In-situ polymerization of metal organic frameworks-derived ZnCo2O4/polypyrrole nanofilm on QCM electrodes for ultra-highly sensitive humidity sensing application

Abstract

A metal organic frameworks (MOFs)-derived ZnCo2O4/polypyrrole (ZnCo2O4/PPy) nanocomposite coated QCM humidity sensor with high performance was demonstrated in this paper. The element composition, morphology and nanostructure of the ZnCo2O4/PPy nanocomposite were characterized by energy dispersive spectroscopy (EDS), FT-IR spectrums, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). All humidity sensing tests of ZnCo2O4/PPy QCM sensor were performed under room temperature environment. The experimental results revealed that the ZnCo2O4/PPy sensor exhibits excellent humidity sensing behavior. Comparing with pure PPy and pure ZnCo2O4 sensor, ZnCo2O4/PPy film coated QCM humidity sensor displays higher sensitivity (58.4 Hz/%RH) and better response/recovery properties (8 s/7 s). Besides, the equivalent circuit elements parameters of ZnCo2O4/PPy coated QCM sensor at various RH environments were determined by the modified Butterworth-Van-Dyke (BVD) equivalent circuit model. And the adsorption kinetics of water molecules was investigated by bimodal exponential kinetic adsorption model.