Highly structured metal-organic framework nanofibers for methane storage

Porous materials such as metal-organic frameworks (MOFs) with high theoretical volumetric gas uptake capacity are promising materials for gas storage and separation, but the structuring for practical applications is challenging. Herein, we report a general and feasible strategy to combine electrospinning with a phase conversion method to decorate polyacrylonitrile nanofibers (PAN NFs) with Cu-MOF (HKUST-1). The strategy is based on the combination of surface pretreatment of the NFs with Cu(OH)2 and a subsequent phase conversion into HKUST-1 crystals (PC-HKUST-1). A significant higher loading of HKUST-1 in the PAN NF matrix was achieved by the phase conversion method compared with direct electrospinning of MOF slurries or in-situ growth of MOF crystals on NFs. As a result, the hierarchical structured PC (phase conversion)-HKUST-1 NFs revealed the highest gravimetric storage capacity of 86 cm3 g−1 (STP) at 3500 kPa and 298 K for methane (CH4), which is higher than other HKUST 1 NFs reported previously. The improved CH4 uptake can be explained by the high loading of HKUST-1 due to the high availability of Cu-ions localized on the surface of the NFs during the phase conversion process, resulting in high surface area and excellent gas access of the phase converted HKUST-1. Thus, the developed strategy of structuring MOFs could be of interest for the fabrication of tailor-made MOF NF architectures for other energy and environmental applications.