Solid solution ZnW1−xMoxO4 for enhanced photocatalytic H2 evolution

Abstract

Layered ZnWO₄ is a promising photocatalyst; however, its poor light absorption properties limit its practical applications. In this work, Mo-doped ZnWO₄ (ZnW_1−xMo_xO₄) was prepared by a hydrothermal method. X-ray diffraction data for ZnW_1−xMo_xO₄ revealed that the materials retained the layered structure after Mo doping. The synthesized layered ZnW_1−xMo_xO₄ had absorption edges at around 390 nm when x = 0.4. In the presence of Mo, ZnW_1−xMo_xO₄ produced H₂ from an aqueous solution containing Na₂SO₃ and Na₂S as reversible electron donors which was ca. 2.2 times higher than that of ZnWO₄ (607.1 μmol g⁻¹ h⁻¹vs. 271.2 μmol g⁻¹ h⁻¹). This high activity could be attributed to the formation of a trap level after Mo doping, which was confirmed by X-ray photoelectron spectroscopy. In addition, by combining ZnW_1−xMo_xO₄ with CdS to form an n–n heterojunction, an approximately 9.8 times higher activity than that of ZnWO₄ was observed (2658.1 μmol g⁻¹ h⁻¹vs. 271.2 μmol g⁻¹ h⁻¹). This work provides a method for the modification of wide band gap semiconductors, which sheds new light on the future design of high activity photocatalysts.