Van der Waals Heterostructured MOF-on-MOF Thin Films: Cascading Functionality to Realize Advanced Chemiresistive Sensing.

Heterostructured metal-organic framework (MOF)-on-MOF thin films have the potential to cascade the various properties of different MOF layers in a sequence to produce functions that cannot be achieved by single MOF layers. An integration method that relies on van der Waals interactions, and which overcomes the lattice-matching limits of reported methods, has been developed. The method deposits molecular sieving Cu-TCPP (TCPP=5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) layers onto semiconductive Cu-HHTP (HHTP=2,3,6,7,10,11-hexahydrotriphenylene) layers to obtain highly oriented MOF-on-MOF thin films. For the first time, the properties in different MOF layers were cascaded in sequence to synergistically produce an enhanced device function. Cu-TCPP-on-Cu-HHTP demonstrated excellent selectivity and the highest response to benzene of the reported recoverable chemiresistive sensing materials that are active at room temperature. This method allows integration of MOFs with cascading properties into advanced functional materials.