Improving CO2 separation performance of PVAm membrane by the addition of polyethylenimine-functionalized halloysite nanotubes

Mixed matrix composite membranes (MMCMs) integrate the merits of inorganic and organic materials, but the tortuous transport passageways bring about large transfer mass resistance for gas transport. Herein, we prepared polyethylenimine-functionalized halloysite nanotubes (PEI-HNTs) by the electrostatic self-assembly of positively charged polyethylenimine and negatively charged halloysite nanotubes. Blending as-obtained PEI-HNTs with polyvinylamine (PVAm), MMCMs were prepared by casting above mixed solution on the top of ultrafiltration polysulfone (PSf) support. PEI-HNTs had good miscibility with PVAm due to hydrogen bonding. MMCMs (1 wt% PEI-HNTs loading) exhibited exceptional separation performance (CO2 permeance: 179 GPU; CO2/N2 selectivity: 127.9), respectively, which were 1.4 and 2.3 times that of MMCMs embedding with 1 wt% HNTs. Noticeably, its value was beyond those of MMCMs incorporating with reported hollow tubular filler as well as other shape filler. This is due to the fact that PEI on the surfaces of HNTs provides a lot of amine carriers, which facilitate CO2 transport. More importantly, the transport passageways are continuous, thus presumably reducing the CO2 transfer resistance compared to other shape inorganic material filled-MMMs. Besides, resultant MMCMs revealed desirable stability for over 360 h, with a CO2/N2 mixture as feed gas. Remarkably, it maintained superior gas separation performance (CO2 permeance of 126 GPU; CO2/N2 selectivity of 88.6) under the acidic conditions.