Synthesis And Photocatalytic Properties Of Covalent Organic Frameworks For CO₂ Photoreduction

Photocatalysis is an ideal green technology to solve the energy crisis and environmental pollution problem with broad application prospects.In recent years,metal organic frameworks（MOFs）have been reported as photocatalytic materials because of their highly ordered pore structure and ease of design,modification and modulation.Compared with MOFs,covalent organic frameworks（COFs）not only have similar advantages,but also are superior to MOFs in terms of thermal and aqueous stability even in acid and alkali environment.It means that this kind of material might have great potential in photocatalysis.While many research works have been done on the structure,photoelectric properties and catalytic activity of COFs,their photocatalytic properties have rarely been reported to date.In this thesis,we report on three kinds of COFs as promising photocatalytic materials with relatively high stability and enhanced photocatalytic activity,which is of great practical significance in expanding the application range of COFs and enriching the photocatalytic material system.First,we developed a novel solvothermal method to synthesize COF-1 and COF-5 without using the complex experimental procedures such as repeated freezing and thawing and vacuuming as reported in traditional method.The phase constitution,structure and morphology of the as-synthesized COFs were characterized.It is worthy to point out that the characterization of XRD and FT-IR shows that the synthesized COFs have good purity and crystallinity.By combining COF-5 with graphene to reduce the recombination of photo-generated electrons and holes,and photodepositing platinum nanoparticles as co-catalyst onto the active sites of the photocatalyst,the performance of photocatalytic reduction of carbon dioxide was 8 times higher than that of the COF-5 material particles.We also studied the synthesis and photocatalytic property of CTF.The experimental results showed that the stability of the material was extremely prominent,and the activity of photocatalytic reduction of carbon dioxide was higher than the activity of COF-5/graphene composites.In addition,CTF was synthesized by an ion-thermal method.The experimental results of photocatalytic CO₂ reduction showed that no decrease of activity was found after 50 hours of reaction,indicating the extreme stability of CTF upon reaction for photocatalytic CO₂ reduction.