Bandgap engineering of NiWO4/CdS solid Z-scheme system via an ion-exchange reaction

Energy band alignment is essential for efficient charge transfer and solar light utilization in the solid Z-scheme system (SZSS). Here, we propose a strategy to fabricate the NiWO₄/CdS composition as SZSS with an additional feature of a tunable bandgap via an ion-exchange reaction between the NiWO₄ precursor and Cd²⁺/S^2–, which is confirmed with SEM-EDS and Raman spectroscopy. UV–vis DRS and photoluminescence spectrometry determine the bandgap structures. Photosystem II is constructed from NiWO₄, while the structure of photosystem I (PSI) depends on the S content in the composition. As the S content increases from 0 to 45 at%, the bandgap decreases from 2.62 to 1.86 eV for PSI. Moreover, the photoluminescence spectra and photocatalytic H₂ generation experiments demonstrate that the introduction of S provides the proper band alignment for efficient charge transfer and H₂ generation. Bandgap engineering in SZSS by adjusting the S content in the NiWO₄/CdS composition can be also extended to other metal tungstate and metal sulfide composites (MWO₄/MS).