Effect of anodization voltage on NO2 gas sensing performance of TiO2 and Ag-TiO2 nanotube arrays

The effects of anodization voltages (50 V and 80 V) on the morphological properties of TiO2 nanotube arrays and their NO2 gas sensing performance are investigated. The thin films are synthesized using the electrochemical anodization method and characterized via energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM) and scanning electron microscopy (SEM). The results demonstrated that the nanotubes' length, diameter, and surface roughness are significantly influenced by the anodization voltage, where higher voltage (80 V) led to increase dimensions. Sensing tests revealed that Ag-doping significantly enhances sensitivity compared to pure TiO2 nanotubes. The gas sensing mechanism confirmed that NO2 acts as an oxidizing gas, leading to an increase in the electrical resistance of the n-type TiO2 nanotubes. The maximum sensitivity is achieved at an optimum operating temperature of 200 °C. Furthermore, the Ag-TiO2 sensor exhibited improved response and recovery times, making it a highly efficient candidate for detecting NO2 gas in environmental monitoring applications.