Transparent films of metal-organic frameworks for optical applications

• Ultrasonication during layer-by-layer MOF film synthesis improves film quality.
• These MOF films are transparent and more homogenous with reduced surface roughness.
• These MOF films are suited for optical applications, e.g. as coatings and sensors.

The optical and structural quality of thin films of metal-organic frameworks (MOFs) is of utmost importance for most potential applications as sensors and other optical devices. In this work, a dipping robot equipped with an ultrasonic bath has been developed to prepare thin, homogenous surface-mounted MOFs (SURMOFs) with well-defined thicknesses and orientations. SURMOFs of type HKUST-1, prepared with and without ultrasonication, were characterized by means of XRD, SEM, AFM and UV–vis spectroscopy. It was found that the MOF films prepared with ultrasonication are significantly cleaner, more homogenous and have a considerably smaller surface roughness than MOF films prepared without ultrasonication. The higher film quality results in a tremendously improved transparency, making them perfectly suited for optical applications.

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