Influence of pH on Room-Temperature Synthesis of Zinc Oxide Nanoparticles for Flexible Gas Sensor Applications

Abstract

This research contributes to work on synthesizing zinc oxide nanoparticles (ZnO NPs) at room temperature (RT) and their utilization in flexible gas sensors. RT ZnO NP synthesis with a basicity solution (pH ≈ 13) demonstrates an efficient method for synthesizing well-crystalline ZnO NPs (RT.pH13) comparable to those synthesized by the hydrothermal method (hyd.C). The RT.pH13 achieved a high thermal stability with minimal organic reside impurities (~4.2 wt%), 30–80 nm particle size distribution, and a specific surface area (14 m2 g−1). The synthesized pre- and post-calcinated RT.pH13 NPs were then incorporated into flexible sensors for gas sensing applications at ambient conditions (RT and relative humidity of 30–50%). The pre-calcinated ZnO-based sensor (RT.pH13) demonstrated superior sensitivity to styrene and acetic acid and lower sensitivity to dimethyl-6-octenal. The calcinated ZnO-based sensor (RT.pH13.C) exhibited lower sensitivity to styrene and acetic acid, but heightened sensitivity to benzene, acetone, and ethanol. This suggests a correlation between sensitivity and structural transformations following calcination. The investigation of the sensing mechanisms highlighted the role of surface properties in the sensors’ affinity for specific gas molecules and temperature and humidity variations. The study further explored the sensors’ mechanical flexibility, which is crucial for flexible Internet of Things (IoT) applications.