Switchable metal-organic frameworks (MOFs) showing pronounced and stepwise volume changes as a response toward external stimuli such as partial pressure changes were integrated into electron conductive composites to generate novel threshold sensors with pronounced resistivity changes when approaching a critical partial pressure. Two "gate pressure" MOFs (DUT-8(Ni), DUT = Dresden University of Technology, and ELM-11, ELM = Elastic Layer-structured MOF) and one "breathing" MOF (MIL-53(Al), MIL = Material Institute Lavoisier) are shown to cover a wide range of detectable gas concentrations (∼20-80%) using this concept. The highest resistance change is observed for composites containing a percolating carbon nanoparticle network (slightly above the percolation threshold concentration). The volume change of the MOF particles disrupts the percolating network, resulting in a colossal resistance change up to 7500%. Repeated threshold detection is particularly feasible using MIL-53(Al) due to its high mechanical and chemical stability, even enabling application of the composite sensor concept in ambient environment for the detection of volatile organic compounds at high concentration levels.

Chemiresistive threshold sensor films based on the switchable metal−organic framework (MOF) MIL-53(Al) (MIL = Mateŕiaux de l'Institut Lavoisier) and conductive carbon additives were developed, characterized and successfully applied for selective detection of CO 2 in mixtures with methane at high pressure (up to 25 bar). Two transitions of the crystal structure, from the lp (large pore) form to the np (narrow pore) form at CO 2 partial pressure below 0.5 bar and back to the lp form at ca. 6 bar, also known as "breathing", result in two detectable stepwise resistance changes of sensor film, if CO 2 is present in the mixture with methane. The sensor shows a rapid response of the specific resistance (response time ca. 25 s), which directly correlates to the expected structural change of the switchable MOF. Two films containing carbon or carbon nanotubes as conductive component were compared regarding the influence of the additive particles geometry on sensing performance, showing benefits of the isotropic particle shape. Cyclic sensing measurements proved the durability of the composites.

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The force exerted by flexible metal–organic framework through expansion was experimentally evaluated for MIL-53(Al).