ZNO coating on kevlar™ fabrics by hydrothermal method and investigation of gas sensor properties

Owing to their nanostructure morphology, flexibility and high thermal resistance, Kevlar fabric substrates are an ideal candidate for obtaining flexible gas sensors for particularly new-generation wearable technologies. The morphology of the surface of the substrate where the target gas comes into contact directly affects the important features of the sensor such as detection limit, selectivity, and response. Here, a practical method for improving the performance of flexible gas sensors based on Zinc Oxide/Kevlar is proposed, which involves adjusting the morphology of Zinc Oxide. Zinc Oxide based gas sensing layers were deposited on Kevlar fabric substrates by a two-stage method. Firstly, a seed layer was produced on Kevlar using the ultrasonic bath method, with five different seed layer processing times ranging from 1 minute to 20 minutes. In the nucleation step, then, all nanostructured layers were deposited by hydrothermal method with constant parameters and under the same experimental conditions. As the seeding time was increased, the nanorods (1 Dimensional) formed on the surface became flakes (2 Dimensional), leading to a considerable improvement in ammonia gas sensing properties. The sensor with a 5-minutes seeding time showed a sensitivity of 49 percent at an optimal operating temperature of 190 °C, while the sensor produced in 20 minutes showed the best response performance with 169 percent at 130 °C for 50 ppm ammonia gas. The increase in seeding time not only reduced the operating temperature of the gas sensor through the conversion from 1 Dimensional nanostructure to 2 Dimensional, but also significantly increased the sensor response. Under constant hydrothermal method conditions and solution concentration, the density per unit area increases. However, after 10 minutes of seeding, the length of nanorods shortens and turn into a rod-flake hybrid morphology. Having set that a superior sensor performance is demonstrated for the investigated samples. The obtained results also showed that flexible Kevlar fabric could be a feasible and interesting substrate for nanostructured Zinc Oxide-based ammonia gas sensors.