245 research outputs found
Ionic Liquids as Designer Solvents for the Synthesis of Metal Nanoparticles
Size and shape-controlled synthesis of metal nanostructures has received significant interest in materials research, as metal nanoparticles are likely to have a considerable impact upon the fields of catalysis, sensing, photonics, optoelectronics and biology, due to their unique size- and shape-tunable physico-chemical properties (Hao et al., 2004; Burda et al., 2005; Shukla et al., 2005; Lu et al., 2009; Sardar et al., 2009). With significant developments in this field, the current focus is predominantly on synthesis of ultra-fine (sub-10 nm) metal nanoparticles with narrow size distribution that remain stable in reaction media, tuning the shape of metal nanostructures, to understand the metal nanoparticles shape-guiding mechanisms, and to understand their structure-property correlation (Lu et al., 2009). To prepare metal nanoparticles (colloids), the most commonly employed approach is the bottom-up wet-chemistry approach. In this approach, typically in the presence of a capping/stabilizing agent, metal ions are controllably reduced, wherein individual metal atoms combine to form metal nanoparticles stabilized by capping agents. Although in few instances reducing agents themselves act as stabilizers, capping agents are generally considered essential to minimize the surface free energy of metal nanoparticles, which would otherwise aggregate in the absence of these capping agents. In most of the well established wet-chemistry routes of metal nanoparticles synthesis, aqueous or organic solvents are generally employed, while the use of ionic liquids (ILs) for synthesis of metal nanoparticles is a relatively recent phenomenon
Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide
Materials that undergo reversible metal-insulator transitions are obvious
candidates for new generations of devices. For such potential to be realised,
the underlying microscopic mechanisms of such transitions must be fully
determined. In this work we probe the correlation between the energy landscape
and electronic structure of the metal-insulator transition of vanadium dioxide
and the atomic motions occurring using first principles calculations and high
resolution X-ray diffraction. Calculations find an energy barrier between the
high and low temperature phases corresponding to contraction followed by
expansion of the distances between vanadium atoms on neighbouring sub-lattices.
X-ray diffraction reveals anisotropic strain broadening in the low temperature
structure's crystal planes, however only for those with spacings affected by
this compression/expansion. GW calculations reveal that traversing this barrier
destabilises the bonding/anti-bonding splitting of the low temperature phase.
This precise atomic description of the origin of the energy barrier separating
the two structures will facilitate more precise control over the transition
characteristics for new applications and devices.Comment: 11 Pages, 8 Figure
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Conversion of γ-Valerolactone to Ethyl Valerate over Metal Promoted Ni/ZSM-5 Catalysts : Influence of Ni0/Ni2+ Heterojunctions on Activity and Product Selectivity
Promoter (Cr, Mo and W) modified Ni/ZSM-5 catalysts were explored in the vapor phase conversion of γ-valerolactone (GVL) to ethyl valerate (EV; gasoline blender) at atmospheric pressure. Among the three different promoters (Cr, Mo and W) tested the Mo-modified catalyst was found to be the best candidate. In addition, this catalyst was found to be stable up to 50 h reaction time with an insignificant decrease in activity. The good catalytic performance is related to an optimal ratio of acid and hydrogenation functions provided by Ni2+ and Ni0, respectively. In situ FTIR spectroscopic studies revealed a strong adsorption of GVL on all catalysts which quickly reacts with dosed ethanol by formation of EV, most pronounced on the Mo-modified catalyst, while VA was identified as side product. These findings suggest the preferred GVL ring opening by cracking the C−O bond on the methyl side of the GVL molecule on this type of catalysts leading to pentenoic acid as intermediate, which is quickly hydrogenated and esterified. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Absence of Morphotropic Phase Boundary Effects in BiFeO3-PbTiO3 Thin Films Grown via a Chemical Multilayer Deposition Method
Here, we report the unusual behaviour shown by the (BiFeO3)1-x-(PbTiO3)x
(BF-xPT) films prepared using a multilayer deposition approach by chemical
solution deposition method. Thin film samples of various compositions were
prepared by depositing several bilayers of BF and PT precursors by varying the
BF or PT layer thicknesses. X-ray diffraction showed that final samples of all
compositions show mixing of the two compounds resulting in a single phase
mixture, also confirmed by transmission electron microscopy. In contrast to
bulk equilibrium compositions, our samples show a monoclinic (MA type)
structure suggesting disappearance of morphotropic phase boundary (MPB) about x
= 0.30 as observed in the bulk. This is accompanied by the lack of any
enhancement of remnant polarization at MPB as shown by the ferroelectric
measurements. Magnetic measurements show that the magnetization of the samples
increases with increasing BF content. Significant magnetization of the samples
indicates melting of spin spirals in the BF-xPT arising from random
distribution of iron atoms across the film. Absence of Fe2+ ions in the films
was corroborated by X-ray photoelectron spectroscopy measurements. The results
illustrate that used thin film processing methodology significantly changes the
structural evolution in contrast to predictions from the equilibrium phase
diagram as well as modify the functional characteristics of BP-xPT system
dramatically.Comment: 15 pages, 6 figure
Cationic Amino Acids Specific Biomimetic Silicification in Ionic Liquid: A Quest to Understand the Formation of 3-D Structures in Diatoms
The intricate, hierarchical, highly reproducible, and exquisite biosilica structures formed by diatoms have generated great interest to understand biosilicification processes in nature. This curiosity is driven by the quest of researchers to understand nature's complexity, which might enable reproducing these elegant natural diatomaceous structures in our laboratories via biomimetics, which is currently beyond the capabilities of material scientists. To this end, significant understanding of the biomolecules involved in biosilicification has been gained, wherein cationic peptides and proteins are found to play a key role in the formation of these exquisite structures. Although biochemical factors responsible for silica formation in diatoms have been studied for decades, the challenge to mimic biosilica structures similar to those synthesized by diatoms in their natural habitats has not hitherto been successful. This has led to an increasingly interesting debate that physico-chemical environment surrounding diatoms might play an additional critical role towards the control of diatom morphologies. The current study demonstrates this proof of concept by using cationic amino acids as catalyst/template/scaffold towards attaining diatom-like silica morphologies under biomimetic conditions in ionic liquids
Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance
Silicon-based contaminants are ubiquitous in natural graphite, and they are thus expected to be present in exfoliated graphene. Here, the authors show that such impurities play a non-negligible role in graphene-based devices, and use high-purity parent graphite to boost the performance of graphene sensors and supercapacitor microelectrodes
Remdesivir and three other drugs for hospitalised patients with COVID-19: final results of the WHO Solidarity randomised trial and updated meta-analyses.
BACKGROUND
World Health Organization expert groups recommended mortality trials of four repurposed antiviral drugs - remdesivir, hydroxychloroquine, lopinavir, and interferon beta-1a - in patients hospitalized with coronavirus disease 2019 (Covid-19).
METHODS
We randomly assigned inpatients with Covid-19 equally between one of the trial drug regimens that was locally available and open control (up to five options, four active and the local standard of care). The intention-to-treat primary analyses examined in-hospital mortality in the four pairwise comparisons of each trial drug and its control (drug available but patient assigned to the same care without that drug). Rate ratios for death were calculated with stratification according to age and status regarding mechanical ventilation at trial entry.
RESULTS
At 405 hospitals in 30 countries, 11,330 adults underwent randomization; 2750 were assigned to receive remdesivir, 954 to hydroxychloroquine, 1411 to lopinavir (without interferon), 2063 to interferon (including 651 to interferon plus lopinavir), and 4088 to no trial drug. Adherence was 94 to 96% midway through treatment, with 2 to 6% crossover. In total, 1253 deaths were reported (median day of death, day 8; interquartile range, 4 to 14). The Kaplan-Meier 28-day mortality was 11.8% (39.0% if the patient was already receiving ventilation at randomization and 9.5% otherwise). Death occurred in 301 of 2743 patients receiving remdesivir and in 303 of 2708 receiving its control (rate ratio, 0.95; 95% confidence interval [CI], 0.81 to 1.11; P = 0.50), in 104 of 947 patients receiving hydroxychloroquine and in 84 of 906 receiving its control (rate ratio, 1.19; 95% CI, 0.89 to 1.59; P = 0.23), in 148 of 1399 patients receiving lopinavir and in 146 of 1372 receiving its control (rate ratio, 1.00; 95% CI, 0.79 to 1.25; P = 0.97), and in 243 of 2050 patients receiving interferon and in 216 of 2050 receiving its control (rate ratio, 1.16; 95% CI, 0.96 to 1.39; P = 0.11). No drug definitely reduced mortality, overall or in any subgroup, or reduced initiation of ventilation or hospitalization duration.
CONCLUSIONS
These remdesivir, hydroxychloroquine, lopinavir, and interferon regimens had little or no effect on hospitalized patients with Covid-19, as indicated by overall mortality, initiation of ventilation, and duration of hospital stay. (Funded by the World Health Organization; ISRCTN Registry number, ISRCTN83971151; ClinicalTrials.gov number, NCT04315948.)
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