0D-on-2D MOF-Based Membranes for Enhanced Helium Separation

Metal–organic framework (MOF) membranes are promising for helium (He) separation, but further improvement of the selectivity is often constrained due to the lack of precise regulation of pore size based on the single-component MOFs. Herein, we designed a 0D-on-2D MOF-based composite membrane through the assembly of 0D ZIF-67 and 2D Ni3(HITP)2, followed by the coverage of polyvinylpyrrolidone (PVP). Such a membrane features a dense 0D-on-2D MOF layer on the support, with a PVP layer permeated within the pores of the support. In this form, the 0D ultramicroporous architecture provides precise molecular sieving, and the 2D structure offers continuous transport shortcuts. Simultaneously, the polymer PVP was used to enhance the adhesion between the MOF layer and the substrate, thereby improving the integrity of the membrane. The prepared Ni3(HITP)2@ZIF-67 composite membrane achieves a He/CH4 selectivity of 63.2, an 8-fold enhancement over its single-component counterparts. The overall performance is competitive among reported MOF membranes. In the three-stage membrane process, He could be enriched from 1% to 99.9%, implying the potential for He purification. Moreover, the membrane can be fabricated at a diameter of up to 15 cm and maintains stable performance under 180° bending, demonstrating both scalability and flexibility. This work would bring inspiration for the engineering of highly selective gas separation membranes based on MOF materials.