Efficient and durable ZnO core-shell structures for photocatalytic applications in aqueous media

Core-shell nanostructures were synthesized by aerosol assisted chemical vapor deposition method. A ZnO nanorod (ZNR) was the core material, while the shell coating was individually film of Ti, Cu-Zn or Fe oxide. The crystalline phases of the synthesized materials were identified as oxides in the form of wurtzite (ZnO), anatase (TiO2), tenorite (CuO) and hematite (Fe2O3). Only for samples prepared using single Ti and Fe sources, amorphous shells were detected. The photocatalytic performance of all samples was tested by the discoloration of methylene blue. Findings confirmed that bare ZnO nanorods and commercial photocatalyst (Degussa P25) are comparable photocatalysts since 99% of dye discoloration was achieved in 60 min. Additionally, discoloration tests performed with the core-shell nanostructures revealed that the ZNR/TiOx and ZNR/CuO-ZnO samples exhibited more than 93% of discoloration in 60 min. Nevertheless, with samples involving ZNR/Fe2O3 and ZNR/FeOx/TiO2/Fe2O3, a maximum of 33% of dye discoloration was measured. Microstructural changes of the samples before and after the photocatalysis essays were examined. Results showed that the bare ZnO and CuO-ZnO coated nanorods dissolved in the aqueous medium. Conversely, the integrity of the ZnO core was evidenced through the morphological and structural analysis, when single TiOx and multiple FeOx and Fe2O3 layers, were employed. Furthermore, quantitative measurement of Zn solubility was performed in selected samples to confirm dissolution inhibition. Noteworthy, outcomes suggest that the functionality of ZnO when applied in aqueous systems could be assured solely with the developed ZNR/TiOx material.