Structure Regulation Of Carbon-based Materials And Its Application In Photocatalysis

Polymeric carbon nitride（PCN）and its derivatives are considered to be an important class of carbon-based photocatalytic materials,which are widely used in the field of photocatalytic hydrogen production and photocatalytic degradation of pollutants.g-C₃N₄ is the most widely used PCN material,which has a high photo-generated electron hole pair（EHP）recombination rate and low photocatalytic performance.The photogenerated EHP recombination can be suppressed by the behavior of optimizing the structure of g-C₃N₄,which is an effective means to improve the performance of PCN catalysts.In this work,the g-C₃N₄ material was modified by metal ion doping and micro-morphology control,respectively.These works effectively improve the separation efficiency of photogenerated carriers and suppress the recombination of photogenerated EHP.Afterwards,CNx TiO₂homojunction-heterojunctions were constructed to improve the photocatalytic hydrogen production performance of the catalyst.The main resear ch contents and achievements of this dissertation are as follows:（1）Two different PCN materials were prepared by KOH hydrothermal etching method and molten salt method,named K-Poly（heptazineimide）（KCN）and Poly（triazineimide）/poly（heptazineimide）（MCN）,respectively.Afterwards,the effect of modification means on the coordination structure of atoms in the heterocycle of g-C₃N₄ molecule was investigated in this work.The PCN materials were characterized by steady-state fluorescence spectra and transient fluorescence spectra,and the results showed that the photogenerated EHP separation ability of KCN materials was improved by K element doping modification.Meanwhile,the carrier lifetime of the MCN material prepared by the molten salt method wa s found to be 4times longer than that of the g-C₃N₄ material.The PCN materials were tested for their photocatalytic performance.Compared with the original g-C₃N₄ material,the photocatalytic hydrogen production capacity of the two PCN materials was enha nced,and the enhanced photocatalytic degradation of methylene blue was exhibited by the MCN catalyst.（2）Homojunction-heterojunction poly（triazineimide）/poly（heptazineimide）/TiO₂（CNx TiO₂）materials were constructed to enhance the photocatalytic hydrogen production performance.The efficient photocatalytic degradation of methylene blue and the efficient photocatalytic hydrogen production are realized by CN x TiO₂catalyst,among which the hydrogen production rate of CN2TiO₂ catalyst can reach2594μmol·g^-1·h^-1,which is 5.5 times that of original g-C₃N₄ and 1.8 times that of original TiO₂.The structure of CN2TiO₂ was characterized.Compared with the catalyst components,the data showed that the absorption edge of the cataly st was red-shifted to 495 nm,and the forbidden band width was reduced to 2.66 e V,which effectively improved the light absorption performance of the catalyst.Meanwhile,the long carrier lifetime of MCN is inherited by CN2TiO₂ catalyst.The study of the atomic coordination structure of the catalyst shows that the MCN and TiO₂ in the homojunction-heterojunction catalyst are connected by triazine unit,which is the main site for the formation of the homojunction-heterojunction.More active sites for hydrogen production are induced by the construction of the heterojunction,the separation ability of EHP is further enhanced,the lifetime of the carriers between the energy bands is greatly increased,and the hydrogen production performance of the composite is significantly enhanced.