A Poly(tetrafluoroethylene)-Based Composite Membrane with Tunable Covalent Triazine Framework and Polyaniline Modification for Efficient CO2 Separation

The increasing emission of carbon dioxide (CO2), which is the main component of greenhouse gases, has led to a series of global environmental problems. Membrane separation technology, which is characterized by low energy consumption, minimal pollution, and simple operation, has been widely applied in CO2 gas separation. The development of high-performance gas separation membrane is imperative, and the development of materials and membrane preparation technology needs to be explored. In this study, covalent triazine framework (CTF-1) is synthesized by combining trifluoromethanesulfonic acid (CF3SO3H) and terephthalonitrile (DCB), and then a PTFE/CTF-1 composite membrane is fabricated by the spin coating method with CTF-1 as the selective layer and poly(tetrafluoroethylene) (PTFE) as the support layer. The nitrogen-rich framework in CTF-1 acts as a selective layer, which enables to interact with CO2 through dipole–quadrupole interaction to preferentially adsorb CO2, but also capitalizes on the strong stability and porous structure of the PTFE membrane. By regulating the spin coating speed, the selective layer thickness is regulated, and a series of CTF-1 with distinct gas separation performance are achieved. When the spin coating speed is 3000 rpm, the PTFE/CTF-1 composite membranes show the best gas separation performance with a CO2 permeance of 548 GPU (unit of membrane permeance, 1 GPU = 10–6 cm3(STP)/(cm2·s·cmHg)) and a CO2/N2 selectivity of 17. Meanwhile, an exploratory fabrication of PTFE/CTF-1/PANI composite membranes is proceeded, followed by regulating the polymerization time to acquire an optimal gas separation performance with a CO2 permeance of 301 GPU and a CO2/N2 selectivity of 36.