Three-dimensional nano-architecture of copper sulfide/nitrogen-doped titanium dioxide with dual heterojunction for efficient photocatalytic hydrogen generation

A heterojunction in the semiconductor is thought to increase the transfer and separation of photoinduced charge carriers. However, morphology engineering is pivotal for achieving intimate contact between two photocatalysts for efficient charge-carrier transfer. In this work, a simple co-precipitation method yields intimate contact between CuS and N-TiO₂ while maintaining the three-dimensional nanosphere morphology. The narrow band gap in the visible-light region (2.59–2.91 eV) is also observed. The intimate contact in CuS/N-TiO₂ results in a type-II mechanism. Additionally, the plasmonic feature is attributed to the formation of Cu species in the composite, as confirmed by their presence in the Cu 2p core-level spectra and the observed absorption enhancement at 500 nm. Integrating a type-II heterojunction and a Schottky junction in CuS/N-TiO₂ enables fast transfer and separation of photoexcited electron-hole pairs and reduces recombination. Consequently, the H₂ photogeneration rate is improved, with the highest rate of 6248 µmol/g achieved with 0.2CuS/N-TiO₂ as the photocatalyst. Besides, the durability test confirms that 0.2CuS/N-TiO₂ maintains good stability throughout three photocatalytic H₂ generation cycles. This finding implies that good stability of 0.2CuS/N-TiO₂ is an essential factor for scaling up H₂ generation to address energy issues. This direction provides insight into the morphological engineering of dual photocatalysts.