The solution of 6FDA monomer was prepared by dissolving the as-delivered monomer powder (TFC, Japan) in toluene to obtain a concentration of 0.004 g/ml and stirred for 3 hours at room temperature. The base solution is then further diluted with toluene to reach the target concentration.

The triple-layer porous graphene on Si/SiNx chip was mounted onto a lid of a cylindrical container with a 1 cm by 1 cm opening using Kapton tape. Liquid EDA (99%; Sigma-Aldrich) was injected into a crucible located in the container. The liquid EDA was vaporized at room temperature and condensed on the container wall, leading to saturated vapor condition. The vapor can escape through Si/SiNx trenches and, consequently, through nanopores of graphene because of the concentration difference between two sides of the PG membrane. EDA vapors may condense on both top and bottom sides of the graphene. pH paper was mounted on top of the graphene with no direct contact to the surface so that pH paper color change indicates passage of EDA vapor through PG. After an exposure of graphene pores to the saturated EDA for 2 hours, 1 μl of the 6FDA solution was added three times onto the surface of the PG membrane within a 3-min interval using a metallic capillary tube. The solution wetted both sides of graphene, and polyamide formation reaction occurred between 6FDA and EDA at the surface of graphene. Simultaneous to solution addition, a pressure-release lid was opened to avoid overpressurization of the forming nanofilm by the accumulated EDA vapor in the container.

The PG membrane was left exposed to EDA vapor for 20 min to complete the polycondensation reaction following a previously reported reaction time scale of interfacially synthesized polyamide, which lies in the range of 1 to 10 min (36). Subsequently, nonreacted 6FDA was removed by toluene washing. The formed polyamide was then dried, cured, and imidized under N2 atmosphere at 190°C over 2 days. The heating and cooling rates were set to 0.5°C/min.

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