Photocatalytic water splitting requires separation of the mixed H and O products and is often hampered by the sluggish O -producing half reaction. An approach is now reported to address these issues by coupling the H -producing half reaction with value-added benzylamine oxidation reaction using metal-organic framework (MOF) composites. Upon MOF photoexcitation, the electrons rapidly reduce the protons to generate H and the holes promote considerable benzylamine oxidation to N-benzylbenzaldimine with high selectivity. Further experimental characterizations and theoretical calculation reveal that the highly conjugated s-triazine strut in the MOF structure is crucial to the efficient charge separation and excellent photocatalytic activity.

The tailorable structure and electronic structure of metal−organic frameworks (MOFs) greatly facilitate their modulated light harvesting, redox power, and consequently photocatalysis. Herein, a representative MOF, UiO-66, was furnished by installing Fe 3+ onto the Zr-oxo clusters, to give Fe-UiO-66, which features extended visible light harvesting, based on metal-to-cluster charge transfer (MCCT). The Fe-UiO-66 with unique electronic structure and strong oxidizing power exhibits visible light-driven water oxidation, which is impossible for pristine UiO-66. More strikingly, under visible irradiation, the generated holes over Fe-UiO-66 are able to exclusively convert H 2 O to hydroxide radicals, initiating and driving the activation of stubborn C-H bond, such as toluene oxidation. The electrons reduce O 2 to O 2•radicals that further promote the oxidation reaction. The related catalytic mechanism and the structure−activity relationship have been investigated in detail. As far as we know, this is not only an unprecedented report on activating "inert" MOFs for photocatalytic C-H activation but also the first work on extended light harvesting and enhanced photocatalysis for MOFs by introducing an MCCT process.

For the first time, the photoexcited charge separation in a metal–organic framework has been evidenced with clear ESR signals, based on efficient and selective photocatalytic oxidative coupling of amines.