Gas sensors are indispensable for detecting harmful gases in the environment. The morphology of a gas sensor significantly affects its sensing performance. Among the various morphologies, one-dimensional nanowires (NWs) have numerous advantages, such as high surface area, small dimensions, high charge-carrier concentrations, facile synthesis, high crystallinity, and stability. These excellent properties make NWs promising for gas sensing. Resistive-type metal oxide-based gas sensors are widely used for monitoring various toxic gases and volatile organic compounds. In this tutorial, the synthesis of metal oxide NWs, the fabrication of gas sensors, and their sensing mechanisms are discussed. Different types of NW-based gas sensors, such as single NWs, branched NWs, noble metal-functionalized NWs, heterojunction NWs, self-heating NWs, ultraviolet-activated NWs, core–shell NWs, and electronic-nose-based NWs, are comprehensively presented. Finally, we discuss future directions with regard to the improvement and potential of these NW gas sensors. This tutorial aims to provide an overview of the fundamental principle and state-of-the-art technology, which is useful for researchers and students working in the field of resistive-type NW-based gas sensors.

ZnFe₂O₄ was fabricated by a simple solution-combustion method. The structural, optical and electronic properties are investigated by XRD, TEM, FESEM, UV–vis DRS, PL, FTIR and photocurrent measurements. The photocatalytic activity of the prepared material is studied with regard to the degradation of rhodamine B (Rh B) and Congo red under solar irradiation. The kinetic study showed that the material exhibits zeroth and first order reaction kinetics for the degradation of Rh B and Congo red, respectively. The photocatalytic behaviour of ZnFe₂O₄ was systematically studied as a function of the activation temperature. ZnFe₂O₄ prepared at 500 °C showed the highest activity in degrading Rh B and Congo red. The highest activity of ZnFe₂O₄-500 °C correlates well with the lowest PL intensity, highest photocurrent and lowest particle size.

An overview of the MOF-based gas sensing materials with different electrical transduction principles.

Reduced graphene oxide (rGO) is a reduced form of graphene oxide used extensively in gas sensing applications. On the other hand, in its pristine form, graphene has shortages and is generally utilized in combination with other metal oxides to improve gas sensing capabilities. There are different ways of adding rGO to different metal oxides with various morphologies. This study focuses on rGO-loaded metal oxide nanofiber (NF) synthesized using an electrospinning method. Different amounts of rGO were added to the metal oxide precursors, and after electrospinning, the gas response is enhanced through different sensing mechanisms. This review paper discusses rGO-loaded metal oxide NFs gas sensors.