Synthesis of hydrolytically stable metal-organic frameworks by control of inner surface hydrophobicity

• Applicant: Professor Dr. Stefan Kaskel
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 245128070

The goal of the proposed project is to use the modular construction principles of MOFs for the synthesis of new, hydrolytically stable framework structures with large empty spaces that are accessible to gas molecules. As a rational concept two strategies will be followed: a) enhancing linker metal bond strengthsb) synthesis of MOFs with hydrophobic inner surface To reach these goals the voids in these materials will be decorated with hydrophobic groups such as trifluoromethyl. Overall, the research involves not only the synthesis and structural studies, but also a quest to understand the fundamental aspects of water adsorption in relation to water-solid reactions.To enhance the hydrolytic stability of MOFs, different strategies will be followed: the group of Prof. Bharadwaj (India) will use ligands with donor groups like pyridine or imidazole in addition to carboxylate, to enhance the linker-metal bond strength in MOFs. Additionally, the introduction of hydrophobic groups (such as CF3) will be tested, to create the hydrophobic, water-repellent surface on the one hand, and to enhance the adsorption capability for hydrophobic molecules (hydrocarbons, hydrogen) on the other hand. The German group will focus on the synthesis of mesoporous Zr-based MOFs in combination with introduction of hydrophobic monocarboxylic acids, which should play a role of cluster protecting shields. The mesoporosity on the other hand is needed to achieve the high storage capacity in high pressure gas storage. Investigation of adsorption properties of MOFs prepared in both working groups, as well as systematic study of influence of incorporated functional groups on adsorption properties and isosteric head of adsorption will be performed in the group of Prof. Kaskel.Key scientific goals:Strategic goals:Identification of hydrolytically stable MOFs;Control of surface hydrophobicity;Enhancement of hydrolytic stability;Water adsorption mechanisms on MOFs with different hydrophobic/hydrophilic surface. Linker chemistry:Design and synthesis strategy for linkers bearing donor groups like pyridine or imidazole in addition to carboxylate groups;Integration of hydrophobic functional groups into MOFs; Modular linker concepts for systematic tailoring of specific interactions.Synthesis methods and structure analysis:Integration of new linkers into stable porous networks;Synthesis of single crystals;Single crystal X-ray structural analysis; Up-scaling for gas adsorption experiments.Porosity and Characterization:Adsorption techniques in solution (dye adsorption) and gas phase (nitrogen at 77K) to prove pore accessibility; Water vapor adsorption experiments for study of hydrophobicity degree of MOFs.Functions:High pressure gas storage for different gases (H2, CO2, CH4, Kr); Gas separation (selective gas adsorption);n-Butane adsorption experiments to prove the adsorption ability for hydrophobic species.

• DFG Programme: Research Grants
• International Connection: India
• Partner Organisation: Department of Science and Technology (DST)
• Participating Person: Professor Dr. Parimal K. Bharadwaj