Preparation Of Rigid Threedimensional Covalent Organic Frameworks Based On Carbazole And Spirofluorene For Separation And Catalytic Study

Covalent Organic Frameworks（COFs）as emerging porous crystalline polymer materials have attracted much attention recently.While numerous 2D COFs have been successfully synthesized,the exploration of 3D COFs is still in the early stages.Interestingly,3D COFs have a higher specific surface area,more stable structures with interspersion,and more diverse topological types.Notably,3D COFs are poorer to access than 2D COFs.This paper provides an overview of the research background on 3D COFs and presents a detailed account of the progress in their synthesis,properties,and applications.Building upon this foundation,a novel 3D COF with a four-fold interpenetration and dia topology is designed and synthesized.Subsequently,two new 3D COFs are obtained through reduction and carboxylation post-treatments of the designed COF.The structural properties and applications in gas adsorption and separation,catalytic chemical reactions,and photocatalysis are investigated.The specific research contents and conclusions are as follows:（1）An imine-linked 3D COF（SP-CA-COF-IM）is synthesized via Schiff base reaction.Subsequently,the imine bonds of SP-CA-COF-IM were reduced to amine bonds using a mild reducing agent Na BH（OAc）3to obtain the new 3D COF（SP-CA-COF-AM）.Fourier-transform infrared spectroscopy（FT-IR）and solid-state carbon spectroscopy confirm the successful synthesis of SP-CA-COF-AM,while powder X-ray diffraction（PXRD）and BET analysis demonstrate the preserved crystallinity and porosity of SP-CA-COF-AM.Importantly,the conversion of reversible imine bonds to secondary amine bonds enhances the structural stability of SP-CA-COF-AM.（2）Compared to SP-CA-COF-IM,the presence of secondary amine linkages significantly enhances the CO₂ adsorption capacity of SP-CA-COF-AM.Additionally,SP-CA-COF-AM exhibits catalytic properties resembling those of nanoenzymes.Its internally uniform pore structure enables selective catalysis of substrates with specific sizes in Knoevenagel condensation reactions,demonstrating excellent catalytic efficiency.Finally,utilizing the photoactivity of the carbazole functional group,CO₂ reduction to CO is catalyzed using SP-CA-COF-IM as a photocatalyst.Under sacrificial agent-free conditions,SP-CA-COF-IM achieves a CO production rate of 41.4μmol·g^-1·h^-1,positioning itself as a leading catalyst in terms of catalytic efficiency.（3）Modification of the 3D COF（SP-CA-COF-IM）is carried out through carboxylation,resulting in a new 3D COF（SP-CA-COF-COOH）.Characterization techniques such as infrared spectroscopy and solid-state carbon spectroscopy confirm the successful introduction of carboxylic acid functionality.Structural and property characterization of SP-CA-COF-COOH is conducted using powder X-ray diffraction,structure simulation,thermogravimetric analysis,BET surface area,and pore size analysis.The incorporation of carboxylic acid functional groups opens up additional applications for COFs and provides new avenues for their functionalization.