Gas sensors based on metal oxide nanoparticles and their application for environmentally hazardous gases detection a mini-review

Hazardous gases have adverse effects on living organisms and the environment. They can beclassified into two categories, i.e. toxic gases (e.g. H2S, SO2, CO, NO2, NO and NH3) and greenhousegases (e.g. N2O, CH4 and CO2). Moreover, their presence in confined areas may lead to fireaccidents, cause serious health problems or even death. Therefore, monitoring of these substanceswith gas sensors allows assessing the quality of the atmosphere, helps avoiding accidents and saveslives. Metal oxide semiconductor gas sensors (MOS) are one of the most popular choices for theseapplications owing to their numerous advantages, i.e. high sensitivity, long lifetime and shortresponse time. However, these devices have their limitations as well. They exhibit baseline drift,sensor poisoning and poor selectivity. Although much has been done in order to deal with thoseproblems, the improvement of MOS sensors continues to attract researchers attention.The strict control of gas sensing materials preparation is one of the approaches that helps to improveMOS sensors performance. Nanomaterials have been found to be more suitable candidates for gasdetection than materials designed at microscale. Moreover, it was found that the regular and orderedmorphology of metal oxide nanostructures, their loading with noble metals, or the formation ofheterojunctionscan exert additional influence on the properties of these nanostructures andimprove their gas sensing performance, which will be described in the following sections of thispaper. Following a discussion of the operation principle of MOS sensors, a comprehensive review ofthe synthesis and application of metal oxide nanoparticles in the construction of the MOS sensorsdedicated for environmentally hazardous gases is presented. The paper discusses also present issuesand future research directions concerning application of nanotechnology for gas sensing.