Synthesis Of Heavy Atom-free Carbon Materials And Its Application For Photooxidation

Efficient selective photooxidation is a simple way to obtain complex organic oxidation products,which can effectively convert solar energy into chemical energy for storage,providing support for the sustainable use of energy.One of the keys to the efficient use of solar energy is to design and synthesize efficient photocatalysts in the field of photooxidation.Carbon quantum dots?CQDs?doped with metal atoms?including some heavy atoms?are prone to fluorescence quenching and deliquesced agglomeration,leading to difficult to store.In the first part of this paper,heavy atom-free CQDs prepared from Na₂[EDTA]and Na₂[PDTA]were used to investigate the effect of precursors with similar structure but different number of carbon atoms on the photooxidation based on the study of metal-doped CQDs before the research group.As a result,the P-350 prepared from Na₂[PDTA]with more carbon atoms has a higher degree of graphitization and a stronger electronic transmission capacity,its electron-accepting and-donating abilities were enhanced to 1.25and 1.28 times compared to E-350,respectively.Moreover,P-350 also showed high catalytic performance in the photooxidation of 1,4-dihydropyridine?1,4-DHP?,that the conversion of 1,4-DHP reached 98.02%during 90 min.However,compared to homogeneous catalysts?CQDs?,heterogeneous photocatalysts facilitate recycling,allowing products to be easily obtained.In recent years,singlet oxygen?¹O₂?sensitized by a triplet photosensitizer has been widely used in various photooxidation organic synthesis reactions.It was found that graphite phase carbonitride?g-C₃N₄?with conjugated structure has great potential in photooxidation as a heterogeneous catalyst,except that it has a poor ability to sensitize ¹O₂.In view of the insufficiency of the intersystem crossing?ISC?process in g-C₃N₄,the following two modification methods are proposed.One method is to introduce 3,3',4,4'-benzophenonetetracarboxylic dianhydride?BTDA?with high ISC efficiency as heavy atom-free spin converter to reduce the singlet-triplet energy gap(?E_ST)and hence generate ¹O₂ effectively.In addition,DFT calculations and experimental verification also confirmed that matching the energy level of the ligand?melem?with the spin converter is also beneficial for promoting the ISC process.In the photooxidation of 1,5-dihydroxy-naphthalene?1,5-DHN?,CN-T shows excellent photocatalytic selectivity,and the highest yield of Juglone can reach 71.8%after irradiation for 60 min,which was increased 1.34 times compared with cyclometalated Pt^II complexes?53.6%?in homogeneous photooxidation.Another method is to use a triplet inducer——1-pyrenecarboxylic acid?PCA?as heavy atom-free triplet acceptor molecule to achieve continuous transfer of triplet excitons within the g-C₃N₄ to the catalytic system.Time-resolved fluorescence spectroscopy demonstrated that the combined PCA acts as a transfer medium for triplet excitons,resulting in the promotion of ISC process,thereby generating ¹O₂ effectively.In the photooxidation of uric acid?UA?,pg-C₃N₄/PCA shows excellent photocatalytic selectivity,and the conversion of UA can reach 91.32%after irradiation for 60 min.