Geometry-Induced Light Trapping in Hollow ZnO Nanostructures for Enhanced Photocatalysis

Abstract ZnO nanostructures with nanoscale confined geometries were fabricated within anodic aluminum oxide (AAO) nanochannels on transparent substrates via atomic layer deposition (ALD). By tuning the ALD cycle number, conformal ZnO layers with thicknesses of 20 and 40 nm were deposited within 70 nm AAO nanopores, resulting in partially open and fully filled nanochannel architectures, respectively. SEM, TEM, and XPS analyses collectively indicated conformal ZnO growth within the AAO nanochannels and demonstrated the structural control achievable through ALD deposition. UV–vis spectroscopy revealed reduced UV transmittance in AAO-assisted structures, suggesting enhanced optical confinement compared to planar ZnO films. Photocatalytic degradation of Methylene Blue test demonstrated improved activity for the ZnO/AAO nanochannel structure, with the ZA-20 sample exhibiting the highest performance. The pseudo-first-order reaction rate constant of ZA-20 was approximately 1.74 times higher than that of planar ZnO under identical UV irradiation conditions. These results indicate a correlation between nanochannel geometry, optical response, and photocatalytic performance, highlighting the potential of AAO-assisted ZnO nanoarchitectures for transparent photocatalytic coating applications.