Covalently integrated core-shell MOF@COF hybrids as efficient visible-light-driven photocatalysts for selective oxidation of alcohols

Building a covalently connected structure with accelerated photo-induced electrons and charge-carrier separation between semiconductors could enhance the photocatalytic performance. In this work, we report a facile and novel seed growth method to coat NH2-MIL-125 MOFs with crystalline and porous covalent organic frameworks (COFs) materials and form a range of NH2-MIL-125@TAPB-PDA nanocomposites with different thicknesses of COF shell. The introduction of appropriate content of COF could not only modify the intrinsic electronic and optical properties, but also enhance the photocatalytic activity distinctly. Especially, NH2-MIL-125@TAPB-PDA-3 with COF shell thickness of around 20 nm exhibited the highest yield (94.7%) of benzaldehyde which is approximately 2.5 and 15.5 times as that of parental NH2-MIL-125 and COF, respectively. The promoted photocatalytic performance of hybrid materials was mainly owing to the enhanced photo-induced charge carriers transfer between the MOF and COF through the covalent bond. In addition, a possible mechanism to elucidate the process of photocatalysis was explored. Therefore, this kind of MOF-based photocatalysts possesses great potentials in future green organic synthesis.