Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - GROWMOF (Modelling of MOF self-assembly, crystal growth and thin film formation)

Teaser

Metal-organic frameworks (MOFs) constitute one of the most exciting developments in recent nanoporous material science. Synthesised in a self-assembly process from metal corners and organic linkers, a near infinite number of materials can be created by combining different...

Summary

Metal-organic frameworks (MOFs) constitute one of the most exciting developments in recent nanoporous material science. Synthesised in a self-assembly process from metal corners and organic linkers, a near infinite number of materials can be created by combining different building blocks allowing to fine tune host guest interactions. MOFs are therefore considered promising materials for many applications such as gas separation, drug delivery or sensors for which MOFs in form of nanoparticles, composite materials or thin films are required. For MOFs to realise their potential and to become more than just promising materials, a degree of predictability in the synthesis and the properties of the resulting material is paramount and the full multiscale pathway from molecular assembly to crystal growth and thin film formation needs to be better understood. Molecular simulation has greatly contributed to developing adsorption applications of MOFs and now works hand-in-hand with experimental methods to characterise MOFs, predict their performance and study molecular level phenomena. In contrast, hardly any simulation studies exist about the formation of MOFs, their crystal growth or the formation of thin films. Yet such studies are essential for understanding the fundamentals which will ultimately lead to a better control of the material properties. Building on my expertise in molecular modelling including the development of methods to model the synthesis of porous solids, we will develop new methods to study:

1. the self-assembly process of MOFs under synthesis conditions
2. the formation of nanoparticles
3. the integration of MOF nanoparticles into composite materials and the self-assembly into extended structures
4. the layer-by-layer growth of thin films

At the end of the project we will have transformed our understanding of how MOFs form at a variety of length scales and opened up new research directions for the targeted synthesis of MOFs fit for applications.

Work performed

We have developed methods to describe the self-assembly process from metal corners and organic linkers that will allow us to describe the formation of different MOF structures under synthesis conditions. To start with and to prove the concept we have chosen a relatively simple model system where small changes in the synthesis condtions such as a change in the ratio of metal to linker or temperature lead to very different structures ranging from one-dimensional chains to two- and three-dimensional extended networks. We have successfully modelled the formation of different structures from different ratios of metals to linkers. An important part of the work is to look at the assembly and growth of matl-organic frameworks at different lenght scales. On the ab initio level (i.e. a more precise level) we studied which species are present in the synthesis soluion which will form an important input into the simulation of the aseembly of such building blocks into extended networks. While we can get very detailled insight into how metals and linkers interact at the ab inito level, we can only study very small systems at this level. Therefore we are currently developing methods to translate the information we can get at this level into realistic potentials that we can use to correctly describe the assembly of the different building blocks.

Final results

Simulation studies about the formation of MOF structures are still very rare and for the first time we have been able to simulate the formation of different MOF structures by changing the synthesis conditions. This is an important step to rationalise how the synthesis conditions influence the resulting structures and will ultimately lead to greater control of the optimisation of synthesis conditions to target MOFs for specific applications such as drug delivery or the separation of high value products.