Boosting charge carrier separation by constructing a multivalent TiO2@Cu3(BTC)2 heterojunction photocatalyst toward enhanced photocatalytic hydrogen production

• A multi valence state TiO 2 @Cu 3 (BTC) 2 heterojunction photocatalyst was constructed. • The hydrogen production activity of TiO 2 @Cu 3 (BTC) 2 heterojunction photocatalyst has an enhancement of 72.2 times. • The enhanced activity was attributed to the formation of heterostructures and highly active Cu 2+ /Cu + mixed center. • Noble metal was not used in the photocatalytic hydrogen production process. • The photocatalyst exhibits self-repair capabilities without any treatment and maintains good stability for at least 200 days. Developing a low-cost, stable but efficient heterojunction photocatalyst is very crucial and challenging. A multivalent TiO 2 @Cu 3 (BTC) 2 heterojunction photocatalyst with active copper center has been prepared by a simple solvothermal method. In the photocatalytic process, photogenerated electrons produced by TiO 2 are transferred to the copper center in Cu 3 (BTC) 2 , partially reducing Cu 2+ and forming a highly active Cu 2+ /Cu + mixed center. This electron transfer path effectively increases the carrier density and prolongs the lifetime of the photogenerated charge. Under the optimal composite ratio, the hydrogen production activity of the TiO 2 @Cu 3 (BTC) 2 heterojunction photocatalyst was significantly enhanced, exceeding that of TiO 2 (8.39 μmol·g −1 ·h −1 ) by a factor of 72.2 times, and overcoming the barrier of no hydrogen production activity in pure Cu 3 (BTC) 2 . Additionally, the heterojunction photocatalyst demonstrated excellent chemical and photocatalytic stability over a period of at least 200 days. The enhanced photocatalytic activity is attributed to the improved visible light absorption efficiency, the effective heterojunction interfaces, particularly the highly active Cu 2+ /Cu + mixed center formed. Importantly, noble metal was not used in the photocatalytic hydrogen production process. Instead, Cu 2+ /Cu + were employed as active centers, making it possible to synthesize low-cost photocatalysts. This work provides conceptual guidance for the development of highly efficient multivalent TiO 2 -based heterojunction photocatalysts.