Understanding Gas Transport through Nanopores in Graphene Membranes

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Industrial processes that separate chemical mixtures are essential for civilization, including, for example, the production of energy, materials, and commodity chemicals. The development of more selective and energy efficient separation processes is therefore an important technological challenge, promising the potential for substantial cost savings as well as reductions in energy consumption and harmful emissions. Most industrial separations are energy-intensive thermal processes, which account for 10-15% of the world's overall energy consumption. Membrane-based separation processes offer attractive alternatives to thermal separation techniques due to their reduced energy consumption and excellent reliability. However, the trade-off between gas flux and selectivity of conventional gas separation membranes has historically limited the overall performance of a membrane separation unit, as well as the motivation for replacing energy-intensive processes with these more efficient alternatives. Graphene, an atomically thin layer of carbon atoms, is regarded as the potential ultimate limit of membrane efficiency for gas separation. Graphene and other two-dimensional materials are a single atom or unit cell thick and represent the absolute lowest mass transfer resistance (or highest throughput) among candidate membrane materials. Hence, this ultimate thinness can yield orders of magnitude higher gas fluxes than those attained using conventional membrane materials. To fulfill this potential, the goal of this project is to experimentally generate nanopores in the graphene layer with controlled size distributions for gas separation. Measurements of gas permeation will be used to gain fundamental understanding about molecular transport through these new types of nanopores using a theoretical and simulation framework. The project will contribute to ongoing educational efforts on the MIT campus, including learning modules for a course called Engineering Nanotechnology, and will engage under-represented student populations at MIT and the Cambridge academic community through high school internship and undergraduate research opportunities. The overarching goal of this proposal is to use a combined approach of experiment, molecular simulation, and theoretical analysis to advance the understanding of transport of gas molecules through molecularly sized nanopores in two-dimensional membranes such as graphene. Firstly, theory and simulations will be used to investigate nanopore formation in graphene and to study the permeation kinetics for different gas species through these nanopores, eventually creating a comprehensive theory to predict gas permeation through a realistic pore size distribution. Secondly, nanoporous graphene membranes will be fabricated, and the gas permeances through these membranes will be measured. Lastly, the formation, modification, and functionalization of the graphene pores will be investigated to further understand gas transport through different graphene pore structures. The combination of theory, molecular simulation, membrane fabrication, characterization, and gas flux measurements will provide the first fundamental links between pore structure and distribution with observed gas permeance, and elucidate the underlying mechanisms of molecular-pore interactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.