Enhancing the CO2 separation performance of SPEEK membranes by incorporation of polyaniline-decorated halloysite nanotubes

Polyaniline-decorated halloysite nanotubes (PANI-d-HNTs) having a multilayer hollow tubular structure were incorporated into sulfonated poly(ether ether ketone) (SPEEK) to prepare high-performance mixed matrix membranes (MMMs) for CO2/N-2 separation. Scanning electron microscopy images revealed that PANI-d-HNTs were tightly wrapped by SPEEK chains. The strong interfacial interaction between PANI-d-HNTs and SPEEK, as confirmed by attenuated total-reflectance Fourier-transform infrared spectroscopy and differential scanning calorimetry, led to excellent miscibility between the polymer and halloysite nanotubes, which in turn, resulted in improved mechanical properties for the MMMs. The highest CO2 permeability of 1260 Barrer and a CO2/N-2 selectivity of 87 were achieved for MMMs loaded with 0.9 wt% PANI-d-HNTs; these values exceeded the Robeson's upper bound proposed in 2008, and were also much higher than those of MMMs containing 0.9 wt% HNTs, for which, a CO2 permeability of 1093 Barrer and CO2/N-2 selectivity of 74 were observed. It is proposed that PANI-d-HNTs with a multilayer hollow tubular structure can be used as high-speed facilitated channels for CO2 transport, where densely arranged secondary amine groups readily reacted with CO2 to facilitate transport in the MMMs. Importantly, durability testing indicated that MMMs loaded with 0.9 wt% PANI-d-HNTs maintained outstanding CO2 permselectivity for over 120 h, suggesting the superior stability of the membranes under mixed gas feed conditions.