Influence of anodization time on Al2O3 nanoporous morphology and optical properties using energy band gap at room temperature

Development of nanoporous structures at room temperature using one-step anodization is well-known as a simple and cost-effective method for various industrial applications. In this study, we fabricated anodized alumina with nanoporous structures using oxalic acid as an electrolyte at an optimum potential voltage of 40 V. To understand the effect of anodization time on the morphology of the resulting nanostructures, and the anodization process was performed at different time durations, t = 40, 80, and 120 min. The results show that the anodization time influences the nanopore size. After comparison of morphologies of the developed nanostructures, we further discussed the material (elemental composition and phase purity) and optical characterization of Al2O3 nanoporous structure in comparison with the previous literature reports. The XRD and FTIR results confirm that the alumina phase dominates the aluminum phase. Our study also showed that Urbach energy (representing disorders associated with the electron transmission to determine the defects in materials via localized states) of the alumina phase is 0.47–0.520 eV, indicating fewer defects in the system. Further, the energy band gaps for the developed nanoporous structures were ∼2.83–2.90 eV (Tauc plot) and ∼2.27–2.31 eV (Absorption Spectrum Fitting). These results emphasize the potential of anodic alumina as a photoelectrode material for solar power-driven applications.