DASZIF · Rational Design and Synthesis of Zeolitic Imidazolate Frameworks (ZIFs): an experimental and statistical approach

Rational Design and Synthesis of Zeolitic Imidazolate Frameworks (ZIFs): an experimental and statistical approach

Summary of research and training outcomes from DasZIF: * Identifying optimal ZIFs structures using molecular simulation: DFJ classified ZIFs in terms of pore volume, surface area, and size of windows between cavities to find structures with improved adsorption performance. Using molecular simulations, he identified three different topologies and seven specific materials: sod (ZIF-8, ZIF-65 and ZIF-90), rho (ZIF-11 and ZIF-71) and lta (ZIF-20 and ZIF-76). He localised the different adsorption sites for these materials and studied multi-component adsorption related to the purification of CH4, H2 and the capture of CO2 in these ZIFs. * Synthesis and characterisation of optimal ZIFs. In collaboration with Prof. Paul Wright, University of St. Andrews, UK, DFJ was able to synthesise five different ZIFs identified as promising materials: ZIF-8, ZIF-20, ZIF-65, ZIF-90 and ZIF-71, changing the reaction conditions by using new solvents, precursors or higher pH to activate the imidazolate rings. He obtained experimental adsorption data for the N2, CO2, CH4, Ar and H2 for these materials, adapting and validating the simulation model for ZIFs. The match of the maximum uptake between experimental and simulated values at low temperature showed the good quality and complete activation of the samples. * Understanding the occurrence of Type V isotherms in microporous MOFs. DFJ used grand canonical Monte Carlo simulation to investigate why certain MOFs show unusual Type V-sigmoidal adsorption isotherms in contrast to the expected Type I (Langmuir) isotherms. He found that the presence of Type V adsorption is caused by a fine balance between the strength of the fluid-fluid and fluid-solid interactions, which in turn is a strong function of type of fluid and the length of the linker and therefore the pore size of the material. * Flexibility in the ZIF framework caused by adsorption: One of the most exciting findings of this project was the discovery of framework flexibility in ZIFs. It has been previously observed that gas molecules with larger size than the windows between cavities are taken up in these materials. We were able to use for the first time a diamond anvil-cell experiment, used to put a material under extremely high pressures (i.e. 14,700 bar), to obtain structural models for the molecular simulation which then showed very good agreement with experimental adsorption measurements. Using in-situ synchrotron experiments at Diamond Light Source, UK, DFJ showed that the ZIF-8 structure was modified by gas adsorption uptake in the same way as it is at a very high pressure due to a swing effect in the imidazolate linkers, enlarging the pore window and giving access to the porosity and thus explaining the adsorption of large molecules. * ZIFs on industrial applications. DFJ assessed the impact of flexibility on the adsorption of different energy-related gases on ZIF-8, such as alkanes, CO2 and H2. He achieved excellent agreement between simulated and experimental results by solely adapting the UFF generic force field reducing the Lennard-Jones interaction parameter ε. The results show that two different structural configurations of ZIF-8 were needed to properly describe its adsorption performance, demonstrating that ZIF-8 is undergoing a structural change during gas adsorption. Over the duration of the project, DFJ received research training in a number of areas: the use of molecular and quantum simulation, MOF synthesis, high pressure adsorption and in-situ synchrotron XRD techniques. He attended different workshops and courses on complementary skills: Supervising postgraduate research, Funding opportunities, Introduction to management, Team working and leadership, Introduction to project management for researchers and courses in university teaching. He gained teaching experience by being a guest lecturer and demonstrator in chemical engineering. He contributed to the course design; developed his own lecture material and laboratory manual

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