The calculation of the solubility of metal hydroxides, oxide-hydroxides, and oxides, and their visualisation in logarithmic diagrams

A Unified Charge Storage Mechanism to Rationalize the Electrochemical Behavior of Quinone-Based Organic Electrodes in Aqueous Rechargeable Batteries

Due to their eco-sustainability and versatility, organic electrodes are promising candidates for large-scale energy storage in rechargeable aqueous batteries. This is notably the case of aqueous hybrid batteries that pair the low voltage of a zinc anode with the high voltage of a quinone-based (or analogue of quinone-based) organic cathode. However, the mechanisms governing their charge-discharge cycles remain poorly understood and are even a matter of debate and controversy. No consensus exists on the charge carrier in mild aqueous electrolytes, especially when working in an electrolyte containing a multivalent metal cation such as Zn2+. In this study, we comprehensively investigate the electrochemical reactivity of two model quinones, chloranil, and duroquinone, either diluted in solution or incorporated into carbon-based composite electrodes. We demonstrate that a common nine-member square scheme proton-coupled electron transfer mechanism allows us to fully describe and rationalize their electrochemical behavior in relation to the pH and chemical composition of the aqueous electrolyte. Additionally, we highlight the crucial role played by the pKas associated with the reduced states of quinones in determining the nature of the charge carrier that compensates for the negative charges reversibly injected in the active material. Finally, contrary to the widely reported findings for Zn/organic batteries, we unequivocally establish that the predominant solid-state charge carriers in Zn2+-based mild aqueous electrolytes are not multivalent Zn2+ cations but rather protons supplied by the weakly acidic hexaaqua metal ions (i.e., [Zn(H2O)6]2+]).

Green Epoxidation of Olefins with ZnxAl/MgxAl-LDH Compounds: Influence of the Chemical Composition

This contribution concerns the effect of the chemical composition of the brucite-type layer of bi-cationic LDH materials ZnxAl and MgxAl (x = 2–5) and tri-cationic LDH MgyZnzAl (y + z = 4, y = 1, 2, 3) on their catalytic activity for olefin epoxidation with H2O2 in the presence of acetonitrile. LDH materials were prepared by the standard method of co-precipitation at constant pH 10, using an aqueous solution of the corresponding metal nitrates and a basic solution containing NaOH and Na2CO3. The fresh LDHs were calcined to yield the corresponding mixed oxides and then the recovery of the LDH structure by hydration of the mixed oxides was performed. The resulting samples were characterized by AAS, XRD, DRIFT, DR-UV–Vis, BET and determination of basic sites. The results of the catalytic tests for olefin epoxidation were well correlated with the basicity of the samples, which was in turn related to the M2+/Al3+ ratio and the electronegativity of different bivalent metals in the brucite-type layer.

Enhancement of aragonite mineralization with a chelating agent for CO2 storage and utilization at low to moderate temperatures

Among the CaCO3 polymorphs, aragonite demonstrates a better performance as a filler material in the paper and plastic industries. Despite being ideal from the environmental protection perspective, the production of aragonite particles via CO2 mineralization of rocks is hindered by the difficulty in achieving high production efficiencies and purities, which, however, can be mitigated by exploiting the potential ability of chelating agents on metal ions extraction and carbonation controlling. Herein, chelating agent N,N-dicarboxymethyl glutamic acid (GLDA) was used to enhance the extraction of Ca from calcium silicate and facilitate the production of aragonite particles during the subsequent Ca carbonation. CO2 mineralization was promoted in the presence of 0.01-0.1 M GLDA at ≤ 80 °C, with the maximal CaCO3 production efficiency reached 308 g/kg of calcium silicate in 60 min using 0.03 M GLDA, which is 15.5 times higher than that without GLDA. In addition, GLDA showed excellent effects on promoting aragonite precipitation, e.g., the content of aragonite was only 5.1% in the absence of GLDA at 50 °C, whereas highly pure (> 90%, increased by a factor of 18) and morphologically uniform aragonite was obtained using ≥ 0.05 M GLDA under identical conditions. Aragonite particle morphologies could also be controlled by varying the GLDA concentration and carbonation temperature. This study proposed a carbon-negative aragonite production method, demonstrated the possibility of enhanced and controlled aragonite particle production during the CO2 mineralization of calcium silicates in the presence of chelating agents.

Removal of Paramagnetic Ions Prior to Analysis of Organic Reactions in Aqueous Solutions by NMR Spectroscopy

This article describes a method for improving ¹H NMR spectra of aqueous samples containing paramagnetic metals by precipitation of metal cations with a variety of counteranions. The addition of hydroxide, phosphate, carbonate, and arsenate to solutions of transition metals such as Fe²⁺ and Mn²⁺ can reduce line broadening and improve the ability of a spectrometer to lock on the signal of deuterium. The method is most effective under strongly alkaline conditions, and care must be taken to observe whether the organic substrates undergo side reactions or are themselves removed from solution upon addition of the precipitating salts. As a demonstration of the practical value of the method, we show that NMR spectroscopy can be used to monitor the transition-metal-mediated hydrolysis of glycylglycine (Gly₂).

Solubility Data of Potential Salts in the MgO-CaO-SO2-H2O-O2 System for Process Modeling

This review studies unwanted precipitation reactions, which can occur in SO2 absorption processes using a magnesium hydroxide slurry. Solubility data of potential salts in the MgO-CaO-SO2-H2O system are evaluated. The reviewed data can serve as a reliable basis for process modeling of this system used to support the optimization of the SO2 absorption process. This study includes the solubility data of MgSO3, MgSO4, Mg(OH)2, CaSO3, CaSO4, and Ca(OH)2 as potential salts. The solubility is strongly dependent on the state of the precipitated salts. Therefore, this review includes studies on the stability of different forms of the salts under different conditions. The solubility data in water over temperature serve as a base for modeling the precipitation in such system. Furthermore, influencing factors such as pH value, SO2 content and the co-existence of other salts are included and available data on such dependencies are reviewed. Literature data evaluated by the International Union of Pure and Applied Chemistry (IUPAC) are revisited and additional and newer studies are supplemented to obtain a solid base of accurate experimental values. For temperatures higher than 100 °C the available data are scarce. For a temperature range from 0 to 100 °C, the reviewed investigations and data provide a good base to evaluate and adapt process models for processes in order to map precipitations issues accurately.

YAG:Ce3+ Phosphor: From Micron-Sized Workhorse for General Lighting to a Bright Future on the Nanoscale

The renowned yellow phosphor yttrium aluminum garnet (YAG) doped with trivalent cerium has found its way into applications in many forms: as powder of micron sized crystals, as a ceramic, and even as a single crystal. However, additional technological advancement requires providing this material in new form factors, especially in terms of particle size. Where many materials have been developed on the nanoscale with excellent optical properties (e.g., semiconductor quantum dots, perovskite nanocrystals, and rare earth doped phosphors), it is surprising that the development of nanocrystalline YAG:Ce is not as mature as for these other materials. Control over size and shape is still in its infancy, and optical properties are not yet at the same level as other materials on the nanoscale, even though YAG:Ce microcrystalline materials exceed the performance of most other materials. This review highlights developments in synthesis methods and mechanisms and gives an overview of the state of the art morphologies, particle sizes, and optical properties of YAG:Ce on the nanoscale.

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.

Comparison of the effect of transition metal modification on the material properties of quintinite synthesised using co-precipitation under the same conditions.