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.