Preparation And Photocatalytic Properties Of Metalloporphyrin Covalently Linked G-C₃N₄

Graphitic carbon nitride（g-C₃N₄）has attracted much attention as a heterogeneous photocatalyst due to its high thermal and chemical stability,tunable band gap,suitable valence band position,customizable texture and low cost.However,g-C₃N₄ suffers from low photocatalytic efficiency on account of the high recombination rate of photogenerated carriers.Numberous studies have shown that metalloporphyrins as photosensitizers exhibit good visible light absorption,and absorb light in the range of 400-700 nm.In adition,the presence of metal active sites can effectively transfer and capture electrons.By covalently immobilizing metalloporphyrins on g-C₃N₄,the band structure and charge carrier separation can be greatly improved.Therefore,a strong chemical bond is used to couple the metal complex with g-C₃N₄ in this thesis.By adjusting the doping ratio of the precursor and the polymerization temperature,a series of novel covalently linked g-C₃N₄by cobalt porphyrin/iron porphyrin photocatalysts were designed.The covalent bands present in these photocatalysts can act as electron transfer channels between porphyrins and photocatalysts,further promoting the delocalization of porphyrinπ*orbitals,which not only enables successful tuning of the band structure and charge carriers of g-C₃N₄,but also expands the light absorption range of photocatalysts.Furthermore,the best properties of homogeneous and heterogeneous catalysts are combined to improve their activity towards chemical reaction processes and enhance the recyclability of the catalysts.The results show that the metalloporphyrin can be successfully anchored in the framework of g-C₃N₄,realizing the optimization of the electronic and energy state structure.Meanwhile,the metalloporphyrin basic unit can be maintained in the composite structure,providing a highly active reaction center for the catalyst.For the covalently linked g-C₃N₄ material（Co PP-CN）with cobalt porphyrin,Co PP-CN exhibits good catalytic performance for olefin epoxidation.For iron porphyrin covalently linked g-C₃N₄（Fe PP-CN）,Fe PP-CN-2 shows extraordinary high activity and selectivity over the semi-dehydrogenation reaction from 1,2,3,4-tetrahydroisoquinoline（THIQ）to 3,4-dihydroisoquinoline（3,4-DHIQ）.Both materials show high catalytic activity,excellent selectivity,general applicability to extended substrates,and good recyclability,with potential for practical use.