Single-crystal 2D covalent organic frameworks for high-capacity methane storage

2D covalent organic frameworks (COFs) usually possess a polycrystalline nature as well as lower porosity and surface area than 3D counterparts, restraining their exploration over gas storage applications. Herein, a substituent strategy has been proposed and employed to generate three robust single-crystal 2D COFs isomers with atom-resolution structures determined by 3D electron diffraction. Among three isomers, a precise engineering of their interlayer distance affords the highest Brunauer-Emmett-Teller surface area of ~2100 m² g^-1 and the largest pore volume of 1.40 cm³ g^-1 for the desolvated GZU-1. This COF shows the highest total volumetric methane uptake of 240 cm³ (STP) cm^-3 at 273 K and 100 bar among 2D COFs, even comparable with those for excellent 3D MOFs. This work not only delivers unique insight into the design of 2D single-crystal COFs by interlayer stacking regulation, but also promotes the application of highly porous 2D COFs in gas storage.