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The importance of nitrate and ammonium salts both in the environment and in biological processes cannot be questioned. In this work, using the TIP4P/2005 water model, aqueous solutions of nitrate and ammonium electrolytes are parametrized using scaled charges while keeping a rigid structure and nonpolarizable charge distributions. The models are optimized by systematically testing a set of properties for twelve electrolytes—eight nitrate and four ammonium salts—thus, enlarging the number of potential chemical species encompassed within the Madrid-2019 force field for ions. The capacity of the force field for predicting densities, ion–ion and ion–solvent structures, and transport properties of the solutions comprised by the trial batch of salts was tested and discussed. Both the dependence of the densities with the salt concentration and the solution structure were nicely reproduced by the models in the whole concentration range without any trace of precipitating events and with improved accuracy in comparison with recently reported models, while the agreement of the simulated transport properties with experimental data ranges from good to reasonable, depending on the ion/counterion pair. These scaled charge models might be considered as force fields embodying a reasonable compromise between exactness and general applicability and also as an important step in the development of accurate models for polyatomic ions. [ABSTRACT FROM AUTHOR]

Thermodynamic and transport properties of particles interacting via the triangular-well potential in the range of $ 1.4 \leq \lambda \leq ~2.6 $ 1.4 ≤ λ ≤ 2.6 have been studied using perturbation theory and Molecular Dynamics simulations. We present thermodynamic properties such as vapour-liquid coexistence, vapour pressures, and density for different values of the attractive range potential. Good agreement is observed between the theoretical approach and computer simulations in a wide range of densities, temperatures, and pressures. Additionally, we show Molecular Dynamic simulation results of transport properties such as the self-diffusion coefficient as a function of both density and temperature. Finally, thermodynamic and transport properties of real fluids like oxygen, methane, hydrogen sulfide, and fluoromethane have been predicted using both approaches. Results of vapour-liquid coexistence, vapour pressures, and critical points were in excellent agreement with experimental data. The coupling of perturbation theory, Molecular Dynamics simulations, and the triangular-well pair potential offers a versatile and efficient method to explore various real fluid systems, which would include associating fluids, complex molecular liquids, and colloidal systems. This approach can advance our understanding of these systems using a simple approach and to contribute the development of more accurate and predictive models. [ABSTRACT FROM AUTHOR]

The development of adsorbents for air pollutant remediation and effective monitoring is of interest. Then, the effect of the APTES functionalization ratio on the impact of the adsorption and detection of SO2 molecules was evaluated. The higher APTES functionalization material (SBA-15_6.1APTES) shows a high uptake of 1.15 mmol g−1 at 0.001 bar and 298 K. Fluorescence, time-resolved photoluminescence, and quantum yield experiments revealed a turn-on effect specifically for SO2 molecules, indicating high selectivity, suggesting host-to-guest energy transfer. Attractively, XPS measurement provided an understanding of the mechanism, suggesting hydrogen bonding and dipole–dipole interactions as the main interactions between SO2 molecules and SBA-15_6.1APTES. DFT calculations were performed to confirm these interactions. Furthermore, this study highlights the application of SBA-15 materials with different amino modifications for SO2 treatment and provides insight into the interaction mechanism using experimental techniques. [ABSTRACT FROM AUTHOR]

We have explored adsorption of a single waterlike model in slitlike pores with walls chemically modified by tethered chains that form molecular brushes. Principal focus of the present study is in the evolution of the microscopic structure of fluid species and of a system of chain molecules upon adsorption. A density functional approach is used. Various projections of the vapor–liquid coexistence envelope, including brushes interdigitation coefficient, are obtained and discussed. We have discovered that the molecular brushes can shrink or "swell" upon phase transition in confined water dependent on the attraction between fluid molecules and chains segments. Trends of behavior of the solvation force between pore walls are investigated dependent on the parameters of the system. Particular attention is paid to the appearance of the effective attraction between pore walls. [ABSTRACT FROM AUTHOR]

The density profiles, adsorption isotherms, and phase behavior of a water model in a slit-like pore with walls modified by pre-adsorbed tethered chain molecules have been studied in the framework of a density functional theory. Each chain is bonded to the surface by its terminal segment, and the surface density of grafted chains is the same for each wall. The model for water taken from the work of Clark et al. [Mol. Phys. 104, 3561 (2006)] reproduces successfully a bulk equation of state. The mean field approach has been used to describe the effects of attractive interactions. The chemical association effects are taken into account by using the first-order thermodynamic perturbation theory of Wertheim. We have found that the presence of molecular brushes on the pore walls has important consequences for the adsorption and phase behavior of confined water. If the brush segments do not attract water molecules strongly, the vapor-liquid coexistence envelope shrinks upon increasing brush density, but the critical temperature is weakly affected. Alteration from capillary condensation to evaporation is observed with changes in the brush density, number of segments of tethered chains, and/or chemical identity of segments. The crossover temperature is affected by all these factors. Moreover, we have shown that affinity of water to segments of tethers is an important factor determining adsorption of water vapor and the entire phase diagram. [ABSTRACT FROM AUTHOR]

The adsorption and phase behavior of two model fluids, both with square well inter-particle attraction and site-site associative interaction, in slit-like pores have been studied in the framework of a density functional theory. The mean field approach and the first-order mean spherical approximation have been applied to account for the attractive interactions. The chemical association effects are taken into account by using the first-order thermodynamic perturbation theory of Wertheim. A set of parameters for each fluid model has been chosen according to the work of [Clark et al., Mol. Phys. 104, 3561 (2006)], to describe successfully the vapor-liquid coexistence of water in the bulk phase. The influence of the slit-like pore width and of the strength of gas-solid interaction energy on the vapor-liquid coexistence envelope under confinement has been explored in detail. The theory and the results of the present work are valuable for further exploration of a wide set of models of associating fluids and of fluids with complex molecular architecture in different adsorbents, and to deal with activated carbon surfaces. [ABSTRACT FROM AUTHOR]

The interest in the description of the properties of fluids of restricted dimensionality is growing for theoretical and practical reasons. In this work, we have firstly developed an analytical expression for the Helmholtz free energy of the two-dimensional square-well fluid in the Barker–Henderson framework. This equation of state is based on an approximate analytical radial distribution function for d-dimensional hard-sphere fluids (1 ≤ d ≤ 3) and is validated against existing and new simulation results. The so-obtained equation of state is implemented in a discrete perturbation theory able to account for general potential shapes. The prototypical Lennard-Jones and Yukawa fluids are tested in its two-dimensional version against available and new simulation data with semiquantitative agreement. [ABSTRACT FROM AUTHOR]

The liquid-vapor coexistence (LV) of bulk and confined quantum fluids has been studied by Monte Carlo computer simulation for particles interacting via a semiclassical effective pair potential Veff(r) = VLJ + VQ, where VLJ is the Lennard-Jones 12-6 potential (LJ) and VQ is the first-order Wigner-Kirkwood (WK-1) quantum potential, that depends on β = 1/kT and de Boer's quantumness parameter [formula], where k and h are the Boltzmann's and Planck's constants, respectively, m is the particle's mass, T is the temperature of the system, and σ and [variant_greek_epsilon] are the LJ potential parameters. The non-conformal properties of the system of particles interacting via the effective pair potential Veff(r) are due to Λ, since the LV phase diagram is modified by varying Λ. We found that the WK-1 system gives an accurate description of the LV coexistence for bulk phases of several quantum fluids, obtained by the Gibbs Ensemble Monte Carlo method (GEMC). Confinement effects were introduced using the Canonical Ensemble (NVT) to simulate quantum fluids contained within parallel hard walls separated by a distance Lp, within the range 2σ <= Lp <= 6σ. The critical temperature of the system is reduced by decreasing Lp and increasing Λ, and the liquid-vapor transition is not longer observed for Lp/σ < 2, in contrast to what has been observed for the classical system. [ABSTRACT FROM AUTHOR]

The solvation force of the water-like fluid models with square-well attraction and site–site chemical association confined to slit-like pores has been explored. Theoretical procedure is based on the application of the density functional approach with mean-field approximation for the attractive interparticle interactions. The chemical association effects are treated by using the first-order thermodynamic perturbation theory of Wertheim. Trends of behaviour of the solvation force are put in correspondence with the distribution of molecules in the pores and with the average density of the adsorbate. Moreover, the distribution of non-bonded species on pore width is described. The influence of the width of the square-well and of the gas–solid attraction is discussed. A comparison of theoretical predictions with computer simulations results for water models in slit-like pores is performed. [ABSTRACT FROM AUTHOR]

Thermodynamic properties of quantum fluids are described using an extended version of the statistical associating fluid theory for potentials of variable range (SAFT-VR) that takes into account quantum corrections to the Helmholtz free energy A, based on the Wentzel-Kramers-Brillouin approximation. We present the theoretical background of this approach (SAFT-VRQ), considering two different cases depending on the continuous or discontinuous nature of the particles pair interaction. For the case of continuous potentials, we demonstrate that the standard Wigner-Kirkwood theory for quantum fluids can be derived from the de Broglie-Bohm formalism for quantum mechanics that can be incorporated within the Barker and Henderson perturbation theory for liquids in a straightforward way. When the particles interact via a discontinuous pair potential, the SAFT-VR method can be combined with the perturbation theory developed by Singh and Sinha [J. Chem. Phys. 67, 3645 (1977); and ibid. 68, 562 (1978)]. We present an analytical expression for the first-order quantum perturbation term for a square-well potential, and the theory is applied to model thermodynamic properties of hydrogen, deuterium, neon, and helium-4. Vapor-liquid equilibrium, liquid and vapor densities, isochoric and isobaric heat capacities, Joule-Thomson coefficients and inversion curves are predicted accurately with respect to experimental data. We find that quantum corrections are important for the global behavior of properties of these fluids and not only for the low-temperature regime. Predictions obtained for hydrogen compare very favorably with respect to cubic equations of state. [ABSTRACT FROM AUTHOR]

Abstract The phase behavior of a model fluid with square well inter-particle attraction in slit-like pores has been studied by using a density functional theory. The mean field theory and the first-order mean spherical approximation have been applied to account for the attractive interactions. The influence of the pore width, the gas-solid interaction energy and of the square well width on the phase behavior have been explored in detail. Dependent on the values of parameters of the model, we observed capillary condensation and capillary evaporation, in some cases layering phase transition has been obtained as well. Also, a crossover between condensation and evaporation has been described. The theory and the results obtained in the present work are valuable for future theoretical exploration of water-like and other models under confinement that intrinsically involve square well as a reference ingredient. Graphical abstract Image 1 Highlights • Theoretical description of the phase behavior of square-well fluids in slit-like pores. • Density functional theory has been applied for the description of confined fluid. • Attractive interactions are described using first-order mean spherical approximation. • Layering phase transition, capillary condensation and evaporation has been described. [ABSTRACT FROM AUTHOR]

A liquid-vapor coexistence envelope for water-like models with square-well attraction between particles and with four attractive associating sites per particle has been investigated. The mean-field theory and the first-order mean spherical approximation for attractive interactions together with the first-order thermodynamic perturbation theory of Wertheim for association have been applied to construct the temperature - density and the temperature - chemical potential projections of the equation of state. In addition, the dependence of the fraction of non-bonded particles on the parameters of the models has been evaluated and analyzed. We explored a set of models with different square-well width and energy of associative interaction. In some cases a comparison with computer simulation data has been performed. For two specific parameter sets previously proposed to mimic water properties a comparison with experimental data for the vapor-liquid coexistence envelope and for vapor pressure has been performed. It is shown that the applied theoretical procedures are successful and can be used with confidence. On the other hand, they provide solid basis to apply in the theory of inhomogeneous associating fluids. [ABSTRACT FROM AUTHOR]

Semiclassical versions of the statistical associating fluid theory for three- and two-dimensional chain molecules with attractive potentials of variable range (SAFT-VRQ) are applied to model selectivities and adsorption isotherms of mixtures containing hydrogen (H 2 ) and methane (CH 4 ) onto metal-organic frameworks (MOFs). The theoretical model for mixtures relies on eight molecular parameters and their corresponding combining rules. Six of the eight parameters are obtained from the bulk properties of pure components and only the other two, related to the energy depth of the surface-particle potential, ε w , and the surface area S , are determined from fitting to experimental data of adsorption isotherms of pure components. The obtained S values are in agreement with reported BET surface areas. Satisfactory results are obtained for the prediction of adsorption isotherms for pure substances and mixtures containing hydrogen and methane compared with experimental data. This molecular thermodynamic model is also able to describe adsorption selectivities in mixtures and the relevance of the quantum description as the molar fraction of hydrogen is increased. Finally, we include detailed information about all the mathematical expressions used to describe the adsorption isotherms of mixtures. [ABSTRACT FROM AUTHOR]

In this work the statistical associating fluid theory for chain molecules with attractive potentials of variable range (SAFT-VR) and its two-dimensional version (SAFT-VR-2D) are applied to model thermodynamic properties of adsorption of water and methanol onto several types of adsorbents: activated carbons, metal organic frameworks (MOF) and carbon molecular sieve membranes. Fluid molecules are hard-spheres particles with square-well (SW) attractive interactions used to model particle-particle and particle-surface interactions. Associating interactions are described with two, three and four SW sites. Satisfactory results are obtained when compared with experimental data within a wide range of temperatures and pressures, including the reproduction of adsorption isotherms type V in the case of water. We include predictions for the relationship between mole fractions for adsorbed and bulk molecules, and how these properties are modified by the presence of association in both phases. [ABSTRACT FROM AUTHOR]

In this work, a molecular simulation study of confined hard-spheres particles with square-well (SW) attractive interactions with two and four associating SW sites based on the first-order perturbation form of Wertheim’s theory is presented. An extended version of the Gibbs ensemble technique for inhomogeneous fluids [A. Z. Panagiotopoulos, Mol. Phys. 62, 701 (1987)] is used to predict the adsorption density profiles for associating fluids confined between opposite parallel walls. The fluid is confined in four kinds of walls: hard-wall, SW wall, Lennard-Jones (LJ) 12-6 wall potential, and LJ 10-4 wall potential. We analyze the behavior of the confined system for several supercritical temperatures as a function of variation of molecular parameters: potential range λ, bulk densities ρ b * , pore width H, cutoff range interaction r c * , and range of the potential and depth of the particle-wall ( λ w , ε w * ). Additionally, we include predictions for liquid-vapor coexistence of bulk associative particles and how their critical properties are modified by the presence of associative sites in the molecule. The molecular simulation data presented in this work are of prime importance to the development of theoretical approaches for inhomogeneous fluids as classical density functional theory. The simulation results presented here are resourceful for predicting adsorption isotherms of real associating fluids such as water. [ABSTRACT FROM AUTHOR]

Adsorption of molecular hydrogen () onto graphene and other carbon-based substrates is currently a research area of interest, where molecular-based approaches are required to describe thermodynamic properties of this and other related systems. We present a semiclassical theoretical framework to model adsorption isotherms of quantum fluids such as, based on the statistical associating fluid theory for chain molecules interacting with potentials of variable range for classical and quantum bulk fluids (SAFT-VRQ), and its extension to describe adsorbed systems (SAFT-VR-2D). Although the application of the theory relies on the determination of eight molecular parameters, seven of them can be obtained from bulk thermodynamic properties, the ratio of the critical temperatures of the adsorbed and bulk phases, and theoretical estimations about the range of the surface-particles potential and the energy depth of the particle–particle potential of the adsorbed fluid. The energy depth of the surface-particle potential, εw, is the free molecular parameter that can be obtained by fitting to experimental data of adsorption isotherms. Results obtained for εwaccording to this procedure are consistent with experimental values of the isosteric heat and the prediction of adsorption isotherms is in very good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: A thermodynamic consistency of isothermal vapor–liquid equilibrium data for 9 non-polar and 8 polar binary asymmetric mixtures at high pressures has been evaluated. A method based on the isothermal Gibbs–Duhem equation was used for the test of thermodynamic consistency using a Φ–Φ approach. The Peng–Robinson equation of state coupled with the Wong–Sandler mixing rules were used for modeling the vapor–liquid equilibrium (VLE) within the thermodynamic consistency test. The VLE parameters calculations for asymmetric mixtures at high pressures were highly dependent on bubble pressure calculation, making more convenient to eliminate the data points yielding the highest deviations in pressure. However the results of the thermodynamic consistencies test of experimental data for many cases were found not fully consistent. As a result, the strategies for solving these problems were discussed in detailed. [Copyright &y& Elsevier]

Abstract: In the present work, the estimation of the parameters for asymmetric binary mixtures of carbon dioxide+ n-alkanols has been developed. The binary interaction parameter k 12 of the second virial coefficient and non-random two liquid model parameters τ 12 and τ 21 were obtained using Peng–Robinson equation of state coupled with the Wong–Sandler mixing rules. In all cases, Levenberg–Marquardt minimization algorithm was used for the parameters optimization employing an objective function based on the calculation of the distribution coefficients for each component. Vapor–liquid equilibrium for binary asymmetric mixtures (CO2 + n-alkanol, from methanol to 1-decanol) was calculated using the obtained values of the mentioned parameters. The agreement between calculated and experimental values was satisfactory. [Copyright &y& Elsevier]

The archetypical metal-organic framework (MOF), HKUST-1, has been systematically modified in both its organic and inorganic building blocks to introduce diversity in the metal centers and create defects within the network, achieving a variety of bimetallic hierarchical structures. These modifications changed the affinity of the MOFs for acid gases. The introduction of bimetallic sites mostly affects CO 2 adsorption, while the hierarchical structure generates an increase in SO 2 uptake capacity, allowing better performance in the separation of binary mixtures of these gases near room temperature. Notably, the synthesized HH-Cu 100 material exhibited an exceptionally high IAST SO 2 /CO 2 (10:90) selectivity of 3420 at 298 K, outperforming benchmark MOFs with open metal sites.

The development of adsorbents for air pollutant remediation and effective monitoring is of interest. Then, the effect of the APTES functionalization ratio on the impact of the adsorption and detection of SO 2 molecules was evaluated. The higher APTES functionalization material (SBA-15&#95;6.1APTES) shows a high uptake of 1.15 mmol g -1 at 0.001 bar and 298 K. Fluorescence, time-resolved photoluminescence, and quantum yield experiments revealed a turn-on effect specifically for SO 2 molecules, indicating high selectivity, suggesting host-to-guest energy transfer. Attractively, XPS measurement provided an understanding of the mechanism, suggesting hydrogen bonding and dipole-dipole interactions as the main interactions between SO 2 molecules and SBA-15&#95;6.1APTES. DFT calculations were performed to confirm these interactions. Furthermore, this study highlights the application of SBA-15 materials with different amino modifications for SO 2 treatment and provides insight into the interaction mechanism using experimental techniques.