Search Results (7)

In recent years, noticeable progress has been made in the development of alternative extraction systems characterized by greater sustainability. In this context, deep eutectic solvents (DESs) have emerged as a promising alternative to the conventional solvents commonly used in metal extraction. This work focuses on investigating the extraction of lanthanum in an aqueous solution of sulfuric acid using a deep eutectic solvent, employing molecular dynamics simulations (MD). The structural characteristics of the solvent and its interactions with the components of the aqueous solution are explored. In this study, tetraethylammonium bromide (TEABr) is combined with ethylene glycol (EG) to form a DES, in which sodium cyanide (NaCN) is subsequently solubilized. According to the results obtained from the MD simulation, the primary interactions in the DESs are established through hydrogen bonds between the bromine and the hydrogens of the methyl group of tetraethylammonium at 3.5 Å, as well as between the bromine and the hydrogens of the methylene group of ethylene glycol at 3.5 Å. Similarly, the main interactions between the binary DES and sodium cyanide occur through the hydrogens of the hydroxyl group of EG and the carbon of cyanide at 1.7 Å, and between the oxygen of the hydroxyl group of EG and the sodium at 2.5 Å. In the acidic solution, the primary interaction is highlighted between the lanthanum ion and the oxygen of the bisulfate at 2.8 Å. Additionally, it is observed that the interaction between the DES and the aqueous solution occurs between the lanthanum and the oxygen of the hydroxyl group of EG, as well as between the lanthanum and the carbon of cyanide at 4.4 Å. It is important to note that, when increasing the temperature from 25 to 80 °C, the interaction distance between the lanthanum and the carbon of cyanide decreases to 2.4 Å, suggesting a possible correlation with the increase in lanthanum extraction, as experimentally observed. Overall, this study underscores the importance of considering the fundamental structural interactions of the DES with the lanthanum acid solution, providing an essential theoretical basis for future experimental investigations. Full article

Quantum dots (QDs) have captured the attention of the scientific community due to their unique optical and electronic properties, leading to extensive research for different applications. They have also been employed as sensors for ionic species owing to their sensing properties. Detecting anionic species in an aqueous medium is a challenge because the polar nature of water weakens the interactions between sensors and ions. The anions bicarbonate (HCO₃⁻), carbonate (CO₃²⁻), sulfate (SO₄²⁻), and bisulfate (HSO₄⁻) play a crucial role in various physiological, environmental, and industrial processes, influencing the regulation of biological fluids, ocean acidification, and corrosion processes. Therefore, it is necessary to develop approaches capable of detecting these anions with high sensitivity. This study utilized CdTe QDs stabilized with cysteamine (CdTe-CYA) as a fluorescent sensor for these anions. The QDs exhibited favorable optical properties and high photostability. The results revealed a gradual increase in the QDs’ emission intensity with successive anion additions, indicating the sensitivity of CdTe-CYA to the anions. The sensor also exhibited selectivity toward the target ions, with good limits of detection (LODs) and quantification (LOQs). Thus, CdTe-CYA QDs show potential as fluorescent sensors for monitoring the target anions in water sources. Full article

Graphite bisulfate (GBS) compounds consist of graphite layers intercalated by HSO${}_4^{-}$ ions and H${}_2$SO${}_4$ molecules. Owing to electrostatic interactions with the graphene plane, HSO${}_4^{-}$ ions cause point defects in the graphite’s crystalline structure, while H${}_2$SO${}_4$ molecules are free to move via diffusion in the spaces between the adjacent graphite sheets and segregate to form linear defects. In the present work, we report the results of our investigation using Raman spectroscopy on the temporal evolution of such defects on selected GBS samples over 84 months. Two characteristic lengths correlated with the average distance between defects have been estimated and their evolution with aging was investigated. The results show a decrease in the density of point-like defects after aging, regardless of the pristine structural configuration of the GBS samples, revealing a structural instability. This study can provide significant information for the technological development of industrial processes aimed to produce expanded graphite based on GBS precursors, where the aging of GBS is known to influence the efficiency and quality. Full article

Chlorogenic acid (CQA) is one of phenolics commonly found in higher plants, possessing numerous health-promoting effects on humans. Unfortunately, it is easily degraded/transformed into other substances during extraction. Therefore, its reliable analysis requires a special approach that does not involve high temperatures. This paper presents a very simple method of CQA isolation using the sea sand disruption method with subsequent purification of the extract using the ion-pair solid-phase extraction process, followed by HPLC–DAD detection. It was found that control of the ion pairing reagent concentration and sample pH is crucial to improve purification, and that the best results, with recovery exceeding 98%, were obtained for 0.05 M tetrabutylammonium bisulfate at pH 7 when the ion pairs were formed directly in the extract and eluted from the C18 sorbent using an acidified methanol–water mixture. The practical potential of the developed procedure was verified by using it for CQA isolation from different plants. The approach represents one of the contemporary analytical trends and current advances in the solid phase extraction, in which several sorption extraction techniques are combined to ensure high-quality analytical results. Full article

Carbonic acid is an important species in a variety of fields and has long been regarded to be non-existing in isolated state, as it is thermodynamically favorable to decompose into water and carbon dioxide. In this work, we systematically studied a novel ionic complex [H₂CO₃·HSO₄]⁻ using density functional theory calculations, molecular dynamics simulations, and topological analysis to investigate if the exotic H₂CO₃ molecule could be stabilized by bisulfate ion, which is a ubiquitous ion in various environments. We found that bisulfate ion could efficiently stabilize all the three conformers of H₂CO₃ and reduce the energy differences of isomers with H₂CO₃ in three different conformations compared to the isolated H₂CO₃ molecule. Calculated isomerization pathways and ab initio molecular dynamics simulations suggest that all the optimized isomers of the complex have good thermal stability and could exist at finite temperatures. We also explored the hydrogen bonding properties in this interesting complex and simulated their harmonic infrared spectra to aid future infrared spectroscopic experiments. This work could be potentially important to understand the fate of carbonic acid in certain complex environments, such as in environments where both sulfuric acid (or rather bisulfate ion) and carbonic acid (or rather carbonic dioxide and water) exist. Full article

Mineral carbonation routes have been extensively studied for almost two decades at Åbo Akademi University, focusing on the extraction of magnesium from magnesium silicates using ammonium sulfate (AS) and/or ammonium bisulfate (ABS) flux salt followed by carbonation. There is, however, a need for proper recovery and recirculation of chemicals involved. This study focused on the separation of AS, ABS and aqueous ammonia using different setups of bipolar membrane electrodialysis using both synthetic and rock-derived solutions. Bipolar membranes offer the possibility to split water, which in turn makes it possible to regenerate chemicals like acids and bases needed in mineral carbonation without excess gas formation. Tests were run in batch, continuous, and recirculating mode, and exergy (electricity) input during the tests was calculated. The results show that separation of ions was achieved, even if the solutions obtained were still too weak for use in the downstream process to control pH. Energy demand for separating 1 kg of NH₄⁺ varied in the range 1.7, 3.4, 302 and 340 MJ/kg NH₄⁺, depending on setup chosen. More work must hence be done in order to make the separation more efficient, such as narrowing the cell width. Full article

The separation of ammonium bisulfate (ABS) from ammonium sulfate (AS) in aqueous solutions by monovalent ion selective membranes was studied. Optimised usage of these chemicals is both an important and challenging step towards a more efficient CO₂ mineralisation process route developed at Åbo Akademi University (ÅA). The membranes were placed in a three or five-compartment electrodialysis stack. Silver, stainless steel and platinum electrodes were tested, of which a combination of Pt (anode) and stainless steel (cathode) electrodes were found to be most suitable. Separation efficiencies close to 100% were reached based on ABS concentrations in the feed solution. The tests were performed with an initial voltage of either 10 V–20 V, but limitations in the electrical power supply equipment eventually resulted in a voltage drop as separation proceeded. Exergy calculations for energy efficiency assessment show that the input exergy (electrical power) is many times higher than the reversible mixing exergy, which indicates that design modifications must be made. Further work will focus on the possibilities to make the separation even more efficient and to develop the analysis methods, besides the use of another anode material. Full article