Impact of surface treatments on the photocatalytic performance of anodic aluminum oxide templates

Nanostructured materials receive great interest nowadays due to their unique properties, increased surface areas, and superior performances with associated reduced material usage. However, directly nanostructuring functional materials themselves can be technologically challenging. Hence, nanostructured substrates such as anodic aluminum oxide (AAO) can serve as templates for depositing active materials. The templates' chemical stability is crucial for accurately assessing functional materials. Since AAO structures incorporate electrolyte ions during anodization, their chemical stability is influenced by the subsequent processing after anodization. This work investigates the effect of various post-anodization modifications on the surface chemistry and photocatalytic performance of bare AAO structures. Treatments with H₂O₂ or H₃PO₄ can stabilize the photocatalytic performance of the AAO templates over consecutive measurements. XPS measurements indicate that such stabilization results from AAO surface chemistry alterations. Further, we explore the functionalization of these modified AAO templates with photocatalysts by atomic layer deposition. The photocatalytic performance of TiO₂ as a chemically stable photocatalyst is not affected by the templates' post-anodization treatment. In contrast, the performance of templates functionalized with Fe₂O₃ as an inherent chemically instable photocatalyst depends on the template stability. This work highlights the importance of chemically stable template materials for exploring the properties of new functional materials.