Impact of Annealing on ZrO2 Nanotubes for Photocatalytic Application

This work aims to study the structural, optical, and photocatalytic properties of ZrO2 nanotubes (NTs) that have been synthesized using the electrochemical anodization method. The structural and morphological characteristics of unannealed and annealed (400 degrees C, 500 degrees C, and 700 degrees C) ZrO2 NTs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Details of the structural and morphological results are depicted to clarify the effect of annealing temperature on the NTs. Furthermore, the reflectivity and photoluminescence of ZrO2 NTs were found to depend on the annealing temperature. The resulting bandgap values were 3.1 eV for samples annealed at 400 degrees C and 3.4 eV for samples annealed at 550 and 700 degrees C. Thus, amorphous and annealed ZrO2 NTs were tested in terms of their photocatalytic degradation of Black Amido (BA) dye. Samples annealed at 400 degrees C exhibited 85.4% BA degradation within 270 min compared to 77.5% for samples annealed at 550 degrees C and 70.2% for samples annealed at 700 degrees C. The anodized ZrO2 NTs that were annealed at 400 degrees C showed the coexistence of tetragonal and monoclinic crystalline phases and exhibited the fastest photocatalytic performance against the BA dye. This photocatalytic behavior was correlated to the crystalline phase transformation and the structural defects seen in anodized ZrO2.