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Combinatorial Computational Chemistry A new field to tackle environmental problems

Final Report Summary - C3ENV (Combinatorial Computational Chemistry A new field to tackle environmental problems)

1. Development of Computational Screening for Molecular Framework Materials Software Environment
Molecular Framework Materials (MFM) are a class of compounds where molecular building blocks are stitched together by strong chemical bonds to form regular frameworks. Most prominent materials are metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous aromatic frameworks (PAFs). We have developed a software that allows the computational design of virtually any MFM with to-date known or unknown building block or bonding concept. This software is linked to a powerful library of molecular building blocks and network topologies. A researcher can now create a MFM based on his own molecular building blocks, or use the library to screen hundreds of thousands of MFMs to find those materials that are most suitable for a targeted application. Those materials can then be studied at a high level of theory, and ultimately scheduled for synthesis.

2. Ethanol-Water separation mechanism
Selective adsorption of ethanol and other alcohols in MOFs would allow the capture of biofuels from low-concentration mixtures. A first material showing these properties has been reported in 2007. Our computational analysis of this material showed that the mechanism is based on molecular recognition. We have extended this molecular recognition approach in MOFs and investigated possibilities to capture harmful gases, such as NOx and CO. Consequent further investigation, which is still in progress, targets in the separation of hydrocarbon isomers and ultimately in chiral separation.

3. Proton conductance in MFMs
Proton exchange membranes are very important components in fuel cells. Fuel cells can convert chemical to electrical energy at high efficiency, both for stationary and mobile applications. To enhance the efficiency, water-free proton exchange membranes that operate at low temperature are needed. These membranes must be permeable to protons, but electrically insulating and block oxygen and other gases. The state-of-the-art is Nafion, a polymer that suffers if the operation temperature approaches the boiling point of water. We have investigated alternative membrane concepts, in particular COFs with additional functional sulphonyl groups. Those show promising performance and have been realised in experiment. It remains to be investigated how the material can be created in macroscopic quantities and with high crystallinity, as one advantage of these layered COFs is their directional proton transport.

4. Surface-mounted MOFs (SURMOFs) are MOFs grown as thin film on a substrate. They are produced in a layer-by-layer fashion which allows to change the composition of the film step by step. Among the many investigations on SURMOFs we have developed a SURMOF solar cell. Here, light is absorbed by porphyrins, similar as in photosynthesis. However, the crystallinity makes the material an indirect band gap semiconductor, which allows charge carrier separation and thus enhances the efficiency.

5. Layered COFs. We were the first to report delaminated COFs, and had important contributions for proton-conducting COFs, COFs suitable for chemical sensing of explosives, and for increasing the water stability of MFMs. Exfoliated COF monolayers may become an interesting member in the family of two-dimensional materials (such as graphene) and we are currently exploring their physical properties.