Effective enhancement on humidity sensing characteristics of sulfonated poly(ether ether ketone) via incorporating a novel bifunctional metal–organic–framework

Recently, sulfonated poly(ether ether ketone) (SPEEK) has been used as the humidity sensing material due to its simple processing, environmental stability, and large humidity responding range. However, intrinsic shortcomings such as large hysteresis and lags in response restrict its practical application. Thus, a novel bifunctional metal–organic–framework, MNS (abbreviation for MIL-101-NH 2 -SO 3 H) was prepared as an inorganic nano-filler to improve sensing properties of humidity sensor based on SPEEK, especially small hysteresis. Humidity sensitive properties of sensors were investigated by measuring the complex impedance spectra of sensors at different relative humidity (RH). The organic-inorganic humidity sensor based on the composite material (SPEEK/MNS-30%) showed the best sensing properties, such as quick response (absorption: 9   s) and small hysteresis (<3% RH, almost eighth of SPEEK sensor). Besides, the mechanism of the enhancement caused by MNS was proposed and proved by investigating the surface structure and microstructure of humidity sensing film via scanning electron microscopy and transmission electron microscopy , respectively. In addition, the equivalent circuit was built up by complex impedance spectra to study the sensing behavior of the composite humidity sensor. The good reproducibility and stability of the humidity sensor fabricated by SPEEK/MNS-30% indicated that it had the potential to be applied for practical humidity detection .