Polymer-incorporated modified halloysite nanotubes for efficient CO2/N2 separation

Mixed-matrix membranes (MMMs) as one of solid sorbents for carbon dioxide (CO ₂ ) separation face the challenge of merging efficient separation with economical preparation process using scalable raw material. Halloysite nanotubes (Hal) with unique one-dimensional gas transmission channels have great prospect in MMMs for gas separation. However, the insufficient porosity of Hal has restricted further development of CO ₂ separation performances. Herein, a facile and efficient modification approach was carried out, involving successive treatments of calcination and selective leaching. The resulting nanotubes with continuous channel systems (CA-Hal) are embedded in poly(ether- block -amide) for the preparation of mixed-matrix membranes with enhanced gas transport. The performances of MMMs with modified nanotubes as inorganic fillers obtained by different modification methods (calcination, selective leaching, and a combination of calcination and selective leaching) were specifically discussed. CA-Hal with the highest specific surface area and certain surface energy has an excellent potential as inorganic fillers, which can be uniformly dispersed in the polymer matrix to form interfacial channels, preventing the particle agglomeration and producing non-selective interfacial defects. The hierarchical porous structure of CA-Hal can serve as fast gas transport channels in MMMs for efficient CO ₂ diffusion and enhanced separation. The MMMs containing 5 wt% CA-Hal have demonstrated excellent CO ₂ permeability (179.5 Barrer), CO ₂ diffusivity (17.56 10 ⁻⁷ cm ²·S ⁻¹) and CO ₂/N ₂ selectivity (98.7). In addition, the prepared MMMs exhibits improved mechanical properties compared with the pure membrane without inorganic fillers.