Hoff Equation Research Articles

Solubility study, model correlation and thermodynamics of 3-acetyl-4-hydroxy-2H-chromen-2-one and its chlorinated derivatives in binary solvent mixtures at temperatures from 293.15 to 313.15 K

The solubility of 3-acetyl-4-hydroxy-2H-chromen-2-one (GK-1), 3-acetyl-6-chloro-4-hydroxy-2H-chromen-2-one (GK-2), and 3-acetyl-7-chloro-4-hydroxy-2H-chromen-2-one (GK-3) in binary solvent mixtures of methanol and ethanol was investigated using the gravimetric method over a temperature range of 293.15 K to 313.15 K under atmospheric pressure. Experimental results showed that the mole fraction solubility of GK-1, GK-2, and GK-3 increased with rising temperature and higher co-solvent proportions (0.10 to 0.90 mol fraction). Theoretical mole fraction solubility predictions were made using the Apelblat, Van’t Hoff, Yaws, CNIBS/R-K, and modified Jouyban-Acree models, all of which showed good agreement with the experimental data. Additionally, apparent thermodynamic modeling of GK-1, GK-2, and GK-3 was conducted using the Van’t Hoff equation. The solubility and thermodynamic data obtained are valuable for the processes of production, isolation, separation, and crystallization of these compounds.

Temperature effect on seawater fCO2 revisited: theoretical basis, uncertainty analysis and implications for parameterising carbonic acid equilibrium constants

Abstract. The sensitivity of the fugacity of carbon dioxide in seawater (fCO2) to temperature (denoted υ, reported in % °C−1) is critical for the accurate fCO2 measurements needed to build global carbon budgets and for understanding the drivers of air–sea CO2 flux variability across the ocean. However, understanding and computing υ have been restricted to either using empirical functions fitted to experimental data or determining it as an emergent property of a fully resolved marine carbonate system, and these two approaches are not consistent with each other. The lack of a theoretical basis and an uncertainty estimate for υ has hindered resolving this discrepancy. Here, we develop a new approach for calculating the temperature sensitivity of fCO2 based on the equations governing the marine carbonate system and the van 't Hoff equation. This shows that, to first order, ln (fCO2) should be proportional to 1/tK (where tK is temperature in kelvin), rather than to temperature, as has previously been assumed. This new approach is, to first order, consistent with calculations from a fully resolved marine carbonate system, which we have incorporated into the PyCO2SYS software. Agreement with experimental data is less convincing but remains inconclusive due to the scarcity of direct measurements of υ, particularly above 25 °C. However, the new approach is consistent with field data, performing better than any other approach for adjusting fCO2 by up to 10 °C if spatiotemporal variability in its single fitted coefficient is accounted for. The uncertainty in υ arising from only measurement uncertainty in the main experimental dataset where υ has been directly measured is in the order of 0.04 % °C−1, which corresponds to a 0.04 % uncertainty in fCO2 adjusted by +1 °C. However, spatiotemporal variability in υ is several times greater than this, so the true uncertainty due to the temperature adjustment in fCO2 adjusted by +1 °C using the most widely used constant υ value is around 0.24 %. This can be reduced to around 0.06 % using the new approach proposed here, and this could be further reduced by more measurements. The spatiotemporal variability in υ arises mostly from the equilibrium constants for CO2 solubility and carbonic acid dissociation (K1∗ and K2∗), and its magnitude varies significantly depending on which parameterisation is used for K1∗ and K2∗. Seawater fCO2 can be measured accurately enough that additional experiments should be able to detect spatiotemporal variability in υ and distinguish between different parameterisations for K1∗ and K2∗. Because the most widely used constant υ was coincidentally measured from seawater with roughly global average υ, our results are unlikely to significantly affect global air–sea CO2 flux budgets, but they may have more important implications for regional budgets and studies that adjust by larger temperature differences.

Oiling out and solubility measurement, molecular simulation and thermodynamic properties of d-tagatose in four aqueous binary solvent systems at 283.15 to 323.15 K

Solubility of D-Tagatose in four aqueous binary solvent systems from 278.15 K to 323.15 K was determined using the anti-solvent assisted gravimetric method. The solubility increases with temperature in all four binary solvents, with water, a good solvent, exhibiting a similar trend. In addition, the dissolution process generally follows the ’like dissolves like’ rule. The study indicates that the oiling out occurs when water exhibits a high molar fraction in water + 1-propanol, and water + isopropanol. Furthermore, we study the charge of the molecule using the molecular electrostatic potential surface (MEPS), aiming to analyze the molecular interactions. Then, to explain the dissolution behaviors of D-tagatose, the radial distribution function (RDF) by molecular dynamics simulations (MD) revealed a strong correlation between solute–solvent interactions and solubility, with significant solvent–solvent interactions. The solubility data was correlated using the modified Apelblat equation, Van’t Hoff equation, λh equation, and Jouyban-Acree model, with demonstrating the high consistency in the data. Finally, the thermodynamic properties revealed that the dissolution process of D-Tagatose is endothermic, and entropy-driven based on all positive values for ΔsolHo, ΔsolSo, ΔsolGo.

Kinetic and mechanistic studies on the synthesis of dimethyl carbonate reaction using deep eutectic solvents as catalysts

Dimethyl carbonate (DMC) is extensively utilized in various industries due to its exceptional physical and chemical properties, functioning as an additive in gasoline and an electrolyte solvent in lithium batteries. Among several production methods, the transesterification of propylene carbonate (PC) with methanol (MeOH) is the most efficient and environmentally friendly. This study synthesized various deep eutectic solvents (DESs) using choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and monoethanolamine (MEA) as the hydrogen bond donor (HBD) in molar ratios of 1: n (n = 5, 6, 7, 8). The DESs’ structures were analyzed using Fourier Transform Infrared (FT-IR) spectroscopy, and their melting points were determined via differential scanning calorimetry (DSC). The density, viscosity, and surface tension of the DESs were measured over a temperature range from 318.15 K to 358.15 K. The catalytic effects of four different DESs on PC transesterification with MeOH were investigated, revealing that ChCl-6MEA was the most effective catalyst, prompting its selection for further experiments. Subsequent investigations examined the effects of temperature, MeOH quantity, and catalyst dosage on PC conversion and DMC yield. Additionally, this study explored chemical equilibrium and reaction kinetics through experimental and theoretical approaches. Activity-based chemical equilibrium constants, derived from experimental data, and the van’t Hoff equation elucidated their temperature dependency. A pseudo-homogeneous (PH) model characterized the non-ideal thermodynamic behavior of the liquid phase in reaction kinetics analysis. The Arrhenius equation was employed to delineate the impact of temperature variations on reaction rate constants. Finally, the proposed reaction mechanism for ChCl-6MEA catalyzed transesterification was elucidated and verified through quantum chemistry (QC) calculations.

Directly measuring octanol-air partition ratios using a gas chromatography retention time (GC-RT) method

The octanol-air partition ratio (KOA) is a fundamental property used for screening chemicals for concern, depending on their potential to bioaccumulate and harm living systems. With millions of chemicals used in commerce, unfortunately, less than 800 compounds currently have experimentally measured KOA values due to limitations in traditional measurement techniques. We aimed to develop a direct gas chromatography retention time (GC-RT) method using a custom-packed column, with octanol as the stationary phase, for rapidly measuring KOA. We installed the column into a GC-mass spectrometry system and isothermally measured retention times of 15 volatile organic compounds. We calculated KOA values at experimental temperatures from the retention times and extrapolated the results to values at 25 °C using the Van't Hoff equation. Our directly measured log KOA values at 25 °C spanned 3.66 log units (0.820–4.48). Except for alcohols, our measured values agree with literature log KOA values (root mean square error, RMSE = 0.50). The discrepancy probably arose from differences in how well our method versus the literature methods capture measurement artifacts, specifically, gas-phase adsorption to the octanol phase and hydrogen bonding interactions. This proof-of-concept study demonstrates that our direct GC-RT method is promising for rapidly measuring KOA to support chemical risk assessment.

Determination of the dissolution behavior of 3,4-bis (3-nitrofuran-4-yl) furazan in different solvents using solubility parameters and interaction energy aided analysis

The atmospheric pressure solubility of 3,4-Bis(3-nitrofurazan-4-yl)furoxan(DNTF) in 9 pure solvents (n-propanol, isopropanol, propionic acid, formic acid, carbon tetrachloride, o-xylene, chlorobenzene, anisole, and 1,2-dichloroethane) was studied using dynamic laser monitoring method. Using various equations, including the modified Apelblat equation, Van’t Hoff equation, Yaws model, NRTL model, and Wilson model to establish the relationship between solubility data. The modified Apelblat equation was used to effectively correlate the solubility data, demonstrating a strong correlation between the equation and experimental data. Meanwhile, Hansen solubility parameters analysis and density functional theory calculation of interaction energy were also used to investigate the mechanism of the solubility behavior of DNTF in different solvents. In addition, apparent thermodynamic parameters such as standard dissolution enthalpy, standard dissolution entropy, and standard Gibbs free energy of DNTF in these solvents were calculated. These findings provide valuable insights for future research on DNTF crystallization.

Sc/Y/Ti functionalized N-substituted defective C24 as promising materials for hydrogen storage

Incorporating transition metal atoms and creating porphorin-like N4 cavity are effective strategies for improving the hydrogen storage capability of carbon materials. In this view, we designed and addressed the hydrogen uptake properties of TM4C8N8 (TM = Sc, Y, Ti) cages originating from C24 to overcome TM clustering. The stabilities of three clusters were confirmed by molecular dynamic simulation. Sc4C8N8/Y4C8N8/Ti4C8N8 can bind up to 20/20/36H2 molecules with a higher gravimetric density of 9.35/6.67/15.27 wt%, compared to the goal of 5.5 wt% proposed by the US-DOE. The interaction between H2 molecules and the hosts can be identified as van der Waals attractions. The average binding energies of Sc4C8N8(H2)20/Y4C8N8(H2)20/Ti4C8N8(H2)36 at M06(D3) and PBE(D3) functional are 0.159/0.173/0.128 eV/H2 and 0.139/0.141/0.102 eV/H2, respectively, meeting the desirable range of reversible hydrogen storage. Furthermore, an investigation was conducted on the impact of pressure and temperature on the hydrogen storage capabilities of TM4C8N8 (TM = Sc, Y, Ti). The desorption temperature exhibits a positive correlation with increasing pressure. The realization of hydrogen release at near mild conditions and the reversibility of hydrogen adsorption/desorption cycles were demonstrated using the van't Hoff equation and ADMP-MD simulations, respectively. Compared with the monomer, the hydrogen storage capacities of (TM4C8N8)2 (TM = Sc, Y, Ti) dimers are slightly reduced.

Enhanced hydrogen adsorption properties of Zeolite Templated Carbon via chemical activation: DFT study

In this study, Density Functional Theory (DFT) simulation method was applied to show that hydrogen-storage properties of Zeolite Templated Carbon (ZTC) can be enhanced via chemical activation. Study results calculated via simulation and the Monte Carlo integration technique showed that in comparison to unactivated ZTC, the theoretical specific surface area (SSA) for Zeolite Templated Activated Carbon (ZTAC) increased by 4.79 and 2.13 %, when activated with either Zinc dichloride (ZnCl2) or Potassium Hydroxide (KOH), respectively. In addition, calculation of accessible surface area (ASA) resulted in 7809.40 m2/g and 7611.74 m2/g, correspondingly. Simulations of H2 adsorption revealed that H2 molecules were adsorbed primarily on the concave region of the ZTAC. Also, it was found the that the largest amountof H2 adsorbed molecules on ZTAC activated with either ZnCl2 or KOH were13 and 15, and the average binding energies were 0.184 eV and 0.202 eV, respectively. In this regard, the maximum hydrogen storage capacity obtained in this study was 5.2 wt% (ZTAC-13H2) and 5.95 wt% (ZTAC-15H2) with a volumetric density of 0.065 kg H2/L and 0.074 kg H2/L for the ZTAC activated with either ZnCl2 or KOH. These results are in accordance with the U.S. Department of Energy (DOE) ultimate target by the 2025 year. In addition, thermal stability and desorption temperatures of ZTAC structures were determined via molecular dynamics simulations and through the van’t Hoff equation, showing that hydrogen molecules were easy to desorb at room temperature (T=300 K). These results pose these systems suitable for automotive onboard applications, leading to future research on synthesis techniques of ZTAC materials which certainly require more experimental investigation.

Solubility of sildenafil citrate in acetonitrile + water mixture at different temperatures

ABSTRACT The study involved the determination of the equilibrium mole fraction solubility of sildenafil citrate in aqueous binary mixtures of acetonitrile across a range of temperatures (from 293.15 K to 313.15 K). To represent this data numerically, both linear and non-linear cosolvency models were employed, and their performances were assessed through mean relative deviations or MRD%. Additionally, this study calculated the apparent thermodynamic properties (Gibbs energy, entropy, and enthalpy) for the dissolution processes using the van’t Hoff and Gibbs equations. Moreover, the study determined the density values of sildenafil citrate saturated solutions and presented them through the van’t Hoff equation.

Removal of Moxifloxacin from Aqueous Solutions Using GO/Cr-MOFs.

The composite material, consisting of graphene oxide (GO) and chromium metal-organic frameworks (Cr-MOFs), was successfully synthesized by using a solvothermal method. The organic ligand employed was 2,5-dihydroxyterephthalic acid, while chromium acetate served as the source of the metal. The resulting material underwent characterization through Fourier transform infrared, scanning electron microscopy, and X-ray diffraction techniques. Subsequently, the adsorption capacity of the composite material toward moxifloxacin was evaluated. The results indicated a gradual increase in the moxifloxacin removal rate from GO/Cr-MOFs over time until reaching an equilibrium with a maximum removal rate of 90.4%. Additionally, it was observed that higher temperatures led to a decrease in the adsorption capacity. By incorporating 30 mg of GO/Cr-MOFs into a solution containing 40 ppm of moxifloxacin, the adsorption capacity could be maximized at 222.25 mg/g. Experimental data on MOF adsorption of moxifloxacin were analyzed using pseudo-first-order kinetics (PFO), pseudo-second-order kinetics (PSO), and Langmuir, Freundlich, and Temkin isotherm models for theoretical research purposes. Results showed that the PSO model exhibited a better correlation than the PFO model did. Furthermore, experimental data demonstrated good agreement with the Freundlich isothermal model, suggesting its effectiveness in accurately describing the adsorption process. Henceforth, it can be concluded that chemisorption plays a significant role in removing moxifloxacin by GO/Cr-MOFs. The van't Hoff equation analysis revealed an exothermic and spontaneous nature of moxifloxacin adsorption onto GO/Cr-MOFs. Compared to other materials, the GO/Cr-MOF composite exhibited high potential for applications such as drug removal or related fields.

Equilibrium Solubility of Sulfadiazine in (Acetonitrile + Ethanol) Mixtures: Determination, Correlation, Dissolution Thermodynamics, and Preferential Solvation

The equilibrium solubility of sulfadiazine (SD, 3) in several {acetonitrile (MeCN) + ethanol (EtOH)} mixtures at nine temperatures from T/K = (278.15 K to 318.15) has been determined by following the shake flask method. SD solubility increased with temperature-arising as well as with the MeCN proportion-increasing in the mixtures. Thus, x3 increased from 7.74 × 10−5 in neat EtOH to 6.20 × 10−4 in neat MeCN at T/K = 298.15. SD solubility was adequately correlated with a second-order multivariate equation as function of both mixtures composition and temperature. Moreover, two models including the Jouyban–Acree and Jouyban–Acree–van’t Hoff models were applied to mathematical SD solubility data modeling in solvent mixtures. The accuracy of each model is investigated by the mean relative deviations (MRD%) of the back-calculated solubility. A full predictive model was provided by training the Jouyban–Acree–van’t Hoff model with only seven experimental solubility data which provided excellent predictions with the MRD% of 3.7 %. All used models show a low MRD% values (< 4.0 %) for the calculated data indicating a good correlation of SD solubility data with the given mathematical models. By means of the van’t Hoff and Gibbs equations, the apparent thermodynamic quantities relative to SD dissolution and mixing processes, namely Gibbs energies, enthalpies, and entropies, were calculated and reported. Apparent dissolution quantities of SD were positive in all cases indicating endothermic and entropy-driven behaviors. A non-linear enthalpy–entropy relationship was observed for SD in the plot of SD dissolution enthalpy vs. Gibbs energy. Observed trend exhibits negative slope in the composition from neat EtOH to the mixture of 0.05 in mass fraction of MeCN indicating entropy-driving mechanism for this SD transfer process. Moreover, variant but positive slopes were found in the composition interval of 0.05 < w1 < 1.00 indicating enthalpy-driving mechanism for these SD transfer processes. Furthermore, the preferential solvation of SD by MeCN or EtOH was analyzed by using the inverse Kirkwood–Buff integrals. Thus, SD is preferentially solvated by EtOH molecules in EtOH-rich mixtures but preferentially solvated by MeCN in MeCN-rich mixtures. In this way, this research expands the literature investigations about the solubility of SD in some non-aqueous cosolvent mixtures conformed by MeCN and other alcohols.

Nonlinear three-dimensional modeling for encapsulated microbubble dynamics subject to ultrasound

Encapsulated microbubbles (EMBs) stabilized by thin coatings have been used as contrast agents for ultrasound sonography as well as having been demonstrated as a promising new technology for targeted drug delivery. The dynamics of EMBs is three-dimensional (3D) because EMBs within micro-vessels inevitably interact with boundaries, but the theoretical and numerical studies are limited to spherical, weakly non-spherical, and/or axisymmetric EMBs. Here, we have developed physical, mathematical, and numerical models for nonlinear 3D EMB dynamics. The liquid flow is evaluated using the boundary integral method. The EMB coating is modeled as a thin viscoelastic shell including stretching, bending, and shear effects and simulated using the finite element method. These models are coupled through the kinematic and dynamic boundary conditions at the interface. The model is in good agreement with the Hoff equation for spherical EMBs and the asymptotic theory for weakly non-spherical deformation of EMBs. Using this model, a numerical study for EMB dynamics near a rigid boundary subject to an ultrasonic wave is performed. The migration, non-spherical oscillation, resonant oscillation, and jetting of EMBs are displayed and analyzed systematically. If the ultrasound wave is strong, a high-speed liquid jet forms at the final stage of the collapse, orientated between the directions of the wave and toward the wall. The EMB jet is weaker and slower and has less momentum, as the non-spherical deformation of the coating and the jetting are suppressed by the viscoelastic property of the coating. If the ultrasound is not strong, the EMB remains spherical for many cycles of oscillation but the EMB undergoes resonant oscillation and becomes significantly non-spherical after several oscillation cycles, when the wave frequency is equal to its natural frequency. The numerical capability has the potential to be developed for the optimization of sonography or drug delivery.

Microstructure and hydrogenation/dehydrogenation properties of ball-milled PrMg12/Ni alloy powders

Amorphous and nanocrystalline PrMg12 is ball-milled with 30 wt% Ni powder. The impact of ball milling time on the thermodynamics and kinetics of hydrogen storage in this alloy is systematically studied. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the phase composition and microstructure. The result shows that the microstructure of PrMg12+30 wt%Ni alloy is predominantly amorphous and nanocrystalline. Prior to hydrogen absorption, the primary phases were identified as PrMg12, Ni and Mg2Ni. Following hydrogenation, these phases transform into MgH2 and Mg2NiH4. Pressure-composition-temperature (PCT) curves and kinetic data were acquired using a Sieverts apparatus. The thermodynamic and kinetic parameters are calculated by combining Van't Hoff equation, JMAK model and Arrhenius equation. The effect of ball milling time on the enthalpy and entropy changes of hydrogen desorption was found to be negligible. Notably, the activation energy for dehydrogenation reached a minimum value of 79.86 kJ/mol after 10 h of ball milling.

Reversible hydrogen storage with Na-modified Irida-Graphene: A density functional theory study

Two-Dimensional carbon-based materials as a potential hydrogen storage medium have attracted great attention. In this study, various key aspects such as structure, electronic properties, stability, and hydrogen storage performance of Na-modified Irida-Graphene (IG) were thoroughly investigated using density functional theory (DFT) calculation methods. The calculation results show that the binding energy of Na atoms with the substrate is 1.51 eV, far exceeding the cohesive energy. The AIMD results reflect the good thermal stability of the model. One Na atom can adsorb up to 5H2 molecules. The IG loaded with eight Na atoms on both sides can adsorb 32H2 molecules, achieving a hydrogen storage capacity of 7.82 wt%, far exceeding the US DOE target of 5.5 wt%. The calculated Van ’t Hoff equation indicates a desorption temperature of 248 K for the model. Moreover, reversible hydrogen storage can be achieved at medium to low pressures, with desorption temperatures ranging from 285 K to 417 K. These results suggest that Na-Modified IG models are candidate materials for reversible hydrogen storage under near-ambient conditions.

Spectrophotometric analysis and mechanistic insights investigation of a developed CT complex as colorimetric real-time sensing performance towards Fe2+ in aqueous medium

A newly developed charge transfer complex (CTC) is explored for colorimetric real-time sensing behavior towards the Fe2+ ion, as a highly selective real-time colorimetric chemosensor material. The synthesized and characterized CTC / P1, [(2HP)+(SA)−] is cheap, remarkably distinctive, and simple to manufacture. Beyond the exposure limitations, iron is also the most common cofactor in enzyme reactions, which is, therefore a crucial part of life. However, too much or not enough iron leads to anemia, liver damage, cancer, Alzheimer's disease, and Parkinson's disease. In this report, unusual sensing capacity has been reported with a relatively low detection limit of 1.247 ppb for Fe2+ ions in aqueous medium, which was lowest at 1.267 ppb in previous reports of CTC sensors. By using a static quenching process, the incredible sensing behavior of this material as a chemosensor was determined. Colorimetric sensing behavior in real-time has also been observed. The complex has been described using a variety of methods, including UV-visible and FTIR spectroscopy. In FTIR spectra, the CTC (P1) showed a change in wavenumber when compared to its reactants. Furthermore, the complex's stoichiometry was measured using UV-visible spectroscopy by taking mixture with an equimolar ratio using the straight-line approach known as the Benesi-Hildebrand equation, which was found to be 1:1. Oscillator strength (f), transition dipole moment (μEN), molar extinction coefficient (εCT), energy of interaction (ECT), and stability constant (KCT) were among the thermodynamic and physical characteristics studied. Van't Hoff's equation was used to compute other parameters such as Gibbs free energy (G°), absorptivity coefficient (ε), Resonance energy (RN), etc. [O+—H……O−] hydrogen bonding was used to depict the interaction between reactants (salicylic acid and 2-hydroxypyridine). The stability of the P1 as a function of temperature is demonstrated through TG/DTA analysis.

Evaluation of hydrogen storage performance of Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy using calorimetric technique

The features of phase transformations during interaction of BCC-type Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy (HEA) with hydrogen and the accompanying thermal effects have been examined using the Tian-Calvet calorimetric technique. The alloy was produced by the pendent drop melt extraction method in the form of microfibers and then coated with a thin layer of palladium to eliminate the preliminary high-temperature activation and enable first hydrogenation at room temperature. Two reaction stages were distinguished on the measured heat emission curves. Using XRD data, these stages were attributed to the formation of a BCC-type hydrogen solid solution and a phase transition to FCC-type dihydride phase. Recorded values of the reaction enthalpy decrease in absolute terms from 145 kJ/mol H2 (dilute solid solution) to 73–77 kJ/mol H2 (BCC→FCC) and to 20 kJ/mol H2 (H solution in FCC dihydride). The overall heat emission of the entire process as a whole is 110 kJ/ mol H2. The course of the dehydrogenation process depends strongly on the applied temperature and at 493 K results in the formation of a BCT-type monohydride, which was not detected during hydrogenation. The detailed calorimetric data obtained here significantly change the previously existing ideas about thermal effects during this type HEAs hydrogenation, based on calculations using the Van't-Hoff equation. The reported findings are of special importance for various hydrogen related applications of HEAs

On physical meaning of van't Hoff equation and its applicability in chromatography

The van't Hoff equation is a widely used tool to study adsorption thermodynamics in chromatography. Recent experimental data and some theoretical arguments questioned the accuracy of thermodynamic characteristics determined by using this equation. The present report addresses these concerns and shows that if certain requirements are satisfied, the van't Hoff analysis provide reliable results. These requirements include isothermality of the column not perturbed by the percolation of the mobile phase, mass transfer kinetics allowing sufficient proximity to equilibrium, pressure below 200 bar for low molecular weight compounds and below 50 bar for macromolecules, and knowledge of the phase ratio at all experimental temperatures to allow accurate conversion of the retention factor to the equilibrium constant. Physical meaning of adsorption enthalpy and entropy obtained by means of the van't Hoff analysis particularly in the case of heterogeneous adsorbents is discussed and recommendations on how to perform experiments to obtain reliable results are given.

Thermally Driven Catch-and-Release of CoCl2.

A heat-driven catch-and-release strategy for CoCl2 capture is described. It is based on the use of an immobilized neutral dicyclohexylacetamide-based receptor L supported on polystyrene (PS-L). An X-ray diffraction analysis of a single crystal of L·CoCl2 revealed an ion-pair complex comprising a hexacoordinated cobalt cation [L·Co]2+ and a tetrachlorocobaltate anion [CoCl4]2-. Temperature dependent binding was seen, as inferred from UV-vis spectroscopic studies. Fits to the van't Hoff equation yielded values of ΔH° = 12.4 kJ/mol and ΔS° = 56.0 J/K·mol for L + CoCl2, and ΔH° = 16.5 kJ/mol and ΔS° = 85.0 J/K·mol for PS-L + CoCl2 in 95% ethanol. Consequently, cobalt capture and release are mediated by heating and cooling, respectively. The material PS-L exhibits a preference for binding cobalt over manganese and nickel as inferred from Langmuir-Freundlich isotherm analyses that revealed binding constants of KLF = 88.5 M-1 for CoCl2, 52.7 M-1 for MnCl2, and 49.7 M-1 for NiCl2. In a simulated ion mixture containing equimolar CoCl2, MnCl2, and NiCl2, ICP-MS analyses served to confirm that cobalt was selectively enriched to 52 mol % (from an initial level of ca. 32 mol %) after one catch-and-release cycle and 76.6% after three cycles. Our experimental results were validated by density functional theory calculations, which also show stronger binding of Co over Mn and Ni to L.

Thermodynamic properties of β-HMX in binary mixed solvent systems and its microscopic mechanisms

Octogen (HMX) is the most powerful military explosive in current use. However, the unclear thermodynamic molecular mechanisms severely limit the development of its production process. In this paper, the solubility of β-HMX in three binary mixed solvent systems (acetone + ethanol, acetone + dichloromethane, acetone + toluene) was measured via a dynamic method at temperature ranging from 283.15 to 313.15 K under atmospheric pressure. The experimental results reveal that the solubility of β-HMX in these binary mixed solvent systems is positively correlated with acetone molar fraction and temperature, and the solvent composition has a greater impact on its solubility compared with the temperature. Moreover, the solubility of β-HMX is further correlated with the Van’t Hoff equation, modified Apelblat equation, CNIBS/R-K model, Jouyban-Acree-Van’t Hoff model, Jouyban-Acree-Apelblat model and NRTL model, and the modified Apelblat equation can give better fitting result (ARD = 8.101 × 10−3, RMSD = 1.065 × 10−5). Finally, the microscopic mechanism of the thermodynamic properties of β-HMX in binary mixed solvents is revealed by investigating the types, intensity and interaction sites of interactions based on density functional theory (DFT) and molecular dynamic (MD) simulation. The results demonstrate that both acetone molecules and ethanol molecules can form certain intermolecular interactions with β-HMX molecules, which are the main driving force of solubilization. In contrast, solvent–solvent interactions have an antagonistic effect on the solubility of β-HMX in mixed solvents. This work can further be informative for researchers in the field of energetic material for the solubility evaluations and provide a reference for the industrial production and performance enhancement of HMX in the future.

Solubility of glibenclamide in carbitol and 1-propanol mixtures at different temperatures

ABSTRACT In this work, the solubility of glibenclamide in the non-aqueous mixtures of carbitol and 1-propanol was studied at temperatures ranging from 293.2 K to 313.2 K using a shake-flask technique. The findings were represented by five computational models, including the van’t Hoff, the Jouyban-Acree, the Jouyban-Acree-van’t Hoff, the mixture response surface and the modified Wilson models. These models showed strong correlation and prediction capabilities, as indicated by the mean relative deviations for the back-calculated data. Furthermore, the thermodynamic analysis was conducted for solubility data using van’t Hoff and Gibbs equations.