MOF-COF Composite Photocatalysts: Design, Synthesis, and Mechanism

Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) are widely used in photocatalysis for their high surface area, rich pore structures, and multiple active sites. Although photogenerated carriers generated by MOFs or COFs migrate through their respective active centers under visible light, the charge recombination exists in the MOFs or COFs. Therefore, researchers have constructed covalent bonds between MOFs and COFs as migration channels to effectively mitigate charge recombination. As is well-known, an MOF-COF as a signifcant semiconductor photocatalyst is a common choice for MOFs and COFs, but no systematic analysis of MOF-COF photocatalysts is known. On the basis of our group's research, this paper provides a detailed discussion of the design, synthesis, and mechanistic analysis of MOF-COF photocatalysts. First, we discuss MOF-COF heterojunction structures that can improve the photocatalytic properties of MOFs and COFs. Further, we cover the preparation of MOF-COF photocatalysts with core–shell and non-core–shell structures that are denoted MOF@COF and MOF/COF, respectively, according to different synthesis methods. Then we analyze the mechanisms of MOF-COF photocatalysts, involving photocatalytic hydrogen evolution (PHE) and photodegradation. Finally, we discuss the challenges and opportunities of MOF-COF photocatalysts. It is hoped that this review will facilitate the development and application of MOF-COF photocatalysts.