Novel highly sensitive QCM humidity sensor with low hysteresis based on graphene oxide (GO)/poly(ethyleneimine) layered film

In this work, a novel graphene oxide (GO)/Poly(ethyleneimine) (PEI) layered film was designed and prepared on quartz crystal microbalance (QCM) for humidity detection through a feasible spray process at room temperature. The morphological and chemical properties of GO/PEI layered film were examined by means of field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR), and Raman spectroscopy. The effect of GO solution concentration on humidity-sensing characteristics was investigated and an optimized QCM humidity sensor was obtained. An intriguing phenomenon was observed that a three-dimension structure of GO sheets was formed due to the redissolution effect at the interface between PEI and GO layers. Results showed that a layered film QCM sensor exhibited superior humidity sensing properties than a pure GO film or a PEI one including high response, short response/recovery time, small humidity hysteresis (less than 1%RH), excellent repeatability, selectivity and long-term stability. Moreover, the humidity features of sensors were also researched via the method of impedance analysis. Lastly, a convincing sensing mechanism model was established to interpret the enhanced humidity-sensing performance of layered film sensors. The results demonstrated the potential application of GO/PEI layered films to humidity sensors.