Crosslinking two-dimensional metalloporphyrin (Me-TCPP) nanosheet with poly(ethylene) glycol semi-interpenetrating polymer network for ultrahigh CO2/N2 separation selectivity via “rubber-band” straightening effect

To efficient separate carbon dioxide from power plant flue gas, three two-dimensional (2D) metalloporphyrin (Me-TCPP) nanosheets, Zn-TCPP, Cu-TCPP, and Ni-TCPP are crosslinked with poly(ethylene) glycol (PEO) semi-interpenetrating polymer via “rubber-band” straightening effect. Dispersion-corrected periodic density functional (DFT-D2) calculation reveals that the lowest N4-Metalδ+···Oδ− distance (2.81 Å) and the highest binding energy (19.9 kJ mol−1) are obtained between CO2 molecule and metalloporphyrin center (Zn–N4), as well as the lowest O4-Metalδ+···Oδ− distance (4.68 Å) and the highest binding energy (18.8 kJ mol−1) on metal cluster (Zn–O4). The 2D Zn-TCPP nanosheet with the strongest affinity toward CO2 molecule generates Zn2+-CO2 complex to remarkably boost CO2 solubility in mixed matrix membrane (MMMs). Thus, 2.5 wt% Zn-TCPP nanosheet incorporated PEO-based MMMs dramatically promotes CO2 permeability to 198 Barrers and ultrahigh CO2/N2 selectivity to 81. A novel “rubber-band” straightening effect is found and verified, which is induced by abundant interfacial coordination bonds between metal ions in nanosheets and ester groups (O–CO) in PEO polymer chains, the strong Me–O–CO interaction sites hold polymer chains and lead to their regular rearrangement. Owing to the abundant PEG groups in PEGMEA macromolecule chains, incorporating 1 wt% Zn-TCPP nanosheet into crosslinked XLPEGDAcoPEGMEA polymer achieves the highest CO2 permeability of 398 Barrers.