Delafossite (CuFeO2) thin films were hydrothermally synthesized on fluorine-doped tin oxide substrates by using CuFeO2-powder-based seed layers; the photocatalytic properties of these thin films were then investigated. Annealing at 300 °C before hydrothermal reactions yielded thermodynamically stable CuFeO2 islands, which were crucial for strong adhesion of hydrothermal CuFeO2 films. Pure hydrothermal CuFeO2 films were obtained when more than 10 seed layers were used. The proportions of defective Cu2+Cu+ and VO2+ decreased greatly to approximately 29% and 9%, respectively, after hydrothermal reactions, indicating that the fabricated films were predominantly CuFeO2. The energy band diagram of the CuFeO2 films supported their potential for application in photodegradation and photoelectrochemical water splitting. Samples fabricated using 20 seed layers exhibited the highest photodecomposition of methylene blue and Rhodamine B solutions under visible light irradiation. The maximum applied bias photon-to-current conversion efficiency was observed at a bias of −0.5 V, and a cycling study revealed a reliable photocurrent. These photocatalytic properties were attributable to excellent crystallinity, low photoluminescence emission signals, and high electrochemical surface area, all of which contributed to the smooth transport of photoinduced electron−hole pairs to the sample surfaces, thus effectively inducing photocatalysis.
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