Photo-response range extension of Z-scheme ZnO/CdS for LED-light-driven photo-active catalyst

Abstract

Zinc oxide (ZnO) photocatalysts are suitable for wastewater treatment via photocatalytic processes. However, they are hindered by fast e− and h+ recombination, a large bandgap, and the need for a high-energy light source for activation. Thus, this study was aimed to synthesize a photocatalyst that operates under a low-energy consumption. We introduced cadmium sulphide (CdS) heterojunction to ZnO photocatalyst, and successfully reducing their bandgap from 3.30 eV to 2.46 eV. This modification allows activation with a 21-Watt light-emitting diode (LED) visible light source. The surface structure characteristics of the ZnO/CdS photocatalyst was analyzed using XRD, HRTEM, FESEM, and N2 adsorption-desorption isotherms. UV-NIR was used for bandgap analysis and the DFT simulation method to compute the atomic properties of the materials. Catalytic evaluation showed that the ZnO/CdS photocatalyst completely degraded the model dye solution (100%) using 0.5 g of Z3C1 (3:1 M ratio) of 100 mg L−1 MB solution at pH 9 within only 90 min. A scavenger test confirmed that the hydroxyl OH• and superoxide •O2− radicals proved were the major active species responsible for degradation process. The reusability of Z3C1 was demonstrated over 4 reaction cycles, proving that CdS significantly enhances visible light absorption by extending the photo-response range and promoting superior formation of e− and h+. This delays their recombination due to the Z-scheme type, making it highly potential for wastewater treatment.