Inorganic Pillar Center-Facilitated Counterdiffusion Synthesis for Highly H 2 Perm-Selective KAUST-7 Membranes.

Fluorinated metal-organic framework materials (NbOFFIVE-1-Ni, also referred to as KAUST-7) have attracted widespread attention because of their high chemical stability and thermal stability, outstanding tolerance with water and H 2 S, and high CO 2 -adsorption selectivity over H 2 and CH 4 . KAUST-7 was expected to be a new membrane material candidate for H 2 /CO 2 separation because of the hindered permeation of CO 2 resulting from the interaction between CO 2 and (NbOF 5 ) 2- of the KAUST-7 framework. A highly H 2 perm-selective KAUST-7 membrane was first achieved using a novel strategy of inorganic pillar center-facilitated counterdiffusion (IPCFCD) proposed by us. The IPCFCD method not only effectively avoided the corrosion of hydrofluoric acid to α-Al 2 O 3 tubes in the process of preparing KAUST-7 membranes, but also better reduced grain boundary defects because of the faster nucleation rate and resultant high crystallinity. The KAUST-7 membrane exhibited a high H 2 /CO 2 separation factor (SF) of 27.30 for the 1:1 H 2 /CO 2 binary gas mixture with a high H 2 permeance of 5.30 × 10 -7 mol m -2 s -1 Pa -1 under ambient conditions and a slight decrease of the H 2 /CO 2 SF with increasing operation temperature and presence of steam. This study highlighted the importance of pre-synthesizing inorganic pillar centers (NiNbOF 5 intermediate) and the innovation of a membrane formation process for synthesizing polycrystalline KAUST-7 membranes. Most important of all, our study provided a novel approach to overcome the challenge in fabricating metal-organic framework membranes containing corrosive reactants for the corresponding supports.