Towards understanding photon absorption and emission in MgAl layered double hydroxide

SUPPLEMENTARY INFORMATION : The Rietveld refinement, the bandgap determination, the deconvolution of the MIR spectrum, more information on the MgAl-LDH luminescence reproducibility, the comparison of luminescence intensity with excitation at 5.0 eV and 3.8 eV, the linear combination of luminescence spectra, a thorough description of deconvoluted excitable states, the X-ray photoelectron analysis of MgAl-LDH (O 1s), additional data on the calcined MgAl-LDH (luminescence at 298 K and MIR spectra), and the full spectrum luminescence of MgAl-LDH to 1000 nm.Please read abstract in the article.https://pubs.rsc.org/en/journals/journal/mahj2023Chemical EngineeringChemistr

Comparison of nano-structured transition metal modified tri-metal MgMAl-LDHs (M = Fe, Zn, Cu, Ni, Co) prepared using co-precipitation

Comparison of layered double hydroxides (LDHs) synthesised using different methods, conditions and post-treatment is difficult to achieve because these greatly modify their material properties. This paper aims to provide a comparison of material properties for modified quintinite, where all LDHs were synthesised at the same conditions – thus allowing for direct comparison of the material properties obtained. Nano-structured materials were formed in all cases. The nano-structured transition metal (TM) MgMAl–LDHs were synthesised using constant pH co-precipitation. Five TMs (M = Fe, Co, Ni, Cu, Zn) were included in the LDH layers with molar substitutions of 0.5%, 1%, 5%, 10%, and 25% based on Mg-replacement for divalent TM cations and Al-replacement for trivalent TM cations. The materials were characterised using powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared analysis (ATR-FTIR), thermogravimetric analysis (TGA) and particle size analysis (PSA). The modified LDHs were synthesised free of major by-products and with similar morphologies. It could be shown that the crystallite dimensions varied between the different TM substitutions, that morphological changes were visible for some of the TMs used, that the processability depended on the TMs substituted, and that the substitution of TMs influenced the thermal stability of the LDHs.Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (Department of Trade and Industry, South Africa).http://pubs.rsc.org/en/journals/journalissues/rahj2020Chemical Engineerin

Comparison of transition metal (Fe, Co, Ni, Cu, and Zn) containing tri-metal layered double hydroxides (LDHs) prepared by urea hydrolysis

This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis. Transition-metal-substituted MgMAl-LDHs were synthesized with M = Fe, Co, Ni, Cu or Zn. 5 mol% and 10 mol% substitutions were performed, where Mg was substituted with Co, Ni, Cu and Zn, and Al with Fe. The successful synthesis of crystalline MgMAl-LDHs was confirmed using X-ray powder diffraction (XRD) analysis. Energy-dispersive X-ray (EDX) spectroscopy was used to identify substituted metals and determine changes in composition. Changes in morphology were studied using scanning electron microscopy (SEM). Thermogravimetric analysis was used to determine the effect of Fe-, Co-, Ni-, Cu- or Zn-substitution on the thermal degradation of the MgMAl-LDH phase. The structure, morphology and thermal behavior of the LDHs were shown to be influenced by the substituted transition metals. The observed thermal stability took the order MgNiAl- > MgFeAl- = MgAl- ≥ MgCoAl- > MgCuAl- > MgZnAl-LDH. The urea hydrolysis method was shown to be a simple preparation method for well-defined crystallite structures with large hexagonal platelets and good distribution of transition metal atoms in the substituted LDHs.Pakistan and German Academic Exchange Service (Higher Education Commission) and Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (Department of Trade and Industry, South Africa).http://pubs.rsc.org/en/journals/journalissues/rahj2020Chemical Engineerin

Modification of layered double hydroxides using first-row transition metals for superior UV-Vis-NIR absorption and the influence of the synthesis method used

Layered double hydroxides (LDHs) with high and tailorable UV-Vis-NIR absorption were prepared through transition metal (TM) modification. The synthesis method used and amount of TM present were found to influence the UV-Vis- NIR absorption intensity, -range, and the optical bandgap.https://chemrxiv.orghj2020Chemical Engineerin

Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b

We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society

Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society

Temperature effects on the dissolution-precipitation synthesis of hydrocalumite

The influence of temperature on the balance of formation between katoite and hydrocalumite (HC) was investigated. The conversion to HC could be increased by providing enough thermal energy to the reaction. Favourable reaction conditions for HC formation were reached at 60 C. The rate of reaction to HC and katoite could be increased at 80 C, although the formation of katoite seemingly remained low in comparison to HC formation. At 90 C an increase in katoite and decrease in HC formation was observed indicating the decomposition point of HC.https://aip.scitation.org/journal/apcam2020Chemical Engineerin

Temperature effects on the dissolution-precipitation synthesis of hydrocalumite

The influence of temperature on the balance of formation between katoite and hydrocalumite (HC) was investigated. The conversion to HC could be increased by providing enough thermal energy to the reaction. Favourable reaction conditions for HC formation were reached at 60 C. The rate of reaction to HC and katoite could be increased at 80 C, although the formation of katoite seemingly remained low in comparison to HC formation. At 90 C an increase in katoite and decrease in HC formation was observed indicating the decomposition point of HC.https://aip.scitation.org/journal/apcam2020Chemical Engineerin

Green synthesis of hydrocalumite (CaAl-OH-LDH) from Ca(OH)(2)and Al(OH)(3) and the parameters that influence its formation and speciation

Hydrocalumite is a layered double hydroxide (LDH) that is finding increased application in numerous scientific fields. Typically, this material is produced through environmentally polluting methods such as co-precipitation, sol-gel synthesis and urea-hydrolysis. Here, the hydrothermal green (environmentally friendly) synthesis of hydrocalumite (CaAl-OH) from Ca(OH)2 and Al(OH)3 in water and the parameters that influence its formation are discussed. The parameters investigated include the reaction temperature, reaction time, molar calcium-to-aluminium ratio, the morphology/crystallinity of reactants used, mixing and the water-to-solids ratio. Hydrocalumite formation was favoured in all experiments, making up between approximately 50% and 85% of the final crystalline phases obtained. Factors that were found to encourage higher hydrocalumite purity include a low water-to-solids ratio, an increase in the reaction time, sufficient mixing, the use of amorphous Al(OH)3 with a high surface area, reaction at an adequate temperature and, most surprisingly, the use of a calcium-to-aluminium ratio that stoichiometrically favours katoite formation. X-ray diffraction (XRD) and Rietveld refinement were used to determine the composition and crystal structures of the materials formed. Scanning electron microscopy (SEM) was used to determine morphological differences and Fourier-transform infrared analysis with attenuated total reflectance (FTIR-ATR) was used to identify possible carbonate contamination, inter alia. While the synthesis was conducted in an inert environment, some carbonate contamination could not be avoided. A thorough discussion on the topic of carbonate contamination in the hydrothermal synthesis of hydrocalumite was given, and the route to improved conversion as well as the possible reaction pathway were discussed.This research was funded by Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (THRIP) administered by the Department of Trade and Industry, South Africa, (grant number THRIP/133/31/03/2016). The APC was funded by the University of Pretoria, South Africa.Techsparks (Pty) Ltd, the Technology and Human Resources for Industry Programme (THRIP) and the University of Pretoria, South Africa.http://www.mdpi.com/journal/crystalspm2021Chemical Engineerin

Preparation of photoactive transition-metal layered double hydroxides (LDH) to replace dye-sensitized materials in solar cells

This work highlights the use of Fe-modified MgAl-layered double hydroxides (LDHs) to replace dye and semiconductor complexes in dye-sensitized solar cells (DSSCs), forming a layered double hydroxide solar cell (LDHSC). For this purpose, a MgAl-LDH and a Fe-modified MgAl LDH were prepared. X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy were used to analyze the structural properties, morphology, and success of the Fe-modification of the synthesized LDHs. Ultraviolet-visible (UV-Vis) absorption spectroscopy was used to analyze the photoactive behavior of these LDHs and compare it to that of TiO2 and dye-sensitized TiO2. Current-voltage (I–V) solar simulation was used to determine the fill factor (FF), open circuit voltage (VOC), short circuit current (ISC), and efficiency of the LDHSCs. It was shown that the MgFeAl-LDH can act as a simultaneous photoabsorber and charge separator, effectively replacing the dye and semiconductor complex in DSSCs and yielding an efficiency of 1.56%.http://www.mdpi.com/journal/materialsam2021Chemical Engineerin