Ferric phosphate for the production of LiFePO4 cathodes in lithium ion batteries is commonly obtained by a precipitation reaction between water-soluble iron species and orthophosphates. The kinetics and purity of the precipitate are dependent on its solubility. For this reason and inconsistencies in the solubility data, the solubility of ferric phosphate was currently investigated. The solid dispersed in water was characterized by TGA/DTGA, SEM, EDX and XRD analyses, revealing that it was amorphous FePO4·~1.6H2O. The solubility experiments were carried out in the pH ~1 to 10 at approximately 278, 298, 318 and 338 K and ionic strength lower than approximately 0.5 mol L−1. The solubility was determined on the basis of measurements of equilibrium concentration of soluble phosphorus by spectrophotometry. pH-solubility diagrams were made by solving a system of nonlinear algebraic equations involving a set of eight reactions at equilibrium. By combining this equilibrium model and an optimization method, the negative logarithm of the solubility product and the enthalpy of formation of amorphous FePO4·~1.6H2O were found to be 22.89 ± 0.81 and − 1918.90 ± 22.92 kJ mol−1 (α = 0.05 and ν ≥ 16). The results demonstrate no evidence of a statistically significant difference between the solubility of amorphous hydrated and amorphous anhydrous FePO4 (p = 0.501), but the solubility of both were greater than that of crystalline FePO4·2H2O (p < 0.001). The difference between the enthalpy of formation of amorphous FePO4·~1.6H2O and crystalline FePO4·2H2O was statistically significant (p = 0.019).
The solubilities of furosemide and pentoxifylline in aqueous low alcohol solutions, such as ethanol, isopropanol, methanol, and n-propanol, were experimentally obtained with the use of an isothermal shake-flask process. As stated by an XRD analysis, the crystals of furosemide and pentoxifylline did not exhibit any solvation or transition. Solubility data correlation was performed through using two models, namely modified van't Hoff-Jouyban-Acree and Jouyban-Acree. This resulted in average relative deviations of ≤6.02% and average-root-square deviations of ≤16.5 × 10−3. The approach of extended Hildebrand solubility (EHSA) was also worked to analyze the equilibration solubility data at 298.15 K, resulting in average relative deviation values of no higher than 6.66%. An inversion of the Kirkwood-Buff theory was further involved to investigate the preferential solvation of the two drugs. Blends with water concentrated compositions exhibited positive magnitudes for the pentoxifylline preferential solvation parameter, indicating that alcohol preferentially solvated pentoxifylline. Alcohols exhibited preferential solvation of furosemide within the entire alcohol composition ranges. The intermolecular interactions of pentoxifylline/furosemide with solvents were examined using molecular dynamics simulation, e.g. radial distribution function and solvation free energy, indicating the leading contribution of hydrogen bonding interactions of solute-solvent and solvent-solvent to the pentoxifylline and furosemide solubility in blended solvents. An examination of the entropy-enthalpy compensation revealed that the pentoxifylline crystal dissolution in blends was an entropy-driven and enthalpy process within alcohol-rich region. The enthalpy-driven compensation mechanism was demonstrated by the positive slopes of ΔsolH3,1+2o versus ΔsolG3,1+2o curves for furosemide, which encompassed the entire composition range of alcohols.
A physics-informed model for the dynamic viscosity of deep eutectic solvents (DES) is developed, requiring only SMILES molecular representations as input. The model is grounded in Eyring's transition-state theory for viscous flow and decomposes the activation Gibbs energy into five physically distinct contributions: hole formation (Fürth theory), hydrogen-bond network reorganization, electrostatic cage escape, dispersion interactions, and molecular shape effects. Each contribution is quantified through molecular descriptors computed from SMILES using the open-source RDKit library, with composition-dependent mixing rules derived from the underlying physics. The 45 universal parameters are calibrated against a curated database of 3440 experimental viscosity data points spanning 237 chemically diverse DES systems (84 hydrogen-bond acceptors, 94 hydrogen-bond donors), covering temperatures from 278 to 378 K and viscosities from 1.3 to 85,000 mPa·s. The model achieves R2 = 0.77 and RMSE = 0.35 log₁₀(mPa·s), with 88% of predictions within ±0.5 log units. Leave-one-component-out cross-validation demonstrates robust extrapolation to completely unseen molecular species (74% with RMSE <0.5). Physical soundness is confirmed: calibrated parameters reproduce experimental activation energies (R2 = 0.63), coefficient signs match theoretical expectations, and the hydrogen-bond contribution correctly ranks known DES families. An open-access predictive tool is provided.
This work presents a systematic thermodynamic investigation of the equilibrium solubility of tributyl phosphate (TBP) in aqueous electrolyte systems. The solubility of TBP was measured in chloride solutions (LiCl, NaCl, MgCl2), hydrochloric acid, and sodium hydroxide over a wide concentration range, with dissolved TBP concentrations in the aqueous phase quantified using gas chromatography–mass spectrometry (GC–MS). The results show that TBP solubility is strongly dependent on electrolyte composition and ionic strength. In neutral salt solutions, increasing electrolyte concentration leads to a pronounced salting-out effect, following the order Mg2+ > Na+ > Li+. In acidic media, a non-monotonic (U-shaped) dependence of solubility on acid concentration is observed, reflecting the competition between salting-out and specific solute–acid interactions. In alkaline solutions, TBP solubility decreases monotonically with increasing NaOH concentration, mainly due to enhanced ionic strength effects. The experimental data were analyzed using thermodynamic and semi-empirical models, including the Setschenow equation and a modified Langmuir-type correlation. In addition, an additive model was proposed to quantitatively describe the combined effects of salting-out and complexation in acidic systems. The proposed models show good agreement with experimental data and provide a thermodynamic framework for describing TBP solubility behavior in complex electrolyte environments. The established thermodynamic correlation was further used to evaluate the trend of TBP dissolution loss during the extraction process, confirming its applicability in complex liquid-liquid systems. This work provides a quantitative framework for understanding solute-electrolyte interactions and offers useful insights for the thermodynamic modeling of solubility and related phase behavior of organophosphorus extractants in electrolyte solutions.
