Superior photocatalytic H₂evolution from Zn vacancy engineered Cu⁺-Doped ZnS@Cu_xS heterostructures

Cation vacancy engineering is an effective strategy to enhance photocatalytic performance, as it introduces new energy states, suppresses photo-corrosion, and improves charge trapping and transfer in sulfide semiconductors. In this study, Zn-vacancy–rich ZnS was synthesized via a one-step hydrothermal method and further modified through Cu⁺ doping and Cu_xS heterojunction formation by cation exchange. Structural and spectroscopic analyses confirmed abundant Zn vacancies as well as successful Cu⁺ doping and Cu_xS formation. The Zn vacancy reduces the band gap and creates trap states, thereby enhancing charge separation efficiency. Additionally, Cu⁺doping controls the vacancy content and regulates the band structure, which improves the reduction ability of the electrons. Furthermore, the Cu_xS heterojunction increases visible light absorption and boosts stability by enhancing charge separation efficiency through the Type–II heterojunction. Under optimized conditions (3 mol% Cu), the photocatalyst achieved a high hydrogen production rate of 20.74 mmol g⁻¹ h⁻¹with excellent stability. This work demonstrates a simple and effective approach to vacancy engineering and highlights its potential for designing efficient photocatalysts for solar-to-hydrogen conversion.