Enhancing Gas Adsorption in Three-Dimensional Covalent Organic Frameworks via Conformational Effects

Three-dimensional covalent organic frameworks (3D COFs) are regarded as promising gas adsorption materials due to their high surface areas and considerable porosity. However, the complex interpenetrated structures and relatively weak adsorption interactions prevent 3D COFs from fully exploiting their porous advantages in gas adsorption. Here, by leveraging conformational effects, we constructed a noninterpenetrated 3D COF with pts topology, exposing adsorption sites with higher sorption heat and achieving enhanced hydrogen uptake capacity. The noninterpenetrated 3D COF (pts-TFPA-TA) displayed a surface area of 2458 m2/g, significantly higher than that of the 5-fold interpenetrated pts topology 3D COF (pts-TFPA-BA, 1456 m2/g). Furthermore, the exposure of abundant imine (–C═N–) and vinyl (C═C) groups provides additional high-energy adsorption sites, facilitating hydrogen adsorption. The hydrogen capacity of pts-TFPA-TA reached 2.14 wt % at 1 bar and 77 K, whereas the total hydrogen uptake was 6.12 wt % at 70 bar. The physical adsorption mechanism, free from chemical reactions, ensured excellent cycling performance; the adsorption capacity of pts-TFPA-TA remained virtually unchanged after 10 cycles under high-pressure conditions (35 bar). This strategy of conformationally tuning 3D COFs at the microstructural level offers an alternative pathway for enhancing the gas adsorption performance of the COFs.