Construction Of Nickel-embedded Quinoline-bridged 2D-COFs And Study Of Their Enhanced Photocatalytic Ability Of Coupling Reactions

Organic conversion using semiconductor photocatalytic pathways provides a blueprint for green economic development.Compared with conventional non-homogeneous photocatalysts such as Ti O₂ and Cd S,covalent organic frameworks（COFs）have properties such as tunable structure,large specific surface area,high light absorption capacity,and long-range ordered structure.In particular,the long-range ordered structure provides a guarantee for the transport of photogenerated electrons,and the tunable structure provides guidance for the construction of active center systems,which make them promising for organic conversion applications.The most studied COFs are amine-substituted bonds,which are highly reversible and chemically unstable,and the polarization of amine-substituted bonds leads to weakenedπ-electron conjugation in the face,making it difficult to transport electrons during photocatalytic reactions.Therefore,it is a major challenge to construct highly stable and catalytically active COFs and to apply them in photocatalytic organic conversion.Based on this,the highly stable and catalytically active nonsubstituted quinoline-based 2D-COFs materials（NQ-COFs）containing active site exposure were innovatively prepared by a one-pot method in the presence of vinylidene carbonate using a metal rhodium-catalyzed C-H activation strategy in this paper,and the constructed Ni-NQ-COFs materials integrated photosensitizer and metal active center by embedding metallic nickel in the active site.The experimental results showed that NQ-COF_M3（bipyridine structure in monomer）and NQ-COF_G3（methoxy group in monomer）could be used for photocatalytic C-O/C-N and C-P cross-coupling reactions,respectively.The specific studies are as follows:（1）Non-substituted quinolinyl NQ-COF_M3 was synthesized by Schiff base reaction and prepared by a one-pot method using a metal rhodium-catalyzed[4+2]cyclization reaction,and the successful preparation of the material was subsequently confirmed by XRD,FTIR,HRTEM,SEM,and XPS characterization.The preparation of embedded Ni-COFs was achieved by directly introducing the metal Ni source,NQ-COF_M3 or COF_M3 into the photocatalytic C-O/C-N coupling reaction system,and Ni-NQ-COF_M3 has the dual effect of metal active center and photosensitizer.characterization experiments such as ICP-MS,XPS,FTIR,XRD confirmed the successful embedding of metal Ni into the active site.The photocatalytic C-O/C-N coupling reaction experiments confirmed the superior photocatalytic performance of NQ-COF_M3 compared with COF_M3,and the higher photoelectron migration efficiency and narrower optical band gap of NQ-COF_M3compared with COF_M3 were confirmed by DRS,Mott-Schottky curves,photocurrent and other photoelectric characterizations.The chemical stability test proved that NQ-COF_M3has higher crystallinity and stability compared to COF_M3.（2）The imine-based COF_G3,non-substituted quinoline-based NQ-COF_G3,was constructed using the same strategy described above.the successful preparation of COFs materials was confirmed using XRD,FTIR,SEM and other characterizations.The COFs materials were applied to the photocatalytic C-P cross-coupling reaction.The Ni-COFs containing embedded metal Ni were constructed by directly introducing the metal Ni source into the reaction system,and the successful embedding of the metal Ni into the active site was confirmed by FTIR,XRD,ICP-MS and other characterization experiments.The photocatalytic C-P coupling reaction experiments confirmed that（a）:NQ-COF_G3 has a superior photocatalytic performance compared to the pristine imine COF_G3.（b）:This N,O coordination of NQ-COF_G3 has a higher photocatalytic efficiency compared to NQ-COF_M3.The photoelectric characterization by DRS,Mott-Schottky curves,and photocurrent confirmed that NQ-COF_G3 has a narrower optical band gap and a wider visible light absorption range,resulting in a higher electron transfer efficiency.