Structure, Dynamics, and Thermodynamics of Intruded Electrolytes in ZIF-8

Abstract

We report here the properties of LiCl aqueous solutions at various concentrations confined inside the pores of the ZIF-8 metal-organic framework, based on classical molecular dynamics simulations. This system has been proposed for applications in the storage or dissipation of mechanical energy, using the liquid-phase intrusion of concentrated electrolytes in the hydrophobic framework. We describe the structure of the liquids and the influence of confinement, their dynamics, the mechanical properties of ZIF-8 and the impact of liquid intrusion on them. We show that the presence of the electrolyte has a moderate impact on the ZIF-8 framework, while the presence of the ZIF-8 matrix strongly influences the behavior of the confined aqueous solution, affecting the overall properties of the system. We also computed the free energy profile for the entry of water molecules and ions into the nanopores, showing a difference between anions and cations.

Structure and dynamics of a water/methanol mixture confined in zeolitic imidazolate framework ZIF-8 from atomistic simulations

“…The swing angle distribution for the empty ZIF-8 framework is close to a Gaussian distribution, centered near 12° and with fluctuations of the order of 10°, which is in good agreement with previous studies. 63 With increasing loading of the water/methanol mixture, a small gradual decrease of the most probable swing angle can be observed, although the fluctuations still have the same order of magnitude. This behavior is in contrast to the adsorption of nitrogen in ZIF-8, 49 where the maximum value shifts from 0° to 25° as the pores are filled up with nitrogen using first-principles MD simulations.…”

The Formation and Decay of an Unstable State of a Suspension of Hydrophobic Nanoporous Particles under Rapid Compression

“…The porous material L23 is KSK-G silica gel with the SiO 2 skeleton material, the surface of which was chemically modified with alkylsilanes, to produce hydrophobic properties to the pore surface [25]. Using the methods of low-temperature nitrogen adsorption [26], helium pycnometry [26], and liquid porometry [17], the following characteristics of porous media were determined and within the limits of the error coincide with the results obtained in [27]: specific pore volume (V por ) (0.56 ± 0.02) cm 3 /g, skeleton density (ρ pm ) (1.7798 ± 0.0016) g/cm 3 , specific surface area (S por ) (212 ± 7) m 2 /g (multipoint BET), specific volume of the porous medium (V pm = 1/ρ pm + V por ) ∼ 1.22 cm 3 /g, granule size (L) ∼ 10 µm, average pore size (< R >) (5.0 ± 0.2) nm, porosity (ϕ) ∼ 0.52 and characteristic of the pore size distribution function (δR/ < R >) ∼ 0.1. In addition, the compressibility of an unfilled porous medium (χ pm ) ∼ 0.41 • 10 −2 MPa −1 , the pressure value of the beginning of filling of pores under the conditions of a slow (quasistatic) pressure change (P c0 ) (15 ± 1) MPa, independent of the velocity of the rod according to [17].…”

“…In the experiment, 5 g of the porous medium L23 was placed in the permeable for the liquid container in a high-pressure chamber with a volume of ∼ 60 cm 3 . The inter-granular space in the container and the remaining volume of the chamber were filled with DW.…”

“…More recently, new directions in the study of transport in the zeolites subnanometer channels, in nanometer pores of disordered media such as silica gels, carbon nanotubes, metal-organic structures have arisen [3][4][5][6][7][8]. To describe molecular transport in nano-subnanostructures, it is necessary to take into account local and long-range correlations of liquid in different pores.…”

“…Repeated use is possible if porous media and liquids are used, which, when impacted, are in an unstable state with filled pores, and the liquid quickly flows out with a decrease in pressure [13]. In the intrusion-extrusion regime close to quasistatic filling, the dependencies of pressures P int and P ext for zeolites [3], for silica gels with a modification to provide hydrophobic properties to the surface of pores and non-wetting liquids-water, aqueous solutions of salts and organic substances, were determined [14][15][16][17]. It was also established that the filling pressure P int for various systems increases with an increase in the transport velocity of non-wetting liquids in porous microparticles [18].…”