Integrating hollow spherical covalent organic frameworks on NH2–MIL-101(Fe) as high performance heterogeneous photocatalysts

Abstract

A novel metal–organic framework@covalent organic framework (MOF@COF) heterojunction was synthesized based on post-synthetic covalent modification. In the present work, aldehyde-modified MOFs (NH₂–MIL-101(Fe)) were covalently bonded with covalent organic frameworks (Schiff base network-1, SNW-1) forming the NH₂–MIL-101(Fe)@SNW-1 (MS-x) heterojunction by using this strategy. The MS-x heterojunction showed excellent photodegradation ability for pollutants and photocatalytic hydrogen production under simulated sunlight. The superior photocatalytic performance of the MS-x heterojunction can be attributed to the formation of –CN– bonds between NH₂–MIL-101(Fe) and SNW-1, which enhances the charge separation efficiency and improves the stability of the photocatalyst. It is worth mentioning that SNW-1 on the surface of the catalyst had a hollow structure which can promote the photoelectric charge migration. Furthermore, the results verified that the matched band structure of NH₂–MIL-101(Fe) and SNW-1 could induce a type II heterojunction, which could well explain the improved photocatalytic performance of the photocatalytic system. This work not only provides a new idea to construct highly efficient and stable MOF@COF heterojunctions but also broadens the applications of COF-based materials.