Surface-engineered PIM-1 membranes for facile CO2 capture

Polymers of intrinsic microporosity (PIMs) are promising candidates for carbon dioxide (CO2) separation and capture from flue gas or natural gas. PIM-1, which has excellent gas permeation properties over the Robeson upper bound (1991), has been widely functionalized to further enhance the CO2 permeability or selectivity. In this work, a simple and readily processive surface modification method has been proposed via hydrolysis of the PIM-1 membrane. The two hydrolysis processes by the acid method, amidation and carboxylation processes, have been conducted to functionalize the surface of PIM-1 membranes forming NA-PIM-1 and CA-PIM-1 membranes. The TGA, FT-IR spectra and NMR results verify that the composition and structure inside the PIM-1 membrane remain unchanged. XPS and NMR spectra demonstrate that the nitrile group at the surface was successfully functionalized with an amine group or carboxyl group. The CO2 permeability and CO2/N2 selectivity of the NA-PIM-1 membrane both increased to 4593.2 Barrer and 28.5, respectively. Another advantage of NA-PIM-1 membranes is the coordination site from introduced nitrogen atoms with zinc ions to form NA-PIM-1-Zn, which could further react with PEI to introduce amine-rich groups on the surface of the PIM-1 membrane. The CO2/N2 selectivity of the NA-PIM-1-Zn-PEI membrane coated with PEI on the surface increases 45.4% compared to the unmodified PIM-1 membranes, with CO2 permeability decreasing only 15.5% compared to the unmodified PIM-1 membrane. The NA-PIM-1 and NA-PIM-1-Zn-PEI membranes both surpass the Robeson upper bound (2008) even under mixed gas feeding, suggesting that surface modification of PIM-1 is a promising approach for CO2 capture from natural gas and flue gas.