Enhancing the gas detection response of biodegradable NO2 sensors by creating on their surface oxygen-vacancies/zinc-interstitial defects

Abstract

In this research, flexible and biodegradable NO2 gas sensors were fabricated using dried mango peel, graphene, ZnO and carbon nanotubes. We fabricated two sensors, the first one used as sensitizing material ZnO with oxygen vacancy defects (Vox) and the second one employed ZnO with zinc interstitials (Znix) defects. The average gas response values (ΔR/R0 value at 100 ppm and RH=35%) were 0.16 and 0.21 for the gas sensors fabricated with Vox and Znix, respectively. Moreover, the response/recovery times were 13.9/213.2 s and 11.4/145.5 s for the sensors fabricated with Vox and Znix, respectively. Interestingly, a reference sensor made without ZnO had 10–14 lower gas response values and 1.41 times higher response times than the sensors made with ZnO. This means that adding defective ZnO on the sensors’ surface was key to enhance the detection of NO2. Additionally, the performance of the sensors was studied for relative humidities (RH) in the range of 35–82% and found that the response times decreased from 11.4 to 13.9 s to 10.8–12.5 s after raising the RH from 35% to 57%. In general, the lowest response times were obtained in the sensors fabricated with Znix. Controlling the response/recovery times with ZnO-defects paves the way to improve the state-of-the-art ZnO based sensors.