Constructing multi-dimensional transport pathways by mixed-dimensional fillers in membranes for efficient CO2 separation

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Mixed matrix membranes (MMMs) with mixed-dimensional fillers can take simultaneously advantages of the different-dimensional materials, and they hold the potential in exhibiting excellent CO2 separation performance. In this study, the mixed-dimensional fillers of NiCo-layered double hydroxide-decorated polypyrrole nanotubes (PNT@NiCo-LDH) were synthesized and incorporated into Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. PNT@NiCo-LDH played a vital role in MMMs. PNT@NiCo-LDH can take the advantages of the tubular structure of PNT, the lamellar structure of LDH, the hollow nanocage structure of NiCo-LDH, constructing 1D/2D/3D CO2 transport pathways in MMMs, respectively. Thus, the construction of multi-dimensional (1D/2D/3D) CO2 transport pathways could synergistically improve CO2 separation performance of MMMs. Besides, the CO2-affinity groups (amino groups and hydroxyl groups) and bimetallic sites (Ni and Co) on PNT@NiCo-LDH effectively accelerated CO2 selective transport in MMMs, increasing CO2/CH4 selectivity. Therefore, the as-prepared MMMs exhibited an excellent CO2 separation performance. The Pebax/PNT@NiCo-LDH-5 MMM showed the optimum CO2 permeability of 513 ± 10 Barrer and CO2/CH4 separation factor of 39 ± 0.5. This work implied that the construction of multi-dimensional CO2 pathways by mixed-dimensional fillers were an effective strategy for efficient CO2 separation in MMMs.