Heterogeneous Metal Oxide-Graphene Thorn-Bush Single Fiber as Freestanding Chemiresistor.

The development of freestanding fiber-type chemiresistor, having high integration ability with various portable electronics including smart clothing system, is highly demanding for the next-generation wearable sensing platform. However, critical challenges stemming from irreversible chemical sensing kinetics and weak reliability of the freestanding fiber-type chemiresistor hinder their practical use. In this work, for the first time, we report on potential suitability of the freestanding and ultraporous reduced graphene oxide fiber functionalized with WO3 nanorods (porous WO3 NRs-RGO composite fiber) as a sensitive nitrogen dioxide (NO2) detector. By employing tunicate cellulose nanofiber (TCNF), which is a unique animal-type cellulose, the numerous mesopores are formed on wet-spun TCNF-GO composite fiber, unlike bare GO fiber with dense surface structure. More interestingly, due to the superior wettability of TCNF, the aqueous tungsten precursor is uniformly adsorbed on ultraporous TCNF-GO fiber and subsequent heat treatment results in the thermal reduction of TCNF-GO fiber and hierarchical growth of WO3 NRs perpendicular to the porous RGO fiber (porous WO3 NRs-RGO fiber). The freestanding porous WO3 NRs-RGO fiber shows a notable response to 1 ppm of NO2. Furthermore, we successfully demonstrate reversible NO2 sensing characteristics of the porous WO3 NRs-RGO fiber, which is integrated on a wrist-type wearable sensing devices.