Constructing Cu ion sites in MOF/COF heterostructure for noble-metal-free photoredox catalysis

Covalent organic frameworks (COFs) are an emerging type of visible-light-driven photocatalysts, yet the introduction of Pt cocatalyst is inevitable to achieve an efficient activity in most COF-based photocatalysts. Herein, we report a multifunctional MOF/COF heterostructured photocatalyst, Cu-NH2-MIL-125/TpPa-2-COF, with Cu ions immobilized by -NH2 groups of MOF, where the covalently connected heterojunction facilitates the separation of photogenerated charges and the monodispersed transient Cu2+/Cu+ centers serve as effective active sits. The resultant Cu-NH2-MIL-125/TpPa-2-COF (4:6) exhibits a visible-light-driven photocatalytic H2 evolution rate of 9.21 mmol·g-1·h-1, which is 7.3 and 17.7 times higher than that without Cu coordination and the pristine TpPa-2-COF, respectively, and superior to various reported COF and MOF-based photocatalysts without Pt. Moreover, the photocatalyst can efficiently oxidate amines to imines with high conversion rate (91.2 %) and selectivity (>99 %). The crucial role of Cu centers as active sites and its stability in long-term reaction was determined.