Covalent organic framework loaded with poly(ionic liquid) for the construction of fast-response humidity sensors with applications in contactless sensing

Covalent organic frameworks (COFs) are novel two dimensional materials with wide application potential in gas adsorption and separation, energy storage and conversion, chemical and biosensors, etc. Herein, COF loaded with poly(ionic liquid) (PIL) was prepared and employed to fabricate a humidity sensor. Specifically, the COF was obtained by interfacial polymerization of tris(4-formylphenyl) amine with 1,3,5-triformylbenzene, and loaded with the PIL via in-situ polymerization of 1-butyl-3-vinylimidazolium tetrafluoroborate under UV irradiation. The PIL@COF sensor exhibited very quick response (t 90% of 2   s for both adsorption and desorption), small hysteresis (relative humidity (RH) of 2%), relatively high sensitivity (impedance change for over one order of magnitude between 11% and 98%RH), high repeatability and good long-term stability. Large specific area of the COF with few polar groups and high content of ionic groups of PIL contributed to the high performance of the sensor. The PIL@COF sensor successfully realized contactless sensing of breath rate and speech recognition, non-contact generation of Morse code and contactless human-machine interactions. The work provides references for the application of COFs in advanced sensors.