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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. [ABSTRACT FROM AUTHOR]