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Creation of tiny defects in ZIF-8 by thermal annealing to improve the CO2/N2 separation of mixed matrix membranes

Lai, Wen-Hsiung, Zhuang, Guo-Liang, Tseng, Hui-Hsin, Wey, Ming-Yen
Journal of membrane science 2019 v.572 pp. 410-418
annealing, artificial membranes, carbon dioxide, chemical bonding, crystal structure, moieties, nanoparticles, nitrogen, permeability, porosity, surface area, temperature
Thermal-annealed ZIF-8 nanoparticles were added into poly(styrene-co-butadiene) (SBC) to improve the permselectivity of mixed matrix membranes (MMMs). After thermal annealing process, polar atoms were produced by the broken Zn–N bond in the ZIF-8 framework. These polar atoms were beneficial in promoting the affinity toward CO2 and improved the permselectivity of the MMMs. Thermal annealing post-treatment also affected the crystallinity, functional group, and framework structure of ZIF-8. When annealing at mild temperature (300 °C), the tiny defect of ZIF-8 framework developed by removing impurity from ZIF-8 framework and broken Zn-N bond, which is benefit for creating surface area, window pore size, and un-paired –N bond, and thus improving the crystallinity. Compared with the raw-ZIF-8 MMMs, the CO2 permeability and CO2/N2 selectivity of annealed ZIF-8 MMMs enhanced because of the polar atoms produced after annealing process. The MMMs exhibited the best gas permeation performance when the annealed ZIF-8 loading weight was 20 wt%. Compared with the pure SBC membrane, CO2 permeability increased from 13.48 barrer to 39.74 barrer, and CO2/N2 selectivity almost doubled from 11.91 to 22.00.