Synthesis of KNbO₃/g-C₃N₄ composite and its new application in photocatalytic H₂ generation under visible light irradiation

High-performance KNbO₃/g-C₃N₄ composite was prepared via a feasible method and first applied in photocatalytic H₂ production from water–methanol solution under irradiation of visible light. The structure and optical property of the synthesized composite were investigated by various techniques, including XRD, XPS, FT-IR, TEM, SEM, DRS, PL, and an electrochemical method. Results indicated that the combining of KNbO₃ with g-C₃N₄ did not affect the optical absorption. However, strong interaction between the two semiconductors was observed, which promotes the fabrication of a heterojunction structure and subsequently improves the separation of photogenerated electrons and holes. Hence, KNbO₃/g-C₃N₄ photocatalyst displayed obviously higher photoactivity than pristine g-C₃N₄. The photocatalytic hydrogen production rate for the optimal KNbO₃/g-C₃N₄ composite (7.4 wt% KNbO₃/g-C₃N₄) is 180 μmol g_cat⁻¹ h⁻¹, which is about 3.0 times that of pristine g-C₃N₄. Cycling tests further proved that KNbO₃/g-C₃N₄ showed good photocatalytic stability. Additionally, the effect of hole sacrificial agent on the photocatalytic activity was also investigated. The KNbO₃/g-C₃N₄ sample showed better performance in the presence of methanol than triethanolamine or EDTA-Na.