In-situ controllable assembly of 3D ZnO-ZnS heterojunction nanotube arrays for enhancing NO2-sensing performance at low energy consumption and sensing mechanism

The ZnO-ZnS composite nanotube arrays were grown in-situ on the ceramic tube substrate via hydrothermal route without any surfactant. ZnS nanoparticles are evenly coated on the surface of ZnO nanotubes to form a large number of nano-heterojunction structures. The response of the sensor is 14.25–10 ppm NO2 at the optimal operating temperature 170 °C. The lowest detection concentration reaches 0.5 ppm at 170 °C. The sensor also shows perfect selectivity, moisture resistance and long-term stability. The composite of ZnO and ZnS significantly increases the response of sensing material, and even achieves the room temperature response to NO2. The excellent NO2 sensing properties of the sensor are attributed to the unique nanotube arrays structure. It provides more active sites, which facilitates gas molecules to adsorb on the surface of the materials. At the same time, the hollow structure of nanotubes is also conducive to gas molecules diffusion. The detailed sensing mechanism analysis is further proved by techniques such as XPS, GC-MS, UV–Vis and Kelvin probe techniques.