Microstructures and Photodegradation Performance toward Methylene Orange of Sputtering-Assisted Decoration of ZnFe₂O₄ Crystallites onto TiO₂ Nanorods

In this study, TiO₂⁻ZnFe₂O₄ (ZFO) core-shell nanorods with various ZFO crystallite thicknesses were synthesized through sputtering-deposited ZFO thin films onto the surfaces of TiO₂ nanorods. By coupling the ZFO narrow bandgap oxide with TiO₂, an enhanced photodegradation efficiency of methylene orange under irradiation was achieved. Structural analyses revealed that ZFO crystallites fully covered the surfaces of the TiO₂ nanorods. The sputtering-deposited ZFO crystallites on the head region of the composite nanorods were markedly thicker than those covering the lateral region of the composite nanorods. The coverage of ZFO crystallites on the TiO₂ nanorods led to an improved light harvesting, a decrease in the hole⁻electron recombination rate, as well as the enhanced photodegradation activity of the TiO₂⁻ZFO heterostructures under irradiation. The optimized ZFO thickness on the head region of the composite nanorods was approximately 43 nm on average and that at the lateral region of the composite nanorods was 15 nm, which exhibited superior photodegradation ability to methylene orange and retained a stable photodegradation efficiency of approximately 97% after cycling tests. The results herein demonstrate that sputtering deposition of ZFO crystallite with tunable thickness is a promising approach to designing TiO₂⁻ZFO composite nanorods with various ZFO coverage sizes and to adjust their photodegradation ability toward organic dyes.