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This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H₂). In particular, 3-dimensional Nb₂O₅/g-C₃N₄ heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb₂O₅ with a low charge carrier recombination rate and a g-C₃N₄ exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb₂O₅ to g-C₃N₄ on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co-catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron-hole pairs is found to increase significantly as compared to that of pure Nb₂O₅ and g-C₃N₄, respectively, with the highest molecular H₂ production of 110 mmol/g·h being obtained for 10 wt % of g-C₃N₄ over Nb₂O₅ as compared with that of g-C₃N₄ (33.46 mmol/g·h) and Nb₂O₅ (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron-hole pairs at the Nb₂O₅/g-C₃N₄ interface through a direct Z-scheme.