(507d) Mechanistic Insights Based Synthesis and Scale-up of Atom-Thin CO2-Selective Porous Graphene Membranes

Porous two-dimensional (2D) selective films where pores act as zero-dimensional aperture are highly attractive for rapid permeation of molecules where one can tune molecular transport, and therefore, molecular selectivity and flux by tuning pore size and pore edge functional groups. Porous single-layer graphene film has emerged as a highly attractive candidate to achieve ultrahigh flux given that it is just one atom thick, and that the scale-up of large area graphene by chemical vapor deposition is already successful. However, pore formation for selective CO2 removal as well as scalable fabrication of graphene membranes remains a challenge.

Controlled oxidative etching of graphene, e.g., using ozone, is highly attractive because one can decouple the events that leads to pore nucleation and growth. This allows one to control pore size by systematic oxidant exposure. A series of events takes place during oxidation ultimately yield a Å-scale pore. Briefly, this involves a cooperative assembly of epoxies which first forms cyclic epoxy trimers followed by linear chains of trimers, and finally an ordered honeycomb superstructure. The degree of order in these clusters is highly surprising mainly because oxidized graphene domains were once thought to be amorphous. Luckily, it opens new avenues to control the pore size, e.g., by a controlled gasification of the cluster. The knowledge of edge functional group surrounding graphene pore, previously inaccessible by the microscopy studies, allows one to also carry out controlled functionalization of pore, e.g., to incorporate pyridinic N at the pore which remarkably improve the CO₂/N₂ separation performance of the pore. Thanks to the simplified chemistry of forming pores, and recent progress in crack-free transfer of graphene, A4-sheet-sized membranes could be prepared. Field trial of these membranes in a carbon capture pilot & demonstration project show highly promising results including stability in flue gas containing 50 ppm of NO_x and SO_x. Based on this results, a roll-to-roll fabrication tool for graphene membrane is being fabricated to demonstrate fabrication of 40 m² area graphene membrane to allow capture at the rate of 1 ton_CO2/day by the year 2027.

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