Metal-organic frameworks (MOF_s) are self-assembled molecular containers that can encapsulate and stabilize short-lived reaction intermediates. In this study, the Cu-benzene-1, 3, 5-tricarboxylate (BTC) MOF was incorporated in a ZnO/graphene oxide (GO) photocatalytic system by electrostatic interaction, and the obtained assembly showed improved hydrogen evolution activity. Electron spin resonance analysis was used to detect and monitor free radicals in the photocatalytic system, and demonstrated that Cu-BTC MOF could stabilize and extend the lifetime of free radicals, increasing the chance of H· radical recombination to form H₂. This work provides a new strategy for designing highly efficient photocatalysts.