Computational Studies of Quantum Gas Transmission Through Nanoporous Graphene Membranes

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Title: Computational Studies of Quantum Gas Transmission Through Nanoporous Graphene Membranes
Author: Brockway, Anna M.
Advisor: Schrier, Joshua
Department: Haverford College. Dept. of Chemistry
Type: Thesis (B.S.)
Issue Date: 2012
Abstract: Clean and efficient gas separation is a longstanding challenge which, if met, could provide the means to reduce the concentration of atmospheric greenhouse gases and supply pure gas and isotope samples to industry, medicine, and research. Conventional methods for gas separation are cumbersome and energy-intensive, while newer membrane- and polymer-driven processes are specifically tailored to particular systems and often suffer from low selectivity. A systematic approach is necessary to productively account for the diversity of situations where gas separation is needed. This study addresses the viability of porous graphene derivatives and graphene allotropes as selective filters for noble gases, which are chosen here as a model system. A diverse array of possible structures for molecular membranes derived from porous graphene is proposed, and plane-wave pseudopotential density functional theory (DFT) calculations are used to determine the potential energy surfaces for the transmission of noble gas atoms through these structures. The finitedifference method is used to calculate the tunneling probabilities of noble gas atoms through the porous graphene structure, giving information about the quantum mechanical behavior of the particles that is crucial to isotope separation. Empirical van der Waals dispersion corrections are applied, and potential energy surfaces are analyzed to yield greater insight about the model system. Notably, attractive interactions lead to potential wells in energy barriers which scale with increasing pore size. Parameters conducive to favorable gas transmission, including structure stability, atom type and size, partial charge distributions, and van der Waals radius overlap, are evaluated to predict the behavior of the structures in real-world systems. Pair potential models such as 12-6 and 9-6 Lennard-Jones, Buckingham, and Born-Mayer-Huggins are evaluated for their ability to describe DFT calculations. Finally, the feasibility of a double-barrier porous graphene system held together by interactions with lithium atoms is investigated, and resonant tunneling through the system is observed. These findings yield a number of computational and structural insights key to the further development of systematic processes for gas separation through molecular membranes. Computational insights regarding the size of the investigated systems, required plane-wave cutoffs, necessity of dispersion corrections, and feasibility of fitted pair-potential models allow for simplified calculations in future studies. Structural insights include specific stability requirements for systems derived from porous graphene, correlations to partial charge distributions, and the effect of relative van der Waals overlap within gas separation systems. All of these aid the future systematic development of filtration membranes derived from porous graphene.
Subject: Gas separation membranes
Subject: Graphene
Subject: Nanopores
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Brockway, Anna M.. "Computational Studies of Quantum Gas Transmission Through Nanoporous Graphene Membranes". 2012. Available electronically from

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