A comparative study of capacitive humidity sensor based on keratin film, keratin/graphene oxide, and keratin/carbon fibers

In this paper, we present a comparative study of humidity sensing characteristics of three novel sensing materials, keratin wool as matrix and its composites (keratin/1% graphene oxide, keratin/1% carbon fibers). The composite films have been prepared by a simple solution mixing method. The morphology and structure of the obtained materials were characterized by a scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), and X-ray diffraction (XRD) and were comparatively analyzed. The humidity sensing properties of the fabricated sensors were examined in a wide relative humidity range of 16 %-92 %RH with various test frequencies at room temperature. The experimental results proved that the capacitance of the fabricated sensors increases with the change in relative humidity in the range 16 %-92 % RH. Compared with keratin matrix-based humidity and keratin/1% GO-based humidity, the keratin/1% CF composite-based humidity sensor exhibited a high degree of sensitivity in the order of 633.12 pF/%RH, low hysteresis value and fast response/recovery times. In addition, the sensing mechanism of the humidity sensors was investigated using complex impedance spectroscopy. It was found that the ionic conductivity behavior is generated more easily in keratin/1%CF than in keratin/1%GO and keratin matrix-based humidity sensors. This research revealed that the incorporation of carbon fibers into keratin matrix engenders a new functional composite for the construction of ultra-high sensitivity humidity sensors for various applications. (c) 2021 Elsevier B.V. All rights reserved.