Dynamic Processes in Porous Films

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,

  DOI: 10.3390/ma8063767.

• Multi-component diffusion, see figure,

   DOI: 10.3390/ma8063767.

• Impact of framework defects on the mass transfer,

   DOI: 10.1038/ncomms5562.

• 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,

   DOI: 10.1016/j.micromeso.2015.02.048.

• MOF defects act as color centers, 

   DOI: 10.1021/acsami.7b12045.

• MOF defects hinder the mass transfer,

   DOI: 10.1038/ncomms5562.