When more than 2 g of alumina was used, the template could not be fully removed. In this case, the chemical etching process with HF was repeated. The carbon on the filter was then washed with water 5 times. After the filtration, the wet sample was immersed in an organic solvent (acetone or isopropyl alcohol), and the mixture was stirred at 323 K (50 ºC) for 6 h in total. Water was substituted with organic solvents to prevent the graphene architecture from shrinking under the intense capillary force of water. The solvents were then filtered off on a hydrophilic PTFE membrane, and the obtained carbon was dried under vacuum at 373 K (100 ºC) overnight to give the nanoporous carbon materials (NPCs). The average number of graphene walls ngra was calculated to be ~1.1 by the TG analysis using an equation mentioned in the Table . NPCs were then annealed at 2073 K (1800 ºC) in an induction heating furnace or tabletop high temperature electric furnace for 0.5-1 h under a steady flow of Ar to afford the nanoporous graphene materials (NPGs).