Synergetic microstructure engineering by induced ZB/WZ twin boundaries and S vacancies in a Zn_0.5Cd_0.5S-based S-scheme photocatalyst for highly efficient photocatalytic hydrogen production

Surface-abundant active sites, rapid charge transport and associated prolonged electron lifetime are vital factors that determine efficient photocatalysis. A series of different Zn_0.5Cd_0.5S solid solutions, including single crystalline Zn_0.5Cd_0.5S (ZCS), single crystalline Zn_0.5Cd_0.5S with S vacancies (ZCS-V), twin structured-Zn_0.5Cd_0.5S (T-ZCS) and twin-structure Zn_0.5Cd_0.5S with S vacancies (T-ZCSv) were successfully prepared in the present work by manipulating the conditions of the hydrothermal reaction. Experimental results confirm that the optimized T-ZCSv photocatalyst that possesses a hexagonal wurtzite/zinc blende (WZ/ZB) twin structure and rich-surface S vacancies exhibits an excellent photocatalytic hydrogen production efficiency of approximately 551.74 μmol h⁻¹. The outstanding performance of the optimized T-ZCSv is attributed to the prolonged electron lifetime and effectively facilitated separation and migration of charge carriers. These are provided by the periodically aligned WZ/ZB interfacial homojunctions that form the S-scheme staggered energy band structure across the junction and abundant S vacancies that serve as electron trapping sites in the T-ZCSv. Furthermore, T-ZCSv are uniformly dispersed on 2-methylimidazole zinc salt [zeolitic imidazolate framework-8 (ZIF-8 polyhedron)], which not only could inhibit the aggregation of T-ZCSv but also expose more active sites for photocatalytic-redox reactions. Finally, a possible charge separation and transfer mechanism explaining the optimum activity of the outperforming sample is proposed on the basis of the results obtained from a range of investigation methods [scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy and high-resolution transmission electron microscopy (TEM/HRTEM), X-ray diffraction (XRD) technique, ultraviolet-visible (UV-vis) diffuse reflection spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy]. This study demonstrates the development of a structurally unique Zn_0.5Cd_0.5S (with twin structure and S vacancies) and a Zn_0.5Cd_0.5S-based metal-organic framework (MOF) for photocatalytic applications.