Chain Regulation And Photocatalytic Performance Of Carbon Nitride-based Polymer

Graphite phase carbon nitride（g-C₃N₄）has important research value in environmental purification and solar energy conversion because of its high stability,non-toxic and suitable energy band structure.However,the highly symmetrical molecular structure of g-C₃N₄severely restricts electron delocalization,carrier migration,and exposure of active sites,resulting in low photocatalytic efficiency.The photocatalytic performance of g-C₃N₄can be improved by constructing heterojunctions and cocatalysts,but its essential defects cannot be changed.In view of the above shortcomings,this paper focuses on chain modification,breaks the symmetric structure of g-C₃N₄by simply constructing functional chain structure,and obtains carbon nitride photocatalytic materials with high activity.The structure-activity relationship between its structure,composition and activity was investigated by various characterization techniques.Specific innovative ideas are as follows:（1）A carbon nitride photocatalyst（COCN）modified with amphiphilic carbon and C-O-C chain was constructed by grafting polymerization of meleramine and formaldehyde.COCN-2 showed excellent sulfur oxidation and sulfone selectivity（about 100%）when it was used to oxidize thioether to produce sulfoxides.In addition,the material showed a good hydrogen production rate(34.9μmol h^-1)in the photocatalytic hydrogen production reaction,which was about 7 times that of the original g-C₃N₄.The structure-activity relationship study shows that amphiphilic carbon and C-O-C chain can not only act as the migration channel of photogenerated carriers,improve the migration rate of photogenerated carriers,but also regulate the adsorption performance on the catalyst surface and improve the photocatalytic activity.（2）g-C₃N₄-based polymer（PCON）with directed electron transfer channel was constructed by successfully embedding C-N and N-C-O chains into heptazine imide framework by copolymerization method.The embedding of the chain structure can not only directionally regulate the photogenerated carrier migration,but also optimize the adsorption and activation of N₂molecules,thereby improving the photocatalytic nitrogen fixation to ammonia efficiency(49.11μmol g^-1h^-1),which is about 11 times that of unmodified g-C₃N₄.