate (BT) were synthesized using a rapid, facile microwave-assisted hydrothermal route. Stoichiometric composition of pellets of nanocube BT powders was prepared by two-stage microwave process. Characterization by powde

Crystal chemistry and optimization of conductivity in 2A, 2M and 2H alkaline earth lanthanum germanate oxyapatite electrolyte polymorphs

Calcium (La10-xCaxGe6O27-x/2, 0 ≤ x ≤ 2.57) and barium (La10-xBaxGe6O27-x/2, 0 ≤ nominal x ≤ 3) doped lanthanum germanate apatites were synthesized by high temperature solid-state sintering. The lattice parameters obtained from Rietveld refinemen

Sensory modulation of hippocampal transmission. II. Evidence for a cholinergic locus of inhibition in the Schaffer-CA1 synapse

11 páginas, 7 figuras.The present work studied the neurotransmitter mediating the depressive effect of sensory stimulation on the Schaffer-CA1 transmission. Field responses of the CA1 region evoked by ipsilateral CA3 stimuli were recorded in paralyzed, locally anesthetized rats following the same experimental paradigm as in the previous work. The tissue zone under recording was perfused in vivo by an implanted hollow fiber (brain dialysis device) with either Krebs-Ringer bicarbonate (KRB), or KRB with penicillin, atropine, acetylcholine or eserine. Results were the following: (1) atropine-increased the field excitatory postsynaptic potential (EPSP) amplitude in a dose-dependent manner and totally abolished the modulatory action of sensory stimulation; (2) both the field EPSP and the modulatory action of sensory stimulation remained unaltered during the blockade of GABAergic activity by penicillin; (3) acetylcholine as well as eserine induced a great diminution of both field EPSP and population spike amplitudes, without altering the effect of sensory stimulation; (4) penicillin and atropine induced multiple population spikes, reversing the effect of sensory stimulation and increasing the cell excitability. These results demonstrate that the sensory modulation of information transfer through the Schaffer-CA1 synapse is mediated by a muscarinic cholinergic mechanism. The dose-dependent increase in the field EPSP by muscarinic blockade is evidence for the existence of a cholinergic presynaptic inhibition on the Schaffer collateral terminals.O.H. is the recipient of a fellowship from the Spanish F.I.S.S. (85/632).Peer reviewe

New mechanisms of void growth in Au-Al wire bonds: Volumetric shrinkage and intermetallic oxidation

This letter examines void nucleation and coalescence in Au-Al wire bonds using high-resolution transmission electron microscopy. It is found that void formation is not only attributed to Kirkendall-type migration as conventionally believed, but also due to volumetric shrinkage and intermetallic oxidation. A volumetric shrinkage of a few percent is associated with intermetallic growth and phase transformations. Intermetallic oxidation occurs at the intermetallics/alumina interface and the migration of oxygen towards the intermetallics leads to void growth and thickening of the surrounding oxide walls