As part of a national research collaboration, Spanish researchers including the ICN2 have reached a milestone in graphene research, that potentially brings science a step closer to using graphene in filtration and sensing applications.

The researchers have successfully synthesized a graphene membrane with pores whose size, shape and density can be tuned with atomic precision at the nanoscale. Engineering pores at the nanoscale in graphene can change its fundamental properties. It becomes permeable or sieve-like, and this change alone, combined with graphene's intrinsic strength and small dimensions, points to its future use as the most resilient, energy-efficient and selective filter for extremely small substances including greenhouse gases, salts and biomolecules.

An additional, perhaps less intuitive change also takes place when the spacing between pores is similarly reduced to a few atoms. Doing so transforms the graphene from semimetal to semiconductor, opening the door for its use in electronic applications, where it could be used to replace the bulkier, more rigid silicon components used today.

However, producing such a material requires a precision that current fabrication methods have yet to achieve.Punching holes or otherwise manipulating a material that a single atom thick is an incredibly hard task. In the work described here, the team takes a "bottom up" approach based on the principles of molecular self-assembly and 2-D polymerization, effectively growing the graphene from scratch with the nanopores already built-in.

For this approach to succeed, the researchers need a very specific precursor molecule to use as initial building blocks that would behave as intended when subjected to different stimuli. In this work, these precursors were designed and produced by synthetic chemistry specialists at CiQUS, before being taken to the ICN2 for the "bottom-up" assembly of nanoporous graphene.

They were subjected to several rounds of heating at high temperatures while placed on a gold surface, which serves to catalyze the reactions by which the molecules are first polymerized, to form long, lace-like nanoribbons, and then bonded laterally, to create the desired 2-D nanomesh structure complete with evenly spaced, evenly sized pores.



Simulated at the DIPC and tested experimentally at the ICN2, the result is a new kind of graphene that exhibits electrical properties similar to those of silicon, and can also act as a highly selective molecular sieve. Applied in conjunction, these two properties are predicted to allow the development of combined filter and sensor devices, which will not only sort for specific molecules, but will alternatively block or monitor their passage though the nanopores using an electric field. Such electrical readings would provide additional information as to precisely what concentrations of which molecule are passing through the pores and when, something which also points to possible applications in more efficient DNA sequencing.

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