Computational studies of gases adsorbed on graphene-like materials
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Nanoporous activated carbons generate interest for their gas storage and separation potential. Generally, adsorbents are assumed rigid, even though they are formed by feeble quasi-2D flakes of graphene. In 2019, Schaeperkoetter et al.^1 observed swelling of graphene oxide frameworks (GOFs) upon supercritical adsorption of various gases. We performed molecular dynamics (MD) simulations of methane and xenon in various models of GOF's with interaction parameters derived from ab initio Density Functional Theory. We observe a monotonic increase of the interlayer spacing consistent with experiments only for a model of benzene-1,4-diboronic acid (DBA) molecules bonded covalently to graphene on both sides of the pore at random orientations, establishing the structure of the DBA-GOFs. Adsorbents are also useful for the separation of gases, e.g., methane and carbon dioxide from organic waste biogas. We performed MD and grand canonical Monte Carlo simulations of the coadsorption of CH4 and CO2 in pores of different sizes and surface functionalization. We observe significant selectivity for the adsorption of CO2 - potentiated by the presence of polar surface groups and determined optimal conditions for gas separation in this system. Finally, atomically flat graphene allows the emergence of two-dimensional films of weakly adsorbed helium with interesting quantum properties. We performed ab initio 2nd order Moller-Plesset calculations with large basis sets of the interaction of 1, 2, and 3 He atoms on graphene-like systems. The interaction parameters are then used in the Bose-Hubbard model, and under certain conditions it is predicted that superfluid or Mott insulating phases can occur.
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Ph. D.