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.

Reduced graphene oxide (rGO) has attracted enormous interest as a promising candidate material for gas detection due to its large specific surface areas. In our work, rGO films were fabricated on a large scale using dip-coating and spin-coating methods for the detection of nitrogen dioxide (NO₂) gas at room temperature. The influence of different test environments on the sensing performance, including the test atmosphere, gas flow and gas pressure was evaluated. The response time of the dip-coating method was 573 s with a long recovery period of 639 s and for the spin-coating method, the response time and recovery time was 386 s and 577 s, respectively. In addition, the spin-coated sensor exhibited high selectivity to NO₂, with the response increasing by more than 20% (for 15 ppm NO₂) as compared with that for HCHO, NH₃, and CH₄. Our results indicated that the spin coating method was more suitable for rGO-based gas sensors with higher performance.