Highly Sensitive, Selective, Flexible and Scalable Room-Temperature NO₂ Gas Sensor Based on Hollow SnO₂/ZnO...

Semiconducting metal oxides can detect low concentrations of NO₂ and other toxic gases, which have been widely investigated in the field of gas sensors. However, most studies on the gas sensing properties of these materials are carried out at high temperatures. In this work, Hollow SnO₂ nanofibers were successfully synthesized by electrospinning and calcination, followed by surface modification using ZnO to improve the sensitivity of the SnO₂ nanofibers sensor to NO₂ gas. The gas sensing behavior of SnO₂/ZnO sensors was then investigated at room temperature (~20 °C). The results showed that SnO₂/ZnO nanocomposites exhibited high sensitivity and selectivity to 0.5 ppm of NO₂ gas with a response value of 336%, which was much higher than that of pure SnO₂ (13%). In addition to the increase in the specific surface area of SnO₂/ZnO-3 compared with pure SnO₂, it also had a positive impact on the detection sensitivity. This increase was attributed to the heterojunction effect and the selective NO₂ physisorption sensing mechanism of SnO₂/ZnO nanocomposites. In addition, patterned electrodes of silver paste were printed on different flexible substrates, such as paper, polyethylene terephthalate and polydimethylsiloxane using a facile screen-printing process. Silver electrodes were integrated with SnO₂/ZnO into a flexible wearable sensor array, which could detect 0.1 ppm NO₂ gas after 10,000 bending cycles. The findings of this study therefore open a general approach for the fabrication of flexible devices for gas detection applications.