Permeation Mechanisms Through 1 nm Thin Carbon Nanomembranes

Molecular thin carbon nanomembranes (CNMs) synthesized by electron irradiation induced cross-linking of aromatic self-assembled monolayers (SAMs) are promising 2D materials for the next generation of filtration technologies [1, 2]. Their unique properties including ultimately low thickness of ~1 nm, sub-nanometer porosity, mechanical and chemical stability are attractive for the development of innovative filters with low energy consumption, improved selectivity and robustness. However, the permeation mechanisms through CNMs resulting in, <i>e.g.</i>, an ~1000 times higher fluxes of water in comparison to helium have not been yet understood [1]. Here we report a study of the permeation of He, Ne, D₂, CO₂, Ar, O₂ and D₂O using mass spectrometry in the temperature range from room temperature to ~120 °C. As a model system, we investigate CNMs made from [1'',4',1',1]-terphenyl-4-thiol SAMs. We found out that all studied gases experience an activation energy barrier upon the permeation which scales with their kinetic diameters. Moreover, their permeation rates are dependent on the adsorption enthalpy on the nanomembrane surface. These findings enable us to rationalize the permeation mechanisms and establish a model, which paves the way towards the rational design not only of CNMs but also of other organic and inorganic 2D materials for energy-efficient and highly selective filtration applications [3].<br/><br/>[1] Y. Yang <i>et al.</i>, <i>ACS Nano</i> <b>2018</b>, 12, 4695<br/>[2] Y. Yang <i>et al.</i>, <i>Adv. Mater.</i> <b>2020</b>, 32, 1907850<br/>[3] V. Stroganov <i>et al</i>, <i>Small </i><b>2023</b>, https://doi.org/10.1002/smll.202300282