COF-based MMMs with light-responsive properties generating unexpected surface segregation for efficient SO2/N2 separation

The purification of sulfur dioxide (SO 2 ) from the flue gas is an urgent problem given its toxicity to humans and organisms and attendant environmental concerns. In this study, aiming at the separation of SO 2 , mixed matrix membranes (MMMs) are fabricated by incorporating covalent organic framework (COF) into Pebax 1657 polymer matrix . By strengthening the solubility-diffusion mechanism of SO 2 gas molecules, SO 2 /N 2 gas separation performance is investigated. Firstly, MMMs are fabricated by incorporating a porous framework material (TpPa-1) containing SO 2 affinity groups into the Pebax 1657 matrix as a filler. Then the azo group (Azo) is introduced into the MMMs by the method of physical blending. The MMMs with light-responsive characteristic are fabricated by introducing TpPa-1 blended with pAAB into the Pebax 1657 polymer matrix. Secondly, the SO 2 /N 2 separation performance of Pebax/TpPa-1 MMMs is improved with the increasing of filler loading. Specially, the Pebax/TpPa-1 membrane with 5 wt% exhibits the most excellent SO 2 /N 2 separation performance with SO 2 permeability of 1709 Barrer and SO 2 /N 2 selectivity of 811. The MMMs overcome the trade-off effect and achieve enhancement of SO 2 permeability and SO 2 /N 2 selectivity simultaneously. Thirdly, both the SO 2 permeabilities and SO 2 /N 2 selectivities of Pebax/pAAB@TpPa-1-5% membrane exhibit regular and reversible changes under UV–Vis light-conversion conditions, indicating that MMMs containing Azo possesses dynamic light-responsive properties. Furthermore, TpPa-1 and pAAB repel each other in the membrane because both have negative charges, resulting in the forced surface segregation of COF in the Pebax/pAAB@TpPa-1 MMMs.