Tuning crystalline structure of zeolitic metal–organic frameworks by supersonic spraying of precursor nanoparticle suspensions

The deposition of sodalite zeolitic imidazolate framework-7 (ZIF7) films by a supersonic cold-spraying technique was successfully accomplished for the first time. The high-speed impact of supersonic cold spraying increased the monodispersity of the ZIF7 crystalline structure. However, the intensity of the structural change decreased with increasing the amount of nylon in the ZIF7 suspension. Mitigating phase changes in ZIF7 occurred by the impact dampening conferred by the polymeric nature of nylon, which preserved the original three-dimensional crystalline structure of ZIF7. The inclusion of N,N-dimethylformamide (DMF) in a nylon–ZIF7 suspension improved the dispersion of ZIF7 nanoparticles, which in turn eliminated the dampening effect from the nylon and recovered the distinctive monodispersity arising from the high-speed impact. This characteristic was observed at all impact speeds for ZIF7 suspensions containing DMF. We show that high-rate cold spraying of ZIF7 particles can be combined with nylon and other pressure-transmitting media to control the formation of three distinctive phases. The unique capability to tune the crystalline structure of ZIF7 allows customization of the film functionality for specific applications.