ZnO-Co3O4 heterostructure electrospun nanofibers modified with poly(sodium 4-styrenesulfonate): Evaluation of humidity sensing properties

Nanostructured metal oxide semiconductors (MOS) based chemoresistive sensors play an important role in designing handheld, portable and cost-effective sensing systems for the detection of various target analytes. Herein, one-dimensional ZnO-Co3O4 heterostructure nanofibers (NFZCo) were successfully fabricated via electrospinning technique followed by a high-temperature treatment. The heterostructured nanofibers were fully characterized by scanning and transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photo-electron spectroscopy. Using poly (sodium 4-styrenesulfonate) (PSS), a strong anionic polyelectrolyte, to modify the NFZCo surface, a hybrid material (NFZCo-PSS) was prepared, which worked as a humidity sensor through a cost-effective approach. The humidity sensing properties of the hybrid nanomaterial were investigated by exposing it to a wide relative humidity range of 25–75%. The NFZCo-PSS modified electrode exhibited a fast and large response in terms of electrical resistance as the humidity was varied at room temperature. Moreover, the response time for the humidification process was determined as less than 5 s. In general, the sensing performance of the hybrid platform was greatly superior than that of pure NFZCo. Moreover, the humidity sensing mechanism was ascribed to the synergistic effect of the nanofibers morphology and PSS toward water molecules. This work highlights that the hybrid NFZCo-PSS nanofibers can be used as active sensing nanostructures for humidity sensors application.