Defects Enriched p-type Zinc Stannate for Selective Detection of ppb-Level NO₂ Gas at Ambient Temperature

In this study, we explore the synthesis and gas-sensing capabilities of zinc stannate (Zn 2 SnO 4 ) in three morphologies─spherical nanoparticles, urchins, and octahedrons─aiming to investigate the influence of morphology on sensing properties. The fabricated devices exhibit a significant resistance decrease upon exposure to NO 2 at room temperature (24 °C), indicating p-type sensing behavior. Among these morphologies, the spherical nanoparticle-based sensor exhibits the highest sensor response of 57% to 6 ppm of NO 2, outperforming urchins and octahedrons by approximately 1.2 and 4.1 times, respectively. This superior performance, with response and recovery times of 6.3 s and 224 s, is attributed to enhanced redox reactions from a larger surface area and a higher proportion of oxygen interstitials. The spherical nanoparticle-based sensor also demonstrates exceptional selectivity for NO 2 over SO 2, CO, NH 3, and CH 4, with a detection limit of 200 ppb. Furthermore, the sensor exhibits excellent reversibility with only 2% variation across 20 consecutive test cycles and demonstrates remarkable long-term stability, with a performance fluctuation of approximately 2.3% over 63 days without significant degradation.