Hydrothermal synthesis of NO2 gas-sensitive and hydrophobic zinc oxide thin films.

NO₂ gas-sensitive and hydrophobic zinc oxide (ZnO) thin films were synthesized through a simple, economical and eco-friendly hydrothermal route. The synthesized material of varying precursor concentrations was deposited on a non-conducting glass substrate. The precursor concentration can tune the morphology of ZnO and, subsequently, sensitivity towards NO₂ gas under study. Once the material gets synthesized, it was annealed at 450 °C and characterized with advanced techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Visible spectroscopy, photoluminescence and water contact angle measurements which ensures the synthesis of material and reveals morphology and other characteristics of the material. The XRD patterns explore the crystallinity as a revealed the hexagonal wurtzite crystal structure. SEM image analysis reveals that with an increase in precursor concentration the size of the ZnO rod also gets increased. The highest gas response (%) = 557.62% is observed at an operating temperature of 200 °C for NO₂ gas at 100 ppm. The response and recovery times are 11.3 s and 126.9 s, respectively, for the optimized sample. Also, the contact angle analysis reveals that hydrophobicity increases with increase in the concentration of precursor. [ABSTRACT FROM AUTHOR]