Porous Membranes and Sensor Materials
Metal-organic framework (MOF) membranes have the potential to be a key technology to fight climate change to reach the EU climate goals until 2050. Membranes allow a continuous separation of gases and are able to reduce CO2 by (a) an active separation of CO2 from waste gases and (b) by making different production cycles green through a substitution of cryogenic gas distillation columns. Membranes using MOF and COF can also tackle other challanges of mankind, such as saltwater desalination and wastewater treatment to provide clean drinking water.
Stimuli Responsive Membranes
The synthesis of MOFs and COFs is usually approached solvothermally on a ceramic membrane support . However, it can be taken to the next level by using liquid phase epitaxy (LPE), which can produce a unit cell precision coating, even on a rough, ceramic support. This powerful technology also allows to build up hierarchical MOF membranes, combining the separation parameters of the component MOFs. To obtain a continuous gas separation tunability of MOF membrane films, which could eventually lead to performance boosts, the application of external stimuli in-situ is a novel technique. Choosing the right MOF and the correct external stimulus can result in a selectivity tuning, for example by irradiation with light, or by “defibrillation” of the lattice by electric fields leads to enhanced molecular sieving.
Porous Liquids and Mixed Matrix Membranes
A novel class of materials are Porous Liquids (PLs), being a colloidal MOF solution in which the solvent molecules cannot penetrate the pores of the framework. Thus, the nanocrystals remain empty in a solution. PLs can be used as processable MOF systems, that are highly monodisperse, allowing extreme high loading into gas separating polymers. MOF-fillers in polymeric matrices are called Mixed Matrix Membranes (MMMs), which are the industrially relevant types of membranes, due to their low costs and high processability.
Using Lanthanides for the synthesis of MOFs and thin films of MOFs lead to unique and extraordinary properties. On the one hand, these materials can be extremely temperature stable up to 620 °C, but also luminescent and sensitive to analyte gases. This in mind, Ln-MOFs are perfect candidates for gas separation and sensors. Using these materials for polymer-filler composite membranes is a novel approach followed by the research group.
A great challange of today, becoming more and more important in the future, is to provide clean drinking water to the people. Therefore, wastewater treatment and desalination of seawater become more and more important. We mainly focus on wastewater treatment via molecular sieving of dye molecules from water. High flux and high separation values are important in order to achieve high performance membrane systems. Two separation techniques are of interest here, which is cross-flow continuous filtration and dead-end batch filtration. Whereas the first method is relying on molecular sieving, the latter one is relying on the adsorptive properties of the membrane (filler) material.