Storage and separation of gases is one of the most challenging processes when they have to be implemented at industrial scale. Hundreds of potential materials have been tested over the past years, especially for gas storage (hydrogen and methane for fueling applications) and separation of biogas (a mixture of 55 – 75% of methane 25 – 45% of carbon dioxide). Today, MOFs (Metal-Organic Frameworks) [1-2] are considered as the most promising materials for such applications. MOFs are hybrid, nanoporous materials with a very large surface area, in which pore sizes, shapes and adsorption energies can be almost unlimitedly tailored to fit the required adsorption characteristics. A particular category of these materials are the so-called breathing MOFs, in which a reversible structural transformation (variation of pore volume, pore breathing) can be induced by temperature, pressure or interaction with adsorbate molecules. Molecular modeling is an effective way to rapidly obtain microscopic information on the mechanism of adsorption in these materials (in many cases, not accessible using traditional experimental methods) and to shorten the time necessary to implement research results in an industrial process.In the this work we will present simulations of methane and carbon dioxide adsorption in a wide range of MOF structures from CoRE-MOF database [3], and at variable content of humidity. MOFs with pore limiting diffusion (PLD) over 3.3 Å were chosen for the simulations. Due to the humid conditions we chose structures from the middle range of hydrophilicity, kH between 5·10-2 mol/kg·Pa (CuBTC) and 5·10-6 mol/kg·Pa (ZIF-8). Over 1000 structures have been tested using Grand Canonical Monte Carlo method (as implemented in RASPA code) to find the optimal material for the CH4/CO2 separation in conditions of increasing humidity. The initial screening allowed us to select the most promising structures for more detailed investigation. We show that 16 materials exhibit very promising selectivity (defined as adsorbed amount of CO2¬ to amount of CH4) in range from 50 to 440. Furthermore, adsorption of methane tends to be reduced with increasing humidity. Reference[1]S. Li, Y. G. Chung, and R. Q. Snurr, “High-Throughput Screening of Metal–Organic Frameworks for CO 2 Capture in the Presence of Water,” Langmuir, vol. 32, no. 40, pp. 10368–10376, 2016.[2]R. Krishna, “Screening metal–organic frameworks for mixture separations in fixed-bed adsorbers using a combined selectivity/capacity metric,” RSC Adv., vol. 7, no. 57, pp. 35724–35737, 2017.[3]Y. G. Chung et al., “Computation-Ready, Experimental Metal–Organic Frameworks: A Tool To Enable High-Throughput Screening of Nanoporous Crystals,” Chem. Mater., vol. 26, no. 21, pp. 6185–6192, Nov. 2014.

Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form.Here we focus on the influence of confinement on properties of fluids, when the confining volumes are of nanometric size.Using Grand Canonical Monte Carlo simulations we show that when a fluid is confined in nano-volume, delimited by non-attracting pore walls,its density is heterogeneous close to the pore wall, and, on average over the whole pore volume, it is smaller than the density of bulk fluid. Thisfluid heterogeneity, resulting from the nano-confinement, progressively weakens when the pore size increases, and totally disappears inside thepores larger than 5 nm. On the other side, in the limit of very small pores, the fluid density approaches the ideal gas value. This effect should bedistinguished from the well know heterogeneity of density of fluids adsorbed in nanopores, driven by the difference between the strength offluid-fluid and fluid-pore wall interactions, that varies with the distance from the pore wall.We show that the density distribution inside the non-attracting reservoir strongly depends the distance from the pore walls, and the pore size andshape. Such a behavior, although non-intuitive in macroscopic sample, has a simple physical explanation. The energy of a given gas moleculestrongly depends on the number of its nearest neighbors. In the nanopores this number decreases when the molecule is closer to the pore wall.Less intuitive is the observation that at higher pressures (p > 100 bar) the density of the gas close to the wall may be higher than in the middle ofthe pore, and even higher than the one of the bulk gas at the same thermodynamic conditions.

Hydrogen is considered to be the preferred successor to gasoline due to its clean combustion.However, efficient and save storage of hydrogen remains the bottle-neck and one of the main challenges in hydrogen-basedtechnologies. In the past we have justified [1] the necessary conditions (materials physical properties) the hydrogenadsorbents MUST simultaneously fulfilled to be used in mobile applications: it must exhibit the specific surface at least ofthe order of 5000–7000 m2/g, have the average binding energy above 10 kJ/mol, and the density above 0.6 kg/m3. This setof parameters put so strict constrains on possible solutions that such systems are neither yet known nor seem easy tosynthesize.Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

Here we explored the possibility to prepare boron-substituted nanoporous carbons, cheap, light and save material that wassupposed [2,3] to reversibly store hydrogen by physisorption at room temperatures and moderated pressure (< 120 bar). Weshowed that electric arc discharge between graphite electrodes may be optimized to produce graphitized structures with avariety of graphene fragment sizes, forms, and interconnections between them. It also allows to introduce boron heteroatominto graphite-like structure. The as-synthetized material shows the hydrogen binding energy twice as high as unsubstitutedcarbons, but requires post-treatment (activation) as the its surface is low (~200 m2/g).

Phonons are quantum elastic excitations ofcrystalline solids. Classically, they correspond to thecollective vibrations of atoms in ordered periodic structures.They determine the thermodynamic properties ofsolids and their stability in the case of structural transformations.Here we review for the first time the existingexamples of the phonon analysis of adsorption-inducedtransformations occurring in microporous crystallinematerials. We discuss the role of phonons in determiningthe mechanism of the deformations. We point outthat phonon-based methodology may be used as a predictivetool in characterization of flexible microporousstructures; therefore, relevant numerical tools must bedeveloped.

This work investigates the effects of neutron irradiation on nitrogen and hydrogen adsorption in boron-doped activated carbon. Boron-neutron capture generates an energetic lithium nucleus, helium nucleus, and gamma photons, which can alter the surface and structure of pores in activated carbon. The defects introduced by fission tracks are modeled assuming the slit-shaped pores geometry. Sub-critical nitrogen adsorption shows that nitrogen molecules cannot probe the defects created by fission tracks. Hydrogen adsorption isotherms of irradiated samples indicate higher binding energies compared to their non-irradiated parent samples.

Adsorption studies in flexible metal–organic frameworks are challenging and time-consuming. It ismainly because the mechanism of adsorption, defined by structural framework properties, is constantlymodified during the process, as the framework transformation depends on the adsorption uptake. Wepropose here a new approach to investigate adsorption in such complex systems, in which thesimulations of adsorption in a deforming framework are replaced by the analysis of adsorption inintermediate rigid structures. As a proof of concept we analyze carbon dioxide, hexane, and methaneadsorption in MIL-53. 19 intermediate structures were generated using geometrical interpolationbetween the open and the closed MOF forms and optimized with quantum DFT calculations. The grandcanonical Monte Carlo method was applied to calculate adsorption isotherms in all intermediatestructures. The comparison with experimental results enabled the identification of the intermediateadsorption states. The analysis of the microscopic configurations of the adsorbed molecules in thesestructures allowed us to propose a new mechanism of adsorbate evolution over the entire process.