Temperature-dependent solubility transition of Na₂SO₄ in water and the effect of NaCl therein: solution structures and salt water dynamics

General Aqueous System Simulation through an AI-Embedded Metaverse Chemistry Laboratory

Recent decades have witnessed the rapid development of autonomous laboratories and artificial intelligence, where experiments can be automatically run and optimized. Although human work is reduced, the total time of experimental optimization is still consuming due to limitations of the current ab metaverse framework, which accurately predicts the future state of the system by receiving and analyzing in situ experimental data. To substitute for traditional simulation methods, we designed a physically endorsed deep learning model to predict the future system picture ranging from atomic image to bulk appearance, intensively using the correlations between properties of the system. Through this framework, we studied the general aqueous system, covering 100+ common ionic solutions. We can accurately simulate properties for a general aqueous system as well as predict the time of solvation of ionic compounds ahead of real experiments. In this way, the experiments can be optimized more efficiently without waiting for the end of a bad iteration. We hope our work offers a fresh direction for the digitization of chemical information, enhancing access to and use of experimental data in advancing the field of physical chemistry.

Study of Ion Velocity Effect on the Band Gap of CVD-Grown Few-Layer MoS2

The present work reports on a simple chemical vapor deposition (CVD) technique that employs alkali halide (NaCl) to synthesize high-quality few-layer MoS2 by reducing growth temperature from 850 to 650 °C, and its ion irradiation study for band gap modification. The Raman peak position difference of A1g to E12g of ≈24.5 cm-1 for the synthesized MoS2 corresponds to a few layers (<5 monolayers) of MoS2 on the substrate, as also confirmed by atomic force microscopy (AFM). The optical image shows the continuous distribution of flakes throughout the substrate and the average area of flakes ≈0.2 μm2 as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Swift heavy-ion (SHI) irradiation at 60, 100, and 150 MeV ion energies of 1 × 1012 ions/cm2 ion fluence have been used to modify the band gap in few-layer MoS2. The ions with two different energies are chosen at two sides of the Bragg peak of energy loss curve in such a way as to have the same value of electronic energy loss (Se) but different ion energies to examine the velocity effect for the ion-induced modification. The absorbance peaks for 60 and 150 MeV irradiated samples show the same effect in the band gap modification.

Evaluation of percrystallization coupled with electrodialysis for zero liquid discharge in the pulping industry

We evaluated percrystallization at laboratory scale to determine its suitability as core technology for achieving Zero Liquid Discharge (ZLD) in a Kraft effluent desalination process. Compared with conventional evaporation/crystallization techniques, percrystallization allows to operate at room temperature and with barely pressurized fluids, using relatively unexpensive membranes and vacuum to allow evaporation of aqueous brine solutions. For further comprehension of the technology before experimentation, a computational fluid dynamics model was developed, showing how temperature affects the performance of percrystallization in terms of transmembrane flux. Additionally, we performed experiments with single and double salt solutions (NaCl and NaCl/Na₂SO₄) and concentrated industrial effluent from a Kraft pulp mill (brine from the effluent desalination with electrodialysis). Percrystallization of the concentrated industrial effluent was successfully achieved at laboratory scale, showing no signs of fouling on the membrane surface. However, high energy consumptions (above 3000 kWh/ton of evaporated water) were measured. Theoretical power consumptions of an optimized industrial percrystallization system were therefore computed. Percrystallization showed a more efficient performance compared with similar membrane systems, such as vacuum membrane distillation, but higher energy consumptions than conventional ZLD technologies (mechanical vapor compression), having an estimated energy consumption of around 110-150 kWh/ton of removed water, depending on the feed fluid temperature. Nevertheless, percrystallization could be suitable for ZLD applications where low-cost heating (e.g., solar) is available, since the vacuum energy demand is only 32-140 kWh/ton. Alternatively, it could be applied to low scale processes where the temperature of the solution must remain low (e.g., less than 40 °C).

A study on pyro-hydrometallurgical process for selective recovery of Pb, Sn and Sb from lead dross

This study is to propose a pyro-hydrometallurgical process for recovering Pb, Sn, and Sb from lead dross (LD), incorporating stages of roasting, leaching, and precipitation. The LD, containing 67.2% of Pb, 4.0% of Sn, and 1.4% of Sb, was first roasted at 750 °C for 2 h to oxidise the sulphide metals. Approximately 90% of Pb was oxidised from the first roasting. The LD was second roasted by mixing with 95% H₂SO₄ for sulphatising at 300 °C for 3 h to break the complex oxide structure of the oxyplumboromeite (Pb₂Sb₂O₇). After the two-step roasting process, over 99% of Pb was oxidised and Sb was separated. The calcine obtained was desulphurised by 2 M Na₂CO₃ solution for insoluble PbSO₄ to PbCO₃ for selective leaching. The residue was then leached in 2.5 M HNO₃ at 50 °C for 3 h and over 99% of Pb dissolved into the solution while Sn and Sb remained in the solid residue. The Pb containing solution was neutralised at pH 8 using 2 M Na₂CO₃ and over 99% Pb was precipitated as PbCO₃ and Pb hydroxides. A residue containing Sn and Sb was leached in 7 M NaOH at 95 for 1 h and over 99% Sn was leached selectively. Sn in the solution was precipitated at pH 7 using 2 M H₂SO₄ as SnO₂. Sb was recovered as Sb₂O₃ in solid reside from Sn leaching. The overall recovery rates of Pb, Sn, and Sb from the LD were 99.5%, 95.4%, and 86.3%, respectively. The proposed process is expected to contribute to recycling Pb and other metal values from LD by minimising hazardous waste emissions.

The Structures of ZnCl2-Ethanol Mixtures, a Spectroscopic and Quantum Chemical Calculation Study

We report in this article the structural properties, spectral behavior and heterogeneity of ZnCl₂-ethanol (EtOH) mixtures in a wide-composition range (1:3 to 1:14 in molar ratios), using ATR-FTIR spectroscopy and quantum chemical calculations. To improve the resolution of the initial IR spectra, excess spectroscopy and two-dimensional correlation spectroscopy were employed. The transformation process was suggested to be from EtOH trimer and EtOH tetramer to EtOH monomer, EtOH dimer and ZnCl₂-3EtOH complex upon mixing. The theoretical findings showed that increasing the content of EtOH was accompanied with the flow of negative charge to ZnCl₂. This led to reinforcement of the Zn←O coordination bonds, increase of the ionic character of Zn‒Cl bond and weakening and even dissociation of the Zn‒Cl bond. It was found that in some of the ZnCl₂-EtOH complexes optimized at the gas phase or under the solvent effect, there existed hydroxyls with a very special interactive array in the form of Cl‒Zn⁺←O‒H^…Cl^-, which incredibly red-shifted to wavenumbers <3000 cm^-1. This in-depth study shows the physical insights of the respective electrolyte alcoholic solutions, particularly the solvation process of the salt, help to rationalize the reported experimental results, and may shed light on understanding the properties of the deep eutectic solvents formed from ZnCl₂ and an alcohol.

Hygroscopic properties of sodium and potassium salts as related to saline mineral dusts and sea salt aerosols

Mineral dust, soil, and sea salt aerosols are among the most abundant primary inorganic aerosols in the atmosphere, and their hygroscopicity affects the hydrological cycle and global climate. We investigated the hygroscopic behaviors of six Na- and K-containing salts commonly found in those primary organic aerosols. Their hygroscopic growths as a function of relative humidity (RH) agree well with thermodynamic model prediction. Temperature dependence of deliquescence RH (DRH) values for five of those salts was also investigated, which are comparable to those in literature within 1%-2% RH, most showing negative dependence on temperature. Hygroscopic growth curves of real-world soil and sea salt samples were also measured. The hygroscopic growths of two more-hydroscopic saline soil samples and of sea salt can be predicted by the thermodynamic model based on the measured water-soluble ionic composition. The substantial amounts of water-soluble ions, including Na⁺ and K⁺, in saline soil samples imply that even nascent saline soil samples are quite hygroscopic at high-RH (>80%) conditions. For three less-hygroscopic dust samples, however, measurements showed higher water uptake ability than that predicted by the thermodynamic model. The small amount of water taken up by less-hygroscopic dust samples suggests that dust particles might contain thin layers of water even to very low RH. The results of this study provide a comprehensive characterization of the hygroscopicity of Na- and K-containing salts as related to their roles in the hygroscopic behaviors of saline mineral dusts and sea salt aerosols.

Aqueous size-exclusion chromatography of polyelectrolytes on reversed-phase and hydrophilic interaction chromatography columns

The size-exclusion separation of a water-soluble polyelectrolyte polymer, sodium polystyrene sulfonate (NaPSS), was demonstrated on common reversed-phase (C_18, C₄, phenyl, and cyano) and hydrophilic interaction chromatography (HILIC) columns. The effect of common solvents - acetonitrile (ACN), tetrahydrofuran (THF), and methanol (MeOH), used as mobile phase modifiers - on the elution of NaPSS and the effect of column temperature (within a relatively narrow range corresponding to typical chromatographic conditions, i.e., 10 °C-60 °C) on the partition coefficient, K_SEC, were also investigated. Non-size-exclusion chromatography (non-SEC) effects can be minimized by the addition of an electrolyte and an organic modifier to the mobile phase, and by increasing the column temperature (e.g., to 50 °C or 60 °C). Strong solvents such as THF and ACN are more successful in the reduction of such effects than is the weaker solvent MeOH. The best performance is seen on medium polarity and polar stationary phases, such as cyanopropyl- and diol-modified silica (HILIC), where the elution of the NaPSS polyelectrolyte is by a near-ideal SEC mechanism. Hydrophobic stationary phases, such as C₁₈, C₄, and phenyl, require a higher concentration of a strong solvent modifier (THF) in the mobile phase to reduce non-SEC interactions of the solute with the stationary phase.