Photo-deposition of Cu2O on Pre-Annealed ZnO Nanorods Yields pn-Heterojunctions with Enhanced Photocatalytic Activity

Abstract

Copper-zinc oxide p-n heterojunctions are promising visible-light-active photocatalysts because their intrinsic bandgaps and band alignment facilitates efficient charge separation. However, achieving controlled deposition of copper oxide nanoparticles on ZnO nanorods remains challenging, particularly in forming well-defined interfaces. Here, we report a UVassisted photodeposition method using [Cu(EDTA)]²⁺ complexes to predominantly form Cu₂O nanoparticles on sea-urchinlike ZnO nanorods that either were used as-prepared or subjected to systematic post-heating treatments. The structural, chemical, and electronic properties of the resulting heterojunctions were characterized by X-ray diffraction, electron microscopy, photoelectron and photoluminescence spectroscopy, while phenol photodegradation products were quantified by HPLC. In contrast to as-prepared ZnO nanorods, annealing treatment prior to Cu₂O deposition produces well-developed Cu₂O-ZnO interfaces, yielding p-n heterojunction nanostructures with enhanced photocatalytic degradation of phenol under UVA illumination. Our results indicate improved interfacial charge transfer, attributed to reduced lattice defects and removal of surface contaminants through annealing. These findings demonstrate that substrate surface preparation combined with atom-by-atom photodeposition of chelated copper complexes provides a straightforward route for optimizing heterojunction catalysts with improved interfacial properties and enhanced photocatalytic activity.