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Abstract: The three-point model and molecular simulation are used to understand the enantioselective adsorption of a homologous series of chiral compounds on a common chiral selector that is incorporated on a solid surface. We demonstrate how the enantioselectivity of homologous chiral compounds may go down, go up, remain the same, or even reverse. Conditions that lead to consistent enantioselectivity for homologous chiral compounds are also proposed. [Copyright &y& Elsevier]

Abstract: Metal-organic frameworks are promising materials for the capture of carbon dioxide. Finding the best metal-organic frameworks from the vast number of possibilities could be greatly accelerated by efficient computational screening techniques. We have previously reported an effective screening protocol for predicting carbon dioxide adsorption performance in metal-organic frameworks that uses grand canonical Monte Carlo simulations of gas adsorption. In the model, molecules interact via van der Waals and electrostatic interactions with each other and the framework. However, the method requires single-point quantum mechanics calculations for the estimation of atomic partial charges. In this study we investigate the feasibility of a modified protocol that bypasses the computationally expensive quantum mechanics calculations by applying instead the charge equilibration method. We compare the results of both protocols directly on fourteen metal-organic frameworks and conclude that the new protocol is sufficiently accurate for screening purposes and is significantly faster. [Copyright &y& Elsevier]

Abstract: Hydrogen adsorption isotherms in 20 metal–organic frameworks (MOFs) were obtained from grand canonical Monte Carlo simulations and used to develop quantitative correlations to quickly estimate the H2 uptake of MOFs at 120bar from the free volume of the adsorbent. These correlations were then verified with a diverse set of 22 MOFs that were not used in developing the correlations. The simulated high-pressure H2 isotherms in five representative MOFs show that extremely high pressures (∼80,000bar) are required to completely fill the MOF pores with H2 at 298K. Nevertheless, much lower pressures (several 100bar) are sufficient to attain the H2 storage targets for MOFs with large free volumes. For IRMOF-16 with a large free volume (4.322cm3/g), only modest pressures (170 and 280bar) are required to achieve the 2010 and 2015 gravimetric targets. However, considerably higher pressures are required for attaining the volumetric targets. In addition, three interesting pressure regions, which are observed in the H2 densities within the MOFs (ρad ) up to very high pressures, are analyzed by radial distribution functions between the adsorbed H2 molecules as well as those between H2 molecules and metal corners. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen storage and delivery in eight representative metal–organic frameworks (MOFs) was investigated using grand canonical Monte Carlo (GCMC) simulations. The simulations demonstrate that the optimal isosteric heat of adsorption (Q st) for maximum hydrogen delivery using MOFs is approximately 20kJ/mol. The results also suggest that increasing the Q st for MOFs with large surface areas (>4800m2/g) is required to attain current hydrogen storage targets in terms of deliverable capacity. [Copyright &y& Elsevier]

Abstract: Molecular simulations were used to screen a diverse collection of eight homochiral metal–organic frameworks (MOFs) for their ability to separate 19 chiral compounds by enantioselective adsorption. The simulation model was validated by comparison with available experimental data. It was found that high enantioselectivity is strongly correlated with a close match between the size of the pore and the size of the chiral sorbate molecule. However, there is also a possibility of no enantioselectivity even when the size of the pore matches with the size of the chiral sorbate molecule. A four-point model was used to explain this observation, and a solution to promote high enantioselectivity has been proposed. [Copyright &y& Elsevier]

Knudsen dynamics simulations were performed in cylindrical pores with multiple sections of different diameters. The number and location of hits between particles and the pore walls can be related to the known distributions in the uniform diameter cases. Both sweep-gas and pass-through modes of operation were examined. The contact of the particles traveling inside the pores with the pore walls can be regulated by adjusting the aspect ratio (section length/section diameter) of the pore sections and the ratio of their cross-sectional areas. The results were found to be independent of the transition angle between sections except for very smooth transitions. Analytical expressions were developed to relate the transmission probability in pores of multiple sections to the transmission probabilities of the constituent sections. [Copyright &y& Elsevier]

Abstract: A piston-based particle damper geometry is proposed and investigated using experiments and particle dynamics simulations. In particle damping, energy is dissipated through the inelastic collisions and friction between granular particles. Due to their temperature-independent performance, particle dampers are promising alternatives for use in extreme temperature conditions. Using the appropriate inter-particle force models, the simulations agree well with the experimental results. Using simulations, many parameters are investigated in this work for their effects on the damping performance, including material properties, particle size, device geometry, and excitation level. These results provide new understanding of particle damping and may help in the design of next generation particle dampers. [Copyright &y& Elsevier]