By a mild and straightforward synthetic protocol in aqueous solution and without surfactants, hierarchical Cu₂O nanospheres were grown on preformed In₂O₃ nanostructures, varying the ratio In : Cu (2.5, 0.5). Accordingly, two different binary compounds In₂O₃‐Cu₂O were prepared and afterwards they were integrated with TiO₂ NPs. The ternary composites having a loading of 2.0, 5.0 and 10.0 wt.% respectively of binary In₂O₃‐Cu₂O, were tested as photocatalysts in the solar‐driven production of hydrogen from water, using as sacrificial agents alcohols derived from the biomass. Satisfyingly, the rate of H₂ evolution (20.5 mmol/g h) resulted two orders of magnitude higher respect to bare TiO₂ (0.2 mmol/g h). Electrochemical impedance spectroscopy and photoluminescence measurements revealed the formation of a tight heterojunction between In₂O₃ and Cu₂O, which is responsible for the improved charge carrier density and transfer and for the diminished electron‐hole recombination.

In this work, bare copper oxide-based catalysts were synthesized and evaluated for their dual (photo)catalytic activity in two model reactions: hydrogen generation via formic acid decomposition (FAD) and the photocatalytic hydroxylation of benzene to phenol. Catalysts were prepared from copper nitrate and copper acetate precursors and calcined for either 10 min or 2 h. Their structural and surface properties were characterized by wide-angle X-ray diffraction (WAXD), Raman spectroscopy, and BET surface area analysis. FAD was conducted under mild thermal conditions and monitored via ¹H NMR spectroscopy. At the same time, benzene hydroxylation was performed under UV irradiation and analyzed by gas chromatography (GC) and high-performance liquid chromatography (HPLC). All synthesized catalysts outperformed commercial CuO in the selective oxidation of benzene. The nitrate-derived sample calcined for 10 min (NCuO 10 min) achieved the best performance, with a phenol yield of ~10% and a selectivity of up to 19%, attributed to improved surface properties and the presence of Cu(I) domains, as indicated by Raman spectroscopy. For FAD, complete conversion of formic acid was achieved at low temperatures, with selective H₂ and CO₂ evolution and complete suppression of CO, even under short reaction times and low catalyst loadings. These results demonstrate the potential of nitrate-derived CuO catalysts as versatile, dual-function materials for sustainable applications in selective aromatic oxidation and low-temperature hydrogen generation, without the need for noble metals or harsh conditions.