Room temperature optical gas sensing properties of Na- doped zinc oxide nanoparticles: improving response and recovery time

We report the results of NO₂ gas sensing performance of pure and Na doped (0.1%, 0.2%, and 0.3% w/w) zinc oxide nanoparticles synthesized via aqueous solution growth technique. The structural, morphological, and optical properties of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, UV–Vis spectroscopy, and photoluminescence (PL) spectroscopy. PL and Raman spectral studies indicated that the ZnO nanoparticles possess more vacancies or lattice defects compared to the conventional ZnO nanoparticles (ZNP) prepared through various synthesis techniques. This work focuses on optical gas sensing at normal atmospheric pressure and room temperature to detect the presence of nitrogen dioxide gas. The optical NO₂ gas sensing studies revealed the substantial role of Na doping on the sensing properties of the synthesized samples, with gas concentrations ranging from 500 ppb to 30 ppm. Remarkably, 0.2% w/w Na-doped zinc oxide nanoparticles demonstrated an 84.7% response to 20 ppm NO₂ gas, with a quick response time (τ) of 9 s and a recovery time of approximately 20 s at room temperature and atmospheric pressure. The good sensing response, short response and recovery time, low detection limit and stability exhibited by 0.2% Na-ZnO nanoparticles make them promising candidates for fabricating efficient and reliable NO₂ sensors.