Crosslinking two-dimensional metalloporphyrin (Me-TCPP) nanosheet with poly(ethylene) glycol semi-interpenetrating polymer network for ultrahigh CO2/N-2 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 N-4-Metal(delta+)center dot center dot center dot O delta- distance (2.81 angstrom) and the highest binding energy (19.9 kJ mol(-1)) are obtained between CO2 molecule and metalloporphyrin center (Zn-N-4), as well as the lowest O-4-Metal(delta+)center dot center dot center dot O delta- distance (4.68 A) and the highest binding energy (18.8 kJ mol(-1)) on metal cluster (Zn-O-4). 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 ultra-high CO2/N-2 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-C=O) in PEO polymer chains, the strong Me-O-C=O 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.