Increasing the Stability of Metal–Organic Frameworks by Coating with Poly(tetrafluoroethylene)

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Abstract
When compared to industrially stable zeolites, the instability of metal–organic frameworks (MOFs) has been denounced by researchers. Boosting the stability of existing MOFs is highly important for practical applications. In this report, we develop a new strategy to prepare MOFs/poly(tetrafluoroethylene) (PTFE) composites, which can highly improve the chemical, pressure, and photostabilities of zeolitic imidazolate framework (ZIF)-8. Composite materials were prepared by a physical blending of ZIF-8 and PTFE emulsion with different ratios and annealing at 370 °C. Transmission electron microscopy (TEM) studies reveal that the nanoparticles of ZIF-8 are coated by PTFE to form the composite materials. Upon mixing with 20 or 50 wt % PTFE, the ZIF-8/PTFE materials show a superhydrophobic property with water contact angles of around 156°. Pristine ZIF-8 is not stable in water with stirring under acidic, basic, and irradiation conditions, while the ZIF-8/PTFE materials are stable under the same conditions. The ZIF-8/PTFE materials can also maintain their crystalline structure after being compressed with a 10 MPa pressure, while pristine ZIF-8 changes to an amorphous solid after the same pressure treatment. Using water as a solvent, ZIF-8/PTFE can be used as a highly efficient and recyclable catalyst for Knoevenagel reaction at room temperature. The successful preparation of stable ZIF-8/PTFE composite materials provides a useful method to enhance the chemical, pressure, and photostabilities of MOFs.
Funding Information
  • Guangdong Provincial Department of Science and Technology (2019B030302009)
  • Guangzhou Municipal Science and Technology Program key projects (202002030411)
  • Jinan University
  • National Natural Science Foundation of China (21701049, 21871172, 22171106)
  • Natural Science Foundation of Guangdong Province (2214050003096)

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