The greater structural versatility of two-dimensional polymeric nanosheets could be available through the development of a bottom-up polymerization strategy compared with top-down nanosheets (such as graphene and metal chalcogenides). However, rational synthesis by solution polymerization has been a long-standing challenge. Considering that Glaser coupling is catalyzed by cuprous (I) salts with the participation of oxygen, an air/liquid interfacial coupling reaction has been designed and used to prepare a two-dimensional porous triptycene-based polymeric nanosheet (2D-PTNS). This 2D-PTNS shows a high BET surface area, good gas adsorption ability and excellent selective adsorption of C₂H₆/CH₄ at ambient temperature and pressure.