Construction of core–shell MOF@COF hybrids with a Z-scheme heterojunction for efficient visible light photocatalysis

Abstract

Metal–organic frameworks (MOFs) have emerged as promising photocatalysts due to their tunable architectures and semiconductor-like behavior. However, their photocatalytic efficiency is often hampered by suboptimal light utilization and fast charge carrier recombination. To address these challenges, we developed core–shell MOF@COF Z-scheme hybrids, where a covalent organic framework (COF, TpBD-COF) was coated on the NH₂–UiO-66 surface via imine bond interconnection. Characterization and DFT calculation results suggested the formation of a well-contacted interface, as well as a Z-scheme heterojunction between the NH₂–UiO-66 core and TpBD-COF shell. The TpBD-COF shell with an inherently narrow energy band contributed to the visible light absorption, while the fabricated Z-scheme heterojunction resulted in the spatial electron–hole (e⁻–h⁺) separation and high redox ability. By rationally controlling the ratio of NH₂–UiO-66 and TpBD-COF precursors, the tailored thickness of the TpBD-COF shell was achieved, which could modulate the Z-scheme heterojunction interface, and thus optimized the photocatalytic performance. The core–shell MOF@COF hybrids were highly efficient in visible light-driven oxidative coupling of amines to imines in air without the need for any sacrificial agents. Almost quantitative conversion (94%) of benzylamine to N-benzylidenebenzylamine was achieved over optimal NH₂–UiO-66@TpBD-COF(21.9), which is approximately 4.0 and 1.5 times that of pristine NH₂–UiO-66 and TpBD-COF, respectively. The superior catalytic performance, coupled with benign reaction conditions (visible light, room temperature, ambient air), makes NH₂–UiO-66@TpBD-COF(x) highly promising for solar utilization in green synthesis.