Dynamic processes in porous materials in the form of powder or films are crucial for their potential applications, which range from sensor technology to molecular storage and separation. Furthermore, dynamic processes are the key to the production of smart materials which dynamically respond to external stimuli. Surface-mounted metal-organic frameworks, SURMOFs, are particularly fascinating porous films of metal-organic frameworks, MOFs, prepared in a well-defined layer-by-layer method. The interaction of the guest molecules with the framework and the diffusion of the guest molecules in the pores are among the research interests of the work group.
Smart Nanoporous Coatings-Thin Films of Photoswitchable Metal-Organic Frameworks
|The remote control of physical and|
|chemical properties is one of the
|key challenges for intelligent, functional
|materials. The great potential of thin
|porous films of MOFs containing linkers
|with photoswitchable motieis is shown.
|The state of the photoswitchable group
|such as azobenene, can be reversible
|switched by light of different wavelenghts.
|This photoswitching influences the
|interaction between the host framework
|and the guest molecules.
A few applications are:
• Closing and opening the pores and demonstrating the remote-controlled release from a nanoporous container. DOI: 10.1021/nn405469g
• Membranes with photoswitchable permeation and tunable molecular separation, see figure, DOI: 10.1038/ncomms13872.
• Remote-controllable proton conduction of the guest molecules, having potential applications in switchable sensors and biological information transformation, DOI: 10.1002/adma.201706551.
Mass Transfer in Thin Films of Metal-Organic Frameworks
The loading with guest molecules is the key for most applications of nanoporous materials, such as MOFs. Using a quartz crystal microbalance (QCM), time-resolved infrared (IR) or UV-vis spectroscopy, we investigate the mass transfer of various molecules in the nanoporous framework under different conditions:
• The uptake of vapor at various temperatures, allows
determination of adsorption enthalpies and activation
energies, DOI: 10.1039/c3cp50578b.
• Comparison of liquid- and gas-phase diffusion,
• Multi-component diffusion, see figure,
• Impact of framework defects on the mass transfer,
• Adsorption and diffusion of chiral molecules in
homochiral MOFs, DOI: 10.1039/c5cc02706c.
Defects in Metal-Organic Frameworks
Similar to other semiconducting materials, in addition to the chemical properties, the optical and electronic properties of MOFs depend critically on defect densities and defect types. This is investigated in different projects:
• Improving the synthesis increases
the transparency of MOFs of type HKUST-1,
• MOF defects act as color centers,
• MOF defects hinder the mass transfer,