BESSY II: New insights into switchable MOF structures at the MX beamlines
View into a MOF crystal exemplified by DUT-8. The massive pores are clearly discernible. © TU Dresden
Metal-organic framework compounds (MOFs) are widely used in gas storage, material separation, sensor technology or catalysis. A team led by Prof. Dr. Stefan Kaskel, TU Dresden, has now investigated a special class of these MOFs at the MX beamlines of BESSY II. These are "switchable" MOFs that can react to external stimuli. Their analysis shows how the behaviour of the material is related to transitions between ordered and disordered phases. The results have now been published in Nature Chemistry.
Metal-organic framework compounds (MOFs) consist of inorganic and organic groups and are characterised by a large number of pores into which other molecules can be incorporated. MOFs are therefore interesting for many applications, for example for the storage of gases, but also for substance separation, sensor technology or catalysis. Some of these MOF structures react to different guest molecules by changing their structures. They are thus considered switchable.
One of these is "DUT-8", a material that has now been studied at the MX beamlines of BESSY II. "MOF crystals can be analysed very well at the MX beamlines," says HZB expert Dr. Manfred Weiss, who heads the MX team. “MOF crystals have many things in common with protein crystals. For example, both are interspersed with large pores, which are filled with liquid in the protein crystals, while those in MOFs provide space for guest molecules," Weiss explains.
"The diffraction patterns that DUT-8 showed on the HZB-MX beamlines were extremely complex. We were now able to attribute this to various transitions between ordered and less ordered phases," explains Stefan Kaskel. The enclosed guest molecule directs the network into one of over a thousand possible disorder configurations. The results contribute to a better understanding of switching processes and gas exchange reactions in such MOF structures, so that future functional MOF materials can be developed in a targeted manner.
The investigations were supported by the DFG programme (FOR2433).
- Perovskite solar cells from the slot die coater - a step towards industrial productionSolar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
- Superstore MXene: New proton hydration structure determinedMXenes are able to store large amounts of electrical energy like batteries and to charge and discharge rather quickly like a supercapacitor. They combine both talents and thus are a very interesting class of materials for energy storage. The material is structured like a kind of puff pastry, with the MXene layers separated by thin water films. A team at HZB has now investigated how protons migrate in the water films confined between the layers of the material and enable charge transport. Their results have been published in the renowned journal Nature Communications and may accelerate the optimisation of these kinds of energy storage materials.
- Electrocatalysis under the atomic force microscopeA further development in atomic force microscopy now makes it possible to simultaneously image the height profile of nanometre-fine structures as well as the electric current and the frictional force at solid-liquid interfaces. A team from the Helmholtz-Zentrum Berlin (HZB) and the Fritz Haber Institute (FHI) of the Max Planck Society has succeeded in analysing electrocatalytically active materials and gaining insights that will help optimise catalysts. The method is also potentially suitable for studying processes on battery electrodes, in photocatalysis or on active biomaterials.