New Modified Sol–Gel Method for the Preparation KNb₃O₈ as a Hydrogen Evolution Photocatalyst in Z-Scheme Overall Water Splitting

The layered potassium niobate, KNb₃O₈, is evident as a photocatalyst for hydrogen production from water splitting under UV light. We hereby reported a new modified sol–gel method for the preparation of potassium niobate photocatalyst. Photocatalytic water splitting has been improved in this work by loading Pt nanoparticles as cocatalyst. The catalysts were characterized by powder X-ray diffraction (XRD), Ultraviolet–Visible spectroscopy (UV–Vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their photocatalytic activities were in (i) an aqueous MeOH, used as sacrificial hole scavengers for hydrogen production and (ii) a new Z-scheme photocatalytic water splitting system where Pt/KNb₃O₈ was used for H₂ evolution and Pt/WO₃ was used for O₂ evolution. The I⁻/IO₃⁻ aqueous solution was used as redox couple for the photocatalytic Z-scheme over all water splitting under UV light irradiation. The photocatalysts were prepared by loading platinum on sol–gel synthesis KNb₃O₈ and commercial WO₃ via impregnation method. We find that, this KNb₃O₈ belonging to a orthorhombic structure with rod-like morphology. The Pt nanoparticles were sufficiently well-dispersed on the surface of photocatalyst, and enhanced photocatalytic properties. Our results show that I⁻ concentration significantly influenced the photocatalytic activity. The combination of Pt/KNb₃O₈ with Pt/WO₃ achieves a high H₂ evolution rate (539 μmol g⁻¹ h⁻¹) and O₂ evolution rate (140 μmol g⁻¹ h⁻¹) in 2 mM NaI solution.