Hierarchically Porous Graphene/ZIF-8 Hybrid Aerogel: Preparation, CO2 Uptake Capacity, and Mechanical Property.

A hierarchical zeolitic imidazole framework (ZIF) combining a micropore with a mesoporous structure is desirable to enhance mass transport and gives rise to novel applications. Here, hierarchically porous graphene/ZIF-8 hybrid aerogel (GZAn) materials were successfully prepared by a two-step reduction strategy and a layer-by-layer assembly method. To avoid a tedious dry step and the use of an energy-consuming freeze-drying technology, a reduced graphene oxide hydrogel with different reduction degrees was chosen as a template to grow ZIF-8 crystals in situ. The parameter of density and elemental analysis was adopted to calculate the amount of ZIF-8 in GZAn materials for different assembly cycles. The distribution of micropores and mesopores of GZAn materials was controlled by changing the loading of ZIFs in GZAn materials. Furthermore, GZA8 materials showed enhanced CO2 uptake capacity (0.99 mmol g-1, 298 K, 1 bar) than pure ZIF-s crystals and pure graphene aerogels, showing an excellent synergistic effect of hierarchical pore structures. Meanwhile, with the increase of ZIF-8 loading, the mechanical robustness of GZAn was uplifted obviously. This work provides an efficient method to prepare hierarchically porous ZIFs-based materials with good CO2 uptake capacity and tunable mechanical robustness.