Rapid synthesis of ultra-microporous metal-organic framework tubular Ni-LAP membranes for H2 separation by linker salt method

Abstract

Recently, the development of pillar-layered metal-organic frameworks (MOFs) is receiving more and more attention because of their pore surface chemistry tunability and designability. In this work, we firstly synthesized various sizes of high-quality Ni-LAP [Ni2(L-asp)2(pz)] (L-asp = l-aspartic acid, pz = pyrazine) crystals key for secondary growth by manipulating the crystal thermal dynamics and kinetics of Ni-LAP synthesis solution simply through choosing the Ni(OAc)2 as metal source and pretreatment at 40 °C, followed by the fabrication of defect-free Ni-LAP membranes as a model in a short time of 4 h using the linker salt method. It is found the pretreatment of Ni(OAc)2 precursor solution at 40 °C with continuous stirring for 6 h can effectively promote deprotonation to form 250 nm crystals. The linker salt method enables a greener and more rapid synthesis of Ni-LAP membranes, with continuous and compact Ni-LAP membranes, where soluble metal precursors and organic linking salts provide the synthesis solution a higher degree of supersaturation, both of which play an important role in the rapid preparation of Ni-LAP membranes. The preparation parameters of the Ni-LAP membranes were investigated in detail, and the results from the Ni-LAP membrane gas separation performance showed that the preferential (111) orientation membrane (M9) exhibited the best H2/CO2 separation performance with separation factor of 23.8 and H2 permeance of 2.11 × 10−7 mol m−2 s−1 Pa−1 compared to the preferential (002) orientations (M3), which may attributed to the preferential (111) orientation being at an angle to the optimal a-axis aperture perpendicular to the support thereby reducing the mass transfer resistance. Furthermore, the generation of corrosive nitric acid during the preparation process can be greatly reduced and replaced by eco-friendly potassium nitrate. The superiority of the pore structure and the remarkable stability of these MOF membranes show the potential for H2 purification. Moreover, our preparation route demonstrates the universality of preparing other isomorphs, such as Ni-LAB and Co-LAP membranes.