Joseph J. Richardson, Commonwealth Scientific and Industrial Research Organization (CSIRO), Clayton, Victoria, Australia, Paolo Falcaro, Graz University of Technology, Austria, and colleagues have shown that gravitational force (g) influences the formation of crystals in metal-organic frameworks (MOFs). Controlling the size and morphology of MOFs is interesting for both fundamental and applied science.
The team investigated the effect of varied g (< 1, 1, 20, 50, and 100) during the crystallization of different MOFs (ZIF-8, Tb2(BDC)3, and HKUST-1) in solution. A high-gravity environment was generated by using centrifuges to spin samples. To circumvent expensive International Space Station experiments for the low-gravity experiments, the team had the idea to jump out of a plane while holding syringes and doing the experiments. This experiment was performed by several team members.
The obtained MOFs were investigated using dynamic light scattering (DLS), X-ray scattering (SAXS and WAXS), and scanning electron and optical microscopy (SEM and OM, respectively). The results proved that high g (g = 20) causes the formation of smaller MOF crystals. Low g (g < 1) led to larger crystals likely governed by facet-oriented crystal fusion due to the reduced molecular transport of precursors in solution that would typically occur due to convection.
In addition, the team claims that they have established “unique experimental protocols for low-cost low-g experimentation that should increase access to low-g experiments for the MOF community, and also the crystal community at large”. Their study “adds a new tool for controlling MOF morphology during synthesis”.
- Controlling the Growth of Metal-Organic Frameworks Using Different Gravitational-Forces,
Joseph J. Richardson, Kang Liang, Fabio Lisi, Mattias Björnmalm, Matthew Faria, Junling Guo, Paolo Falcaro,
Eur. J. Inorg. Chem. 2016.
Video: Skydiving gives the right low-gravity environment for the crystallization of different MOFs. © University of Melbourne