4.1. Materials Synthesis

The α-Fe₂O₃ nanorod template was synthesized through a hydrothermal method. The 3.028 g of iron chloride hexahydrate (FeCl₃⋅6H₂O) and 0.72 g of urea (CO(NH₂)₂) were dissolved into deionized water to form a 60 mL mixture solution as a reaction solution. The F-doped tin oxide (FTO) substrates were perpendicularly leant in the aforementioned solution, and then tightly sealed and maintained at 100 °C for 24 h in an electric oven. Finally, the products were annealed at 500 °C for 30 min in the muffle furnace. The detailed hydrothermal reaction parameters have also been described elsewhere [3]. The Fe₂O₃ nanorod template was coated with a ZnO seed layer via radio-frequency sputtering at room temperature with a ZnO ceramic target. The sputtering process was conducted in an Ar/O₂ mixed atmosphere with an Ar/O₂ ratio of 4/1. The sputtering working pressure was 20 mTorr and the sputtering power was ZnO 90 W in this study [10]. The sputtering duration of the ZnO seed layer is 60 min. After that, the ZnO seed layer-coated Fe₂O₃ nanorod template on FTO substrates was perpendicularly suspended in a homogeneous mixture solution containing 100 mL of deionized water, 0.7 g of Hexamethylenetetramine (C₆H₁₂N₄), and 1.4869 g of Zinc Nitrate Hexahydrate (Zn(NO₃)₂). The hydrothermal reaction was conducted at 95 °C for 1.5 h to synthesize brush-like Fe₂O₃-ZnO samples.