Tailored Permeation Through ≈1 nm Thick Carbon Nanomembranes by Subtle Changes in Their Molecular Design

Abstract Due to their nanoscale thickness (≈1 nm) and exceptional selectivity for permeation of gases, nanomembranes made of 2D materials possess high potential for energy‐efficient nanofiltration applications. In this respect, organic carbon nanomembranes (CNMs), synthesized via electron irradiation‐induced crosslinking of aromatic self‐assembled monolayers (SAMs), are particularly attractive, as their structure can be flexibly tuned by choice of molecular precursors. However, tailored permeation of CNMs, defined by their molecular design, has not been yet demonstrated. In this work, it is shown that the permeation of helium (He), deuterium (D₂) and heavy water (D₂O) for CNMs synthesized from biphenyl‐based SAMs on silver (C₆H₅‐C₆H₄‐(CH₂)_n‐COO/Ag, n = 2–6) can be tuned by orders of magnitude by changing the structure of the molecular precursors by just a single methylene unit. The selectivity in permeation of D₂O/D₂ with an unprecedented value of 200 000 can be achieved in this way. The temperature‐dependent study reveals a clear correlation between the molecular design and the permeation mechanisms facilitating therewith tailored synthesis of molecular 2D materials for separation technologies.