Thermally induced transformation of ZIF-8 to ZnF2 in CNT/PVDF composite membranes for tunable porosity and gas transport

Gas separation membranes offer an energy-efficient alternative to conventional separation technologies. However, achieving high permeability and selectivity simultaneously remains a challenge. In this work, we fabricate thin composite membranes composed of carbon nanotubes (CNTs), polyvinylidene fluoride (PVDF), and zeolitic imidazolate framework-8 (ZIF-8), and investigate the effect of heat treatment on their structural and transport properties. Thermal analysis, XRD, and XPS reveal that PVDF decomposition releases HF, which reacts with ZIF-8 to form ZnF 2 , inducing pore formation and altering the polymer structure. Gas permeation measurements indicate that ZIF-8 incorporation enhances overall permeability, while heat treatment induces a transition in transport mechanism from solution-diffusion to a mixed regime consistent with molecular sieving and Knudsen diffusion. For example, the H 2 permeability of CNT/PVDF membrane increased by more than an order of magnitude, from 0.16 to 32.6 Barrer for CPZ73(330) while also increasing in selectivity against larger molecules. Unlike conventional mixed-matrix membranes where fillers remain inert, ZIF-8 acts as a reactive component that changes the polymer microstructure. Overall, this work demonstrates a scalable, single-step approach for generating tunable gas transport pathways and offers a general framework for thermally reactive polymer–MOF membranes for industrial separations. • Controlled thermal treatment of CNT/PVDF/ZIF-8 MMMs triggers PVDF dehydrofluorination and in-situ ZIF-8 → ZnF₂ conversion, generating hierarchical porosity and shifting transport from solution–diffusion to a hybrid molecular sieving/Knudsen regime. • CPZ73(330) showed increase in both permeability and selectivity compared to CP membrane with H 2 permeability increasing from 0.16 to 32.6 Barrer while also increasing H 2 /N 2 selectivity from 29.7 to 54.9 and H 2 /CO 2 selectivity from 1.1 to 4.8. • Multimodal characterization (TGA/DSC, XRD, XPS, BET, density measurement, SEM/EDS) verifies HF-mediated conversion and microstructural evolution. • Targeted annealing drives polymer–MOF chemical interactions driving structural changes that can improve both permeability and selectivity. • This work introduces a general strategy for thermally reactive polymer–MOF systems to engineer tunable porosity and gas transport properties.