Synthesis and optimization strategies of nanostructured metal oxides for chemiresistive methanol sensors

Thanks to the merits such as high specific surface areas, superior electronic conduction and unique gas diffusion path derived from the nanoscales, the demand for detecting methanol has contributed to the rapid expansion of gas sensors based on metal oxide nanostructures. In this review, the “process-structure-performance” correlations of metal oxide nanostructures utilized in the detection of methanol are analyzed. The sensing mechanisms of nanostructured metal oxides operated at different temperatures for methanol monitoring are first introduced. Subsequently, various synthesis processes (e.g. hydrothermal, sol-gel and electrospinning) utilized to modulate the structure and morphology of metal oxide nanostructures are discussed. Given the limitations that existed in methanol gas sensors, numerous optimization strategies including doping, surface modifications, newly designed structures and morphologies, the self-doping defects are enumerated to dramatically enhance the sensing properties represented by the improvement of sensitivity, the reduction of working temperature, the decrease of detection limit, etc. Additionally, the challenges and future research directions of advanced methanol sensors based on metal oxide nanostructures are proposed. It is ultimately expected that this review will help break the bottleneck of nanostructured metal oxides gas sensors in the field of methanol detection, and further promote the actual application of chemiresistive methanol sensors.