Effect of annealing temperature on the characteristic of reduced highly ordered TiO₂nanotube arrays and their CO gas-sensing performance

A study on the effect of temperature on the reduced highly ordered TiO₂nanotube arrays (reduced-HOTNAs) and their CO gas-sensing performance is reported. The reduced-HOTNAs were prepared by anodizing method followed by annealing in the presence of urea at various temperatures (i.e. 450, 500, 550, 600 and 700 °C) under N₂atmosphere. The reduced-HOTNAs were characterized by FTIR, FE-SEM, XRD, UV-Vis DRS, Raman spectroscopy and photoelectrochemical techniques. The sensing performance of the reduced-HOTNAs was assessed against CO gas in air mixture. The results show that the reduced-HOTNAs annealed at 450 °C (reduced- HOTNAs-450) is a material with the most significant improvement in sensitivity to detect CO compared with other reduced-HOTNAs. The reduced-HOTNAs-450 exhibits best sensing performance at a relatively low CO concentration in the range of 2-25 ppm at 300 °C. Findings of this study indicate that improvement of the reduced-HOTNAs-450 sensitivity might be attributed to the presence of Ti3+/oxygen vacancy defect and the formation of more active sites on TiO₂surface, making the reduced-HOTNAs-450 a promising active material for CO gas sensor application.