Controlled growth of ZnO nanorod arrays via wet chemical route for NO2 gas sensor applications

•Wet chemical route for the synthesis of ZnO nanorod with a controlled morphology.•Inter-rod space distance between nanorod plays vital role in gas sensing properties.•ZNAs gas sensor detect NO2 at low concentration (100ppm) with sensitivity ∼3100%. Metal oxide gas sensors are promising devices that are widely used to detect various gases at moderate temperatures. In this study, nitrogen di-oxide (NO2) sensors were fabricated using zinc oxide (ZnO) nanorod arrays. ZnO nanorod arrays (ZNAs) with various rod lengths were deposited using a wet chemical route with zinc acetate as a precursor. The structural and surface morphological properties of the ZNAs were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD patterns showed ZNAs with wurtzite crystal structures that were preferentially oriented in the (002) direction. The intensity of the (002) plane was found to vary with the length of the nanorods. FESEM micrographs show that the ZNAs had a vertical alignment perpendicular to the substrate, and the diameter and length of the nanorods increased as the nanorod deposition time was increased. The gas sensing performance was studied as a function of the nanorod length, operating temperature, time and gas concentration. The length and inter-rod space was observed to play a crucial role in determining the gas sensing performance of the devices. ZNA gas sensors deposited for 9h and operating at a temperature of 175°C were able to detect NO2 at a concentration of 100ppm with a high sensitivity of 3100%.