Carbon Nanomembranes with Sub-Nanometer Channels: Two-Dimensional Materials for Water Purification with High Selectivity and Permeance

Clean water is a global challenge, and membrane filtration is a key technology to achieve it. We report on the fabrication, characterization and application of terphenylthiol carbon nanomembrane (TPT-CNM), a 2D-material perforated by sub-nanometer channels. We show that free-standing TPT-CNMs are excellent water filters, combining a high selectivity with an exceptionally high water permeance.

TPT-CNMs are fabricated from terphenylthiol molecules by a well-established procedure [1] of (i) self-assembled monolayer formation on a gold surface, (ii) electron radiation induced cross-linking, and (iii) a lift-off of the 2D network of cross-linked molecules. This results in the creation of a ~1.2 nm thick carbon nanomembrane that is perforated by a network of sub-nanometer channels. The channels can be clearly seen by tapping mode atomic force microscopy and AFM image analysis yields average channel diameters below ~0.7 nm and areal channel densities of ~10¹⁸ m⁻² [2].

We tested TPT-CNMs as molecular filter membranes and found that they efficiently block the passage of most gases and liquids. However, water passes through, and it does this with an exceptionally high permeance of ~1.1×10⁻⁴ mol·m⁻²·s⁻¹·Pa⁻¹. This suggests that water molecules translocate fast and cooperatively through the sub-nanometer channels. Assuming all channels in a TPT-CNMs are active in mass transport, we find a single-channel permeation of ~66 water molecules·s⁻¹·Pa⁻¹. We will compare this with molecular transport through other carbon nanoconduits, such as carbon nanotubes or membrane proteins (aquaporins) [3,4,5]. As the fabrication of TPT-CNMs is scalable, their utilization opens a new path towards the application of 2D-materials in water purification.

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