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Real-time in situ X-ray analysis was used to shed light on the topotactic transformation of NH4TiOF3 into nanostructured TiO2 mesocrystals. Specifically, for the system formed in the ...presence of the PEG-2000 templating polymer, XRD analysis showed that the overall transformation occurs through four separate transitions, consistent with previous reports. The applicability of synchrotron wide-angle X-ray scattering (WAXS) to real-time in situ analysis has enabled precise temperature mapping of these four transitions and the identification of stability boundaries for the first time.
Epitaxial VO2 films on r-sapphire substrates with ideal composition, dense structure and superior functional properties were obtained by water-assisted MOCVD from vanadyl hexafluoroacetylacetonate ...followed by the annealing under optimized conditions. The obtained films exhibit both intense optical switch properties in IR region and unique MIT characteristics: change in resistance by 4.6 orders in the temperature range 40–80 °C, hysteresis width less 0.7 °C and transition width 1.5 °C. The proposed synthetic approach opens new opportunities to fabricate highly sensitive and ultrafast switches for optical, electronic and biomedical devices.
•Highly oriented (100)VO2 films grown on r-Al2O3 at 350 °C using MOCVD based on reaction between VO(hfa)2 and water vapors.•Manipulation with MIT of VO2 by annealing under controlling oxygen pressure in ranges of 15–120 min and 550–650 °C.•Record MIT parameters for VO2 films: change in resistance by 4.6 hysteresis width less 0.7 °C and transition width 1.5 °C.•Ultra-sharp electrical and optical MIT (IR reflectance) for epitaxial VO2 films.•The new model of VO2 recrystallization at temperatures below 600 °C based on melting of VxO2x+1 impurities.
Vanadium dioxide (VO2) nanocrystalline materials are of great interest as for modern electronics and photonics as well as for energy saving technologies. Nevertheless, there still remains a challenge ...to realize their controllable synthesis, as evidenced by the low rate of implantation of existing technologies into mass production. Here, a hydrothermal reaction in a water-ethylene glycol (EG) solution has been coupled with the post-deposition annealing, yielding a range of phase-pure vanadium dioxide nanostructures on single-crystal r-sapphire substrate. A directed change in the viscosity of the precursor solution by using a change in the EG : H2O ratio makes it possible to control the nucleation rate and thus form VO2 isolated nanocrystals, as well as their ordered ensembles with regular distribution and uniform films on the substrate. The obtained nanostructures were extensively characterized by Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. Continuous VO2 nanostructures demonstrated a metal-insulator transition (MIT) with a jump in resistivity of about 103–104, as well as a giant terahertz (THz) modulation depth up to 86 % (in the range from 0.3 to 2.0 THz), which confirms their high-quality and the possibility of their use in the creation of functional electronic and THz optical devices.
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•A new hybrid MCs TiO2-K2Ti6O13 material was successfully synthesized.•The obtained hybrid material exhibited 50% higher activity than the commercial Evonik Aeroxide® TiO2 P25 ...photocatalyst.•The low-temperature solid-state approach of potassium hexatitanate was suggested.
Here we describe the development of a new mesocrytalline anatase-based photocatalyst with an activity nearly double that of the commercial Evonik Aeroxide® TiO2 P25 catalyst. An extensive characterization of this new catalytic material with XRD, TEM, SAED, EELS, SEM, RAMAN and XPS shows that its activity is promoted by its hybrid structure comprising mesocrystalline anatase and K2Ti6O13 whiskers formed within the TiO2 mesocrystals. This new and unexpected component is formed in situ within the TiO2 mesocrystalline framework at a surprisingly low temperature of 500 °C as a result of potassium diffusion from polymer-matrix phase. The growth of whiskers occurs at the 001 TiO2 planes of mesocrystals and their sizes attain 60 nm in a section and a few μm in length.
One of the possible ways to enhance photocatalytic activity is the use of photonic band gap (PBG) materials. Anodic titania photonic crystals (PhCs) are promising PBG structures, whose structure can ...be tuned easily by anodizing conditions. However, the effect of various doping approaches on the photocatalytic activity of anodic titania PhCs has never been studied before. Here anodic titania PhCs were synthesized by cycling anodizing of titanium with voltage versus charge density modulation followed by annealing at 450 °C in air. The PhCs were post-treated by electrochemical reduction in 0.1 M Na2SO4, annealing in H2/Ar mixture or NH3. The phase composition and structure of titania PhCs were studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. Photocatalytic activity of PhCs in the degradation of the methylene blue dye decreases after electrochemical reduction and annealing in NH3, whereas the annealing in H2/Ar at 600 °C for 2 h leads to an increase in the degradation rate constant by 60%.
•Cyclic anodizing is applied for the preparation of 1D titania photonic crystals (PhCs).•Amount of oxygen vacancies in TiO2 increases after annealing in H2/Ar and NH3.•Photocatalytic activity of PhCs is demonstrated for methylene blue (MB) degradation.•Photocatalytic activity of PhCs decreases after electroreduction or annealing in NH3.•Annealing in H2/Ar leads to a 60% increase in the rate constant of MB degradation.
The present study reports the fast synthesis of VO2 (М1) oriented films on the r-Al2O3(012) substrates by the hydrothermal method using citric acid and vanadium (V) oxide as precursors with post ...deposition annealing in inert atmosphere. The effects of synthesis parameters (solution concentration and autoclave filling factor) on the films composition, morphology and electric properties are considered using XRD, Raman spectroscopy, AFM and SEM. The obtaining VO2(M1)/r-Al2O3 films show a metal-insulator transition with resistivity change of ~3.5 orders of magnitude and excellent thermochromic properties in the long-wavelength IR region. This work demonstrates a promising technique to promote the commercial implementation of VO2 as material for design of infrared (IR) switch devices.
An array of highly oriented anatase nanoparticles was successfully prepared from NH
TiOF
with the assistance of polyetheleneglycol-400 at 450 °C. The study showed the stability of obtained layered ...TiO
-anatase close to 1200 °C. This research confirmed for the first time that the transition of mesocrystalline anatase to the rutile phase occurs between 1000 °C and 1200 °C, which is more than 400 °C higher than the transition of bulk TiO
due to the used precursor. A small quantity of K-phase nanowhiskers, which issued after 800 °C in the composite based on TiO
, stimulated a fourfold increase in photocatalytic performance. This study offers a new approach to the construction and preparation of effective nanocrystalline photocatalyst.
Evidence-based therapies used to treat coronavirus disease (COVID-19) remain limited. Azoximer bromide (AZB; Polyoxidonium
) is an immunomodulating molecule frequently used in the Russian Federation. ...It offers demonstrable therapeutic benefit in upper respiratory tract infections. This study evaluated the safety and efficacy of AZB when used in combination with standard of care treatment in patients hospitalized with COVID-19.
Hospitalized patients with COVID-19 (
=81; nine sites) received AZB 12 mg intravenously once daily for 3 days then intramuscularly every other day until day 17. The primary endpoint included clinical status at day 15
baseline. Historical control data of 100 patients from a randomized, controlled, open-label trial conducted in China were included to serve as a direct control group.
Notable clinical improvement, assessed by seven-point ordinal scale (OS) score and National Early Warning Score, was observed. Mean duration of hospitalization was 19.3 days. Indicators of pneumonia and lung function showed gradual recovery to normalization. No patients died but, by day 28, one patient still required respiratory support; this patient died on day 34. A higher proportion of patients receiving AZB required invasive or non-invasive ventilation (OS 5 or 6) at baseline compared with the historical control group. Improvement in mean OS score by day 14/15 was not notable in the control group (OS 3.99-3.87) but was clear in the AZB group (OS 4.36-2.90). Mean duration of hospitalization was similar in the control group (16.0 days); however, day 28 mortality was higher, at 25.0% (
=25).
AZB combined with standard of care was safe and well tolerated. An apparent clinical improvement could not be fully evaluated due to the lack of a direct control group; further assessment of AZB for the treatment of COVID-19 in a randomized, placebo-controlled study is warranted.
Ceramics based on rhenanite CaNaPO4 with density of 0.94 g/cm3 and compressive strength of 10.3 MPa was obtained via firing at 900 °C of composite cement-salt stone prepared from a hardening powder ...mixture of calcium citrate tetrahydrate Ca3(C6H5O7)2∙4H2O and sodium dihydrogen phosphate NaH2PO4. The phase composition of the obtained samples of cement–salt stone was represented by monetite CaHPO4, unreacted sodium dihydrogen phosphate and calcium citrate tetrahydrate. According to the XRD data, the phase composition of the ceramic samples after annealing in the temperature range of 500–700 °C was mainly represented by the β-CaNaPO4 phase. It was found that after an annealing at temperature of 900 °C, the phase composition of ceramics was presented with the only phase of β-CaNaPO4. It was demonstrated that an increase in the annealing temperature led to an increase in the grain size from 1 μm after annealing at 500 °C to 5 μm after annealing at 900 °C. Obtained ceramic material based on CaNaPO4 could be important for regenerative treatments of bone tissue defects.
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