Study On The Regulation Of Photoinduced Charge Behavior And Performance Of Polymer Photocatalysts

Polymeric photocatalysts have been rapidly developed in the scenario of photocatalysis,especially in photocatalytic water splitting and CO₂ reduction,owing to their merits of multiple compositions and easily tailored band structures.However,the photocatalytic efficiency is restricted by their relatively high exciton binding energy（E_b）and severe charge recombination process.Therefore,it is the key to effectively regulating the charge separation,migration and transfer process of the polymers to achieve a high-efficiency photocatalytic reaction system,which remains a critical scientific issue.In this context,many strategies are proposed to optimize the process of photogenerated charge separation and migration as well as transfer in polymers,such as morphology control and the construction of heterostructures,which results in a high-efficiency photocatalytic reaction system.The main research contents and results are as follows:（1）two-dimensional porous carbon nitride nanosheets（CNS）are successfully prepared by adding industrial catalysts during polymerization,in which the ammonia releasing kinetics are accelerated.Such a porous nanosheets structure can promote the bulk and interface charge transfer,leading to an enhanced photocatalytic hydrogen evolution activity;（2）Van der Waals heterojunction between covalent organic framework（COF）and carbon nitride is formed via intermolecular?-?interaction,which can improve the spatial isolation of the charges between two semiconductors,and thus highly enhanced the photocatalytic performance of hydrogen evolution;（3）two novel thiophene-based conjugated polymers with one-dimensional（1D）and three-dimensional（3D）molecular structures are designed and prepared.The results show that the E_b of 3D polymer is lower than that of 1D polymer,which implies that the excitons are easier to dissociate into free charge,resulting in higher photocatalytic water splitting performance in 3D configuration;（4）a ternary acceptor-donor-acceptor（A₁-D-A₂）molecular junction is established via gradient nitrogen substituting into the polymer skeleton,which can optimize the intermolecular charge transfer process.An apparent quantum yield of 26.6%at 405nm is achieved on the best photocatalyst,exceeding most polymer photocatalysts.The innovative aspects of the thesis include:（1）a novel industrial catalyst-assisted synthetic method is proposed to carbon nitride nanosheets,which provides a new way to prepare CNS on a large scale;（2）all organic polymer heterojunction is established between a hydrazone-linked COF and carbon nitride,and guides a new direction for the construction of all organic photocatalysts with polymer heterojunctions;（3）the E_b is reduced by adjusting the dimensionality of the polymers,thus improves the efficiency of exciton splitting;（4）asymmetric A₁-D-A₂polymers are constructed,and high photocatalytic hydrogen production efficiency is realized due to the fast intermolecular charge carrier transfer.