Morphology control and enhanced activity of (Cu-S)_nMOF@ZnS heterostructures for photocatalytic H₂ production

A novel metal-organic framework (MOF), (Cu-S)_nMOF, with a copper-sulfur planar structure was applied to photocatalytic H₂ production application. (Cu-S)_nMOF@ZnS nanocomposite was synthesized using a microwave-assisted hydrothermal approach. The formation of (Cu-S)_nMOF and wurtzite ZnS in the composite nanoparticles was analyzed by X-ray diffraction (XRD), field emission-scanning electron microscopy (FESEM), and high-resolution transmission electron microscope (HRTEM). The electron-hole separation and interfacial charge transfer resistance of (Cu-S)_nMOF@ZnS were evaluated by photocurrent response, electrochemical impedance spectroscopy (EIS), steady-state photoluminescence (PL), and time-resolved photoluminescence (TRPL) analysis. The photocatalytic activity can be tuned by changing the zinc acetate precursor/MOF ratio, reaction time, and reaction temperature. Electron paramagnetic resonance (EPR) study and Zeta potential confirm the presence of S vacancies in the composite nanoparticles. The ultraviolet photoelectron spectroscopy (UPS) and Tauc plots were measured to establish the band structure of the composite photocatalyst. A type-II heterojunction is formed at the interface, leading to improved electron-hole separation efficiency of the (Cu-S)_nMOF@ZnS photocatalyst. The (Cu-S)_nMOF@ZnS photocatalysts exhibit higher photocatalytic H₂ production activity than pristine (Cu-S)_nMOF and ZnS nanoparticles. The optimal (Cu-S)_nMOF@ZnS photocatalyst exhibits an improved H₂ generation rate of 33,912 μmolg^-1·h^-1, which is 6.6 times that of pristine (Cu-S)_nMOF (5138 μmolg^-1·h^-1).