Effect Of Aggregate Structure Of Polyimine On Its Photocatalytic Disinfection Performance

The photocatalytic disinfection technology of semiconductors has attracted great research interest due to its cost-effectiveness,in situ generation of active oxide species and environmental friendliness.Among them,polymer semiconductor photocatalysts have become a hot research topic in recent years because of a series of advantages such as no secondary pollution,visible light absorption ability and energy band structure and a large number of modifiable active sites.However,most of the polymer semiconductor photocatalysts suffer from serious photogenerated carrier complexation problems,which affect their bactericidal activity.Therefore,providing a driving force for photogenerated carrier separation to improve photocatalytic activity has become the key to this research area.The built-in electric field can be used as a driving force for semiconductor photocatalysts at the material level,however,there is still a gap in the study of polymer semiconductor aggregate state structure and built-in electric field,photocatalytic activity.In this paper,we systematically explored the effects of polymer semiconductor crystalline state,crystal symmetry on the built-in electric field,photogenerated carrier separation and transport,and visible light-driven sterilization ability using linear polyimide as the research object,and obtained the following results.1.In order to investigate the effect of crystallinity of conjugated polymers on their built-in electric field construction and photogenerated carrier separation and transport ability,linear polyimide ODA-BPAH was synthesized by Schiff base reaction using 4,4’-diaminodiphenyl ether(ODA)and 4,4’-biphenyl dicarboxaldehyde(BPAH),and ODA-BPAH with different crystallinity was obtained by adjusting the reaction solvent The ultrathin nanosheet morphology exhibited by the high crystallinity ODA-BPAH provides a shorter transport distance for photogenerated carriers,thus reducing the probability of their complexation.The highly ordered arrangement of dipoles due to high crystallinity makes high crystallinity ODA-BPAH possess a strong built-in electric field,which can be used as a driving force for the separation and transport of photogenerated carriers at the material level.Transient and steady-state fluorescence spectroscopy and electrochemical tests demonstrate that the photogenerated carrier separation and transport efficiency of high-crystallinity ODA-BPAH far exceeds that of low-crystallinity ODA-BPAH.2.In order to provide material-level photogenerated carrier separation driving force for polymer semiconductors,a strategy to modulate the crystal symmetry of highly crystalline polyphenyleneimine for enhancing the built-in electric field is proposed,and the feasibility of this strategy is verified by selecting linear polyphenyleneimine as a model polymer.Two highly crystalline linear polyphenyleneimines,PDA-PAH and PDA-MAH,were obtained by the condensation of p-phenylenediamine(PDA)as the diamine monomer and p-phenylene terephthalaldehyde(PAH)and m-phenylene dialdehyde(MAH)as the dialdehyde monomer through the Schiff base reaction.The two highly crystalline polyphenyleneimines are ultrathin nanosheet materials with similar thicknesses and share similar light absorption and energy band structures.When the molecular symmetry of the benzaldehyde monomer is reduced from D2h of PAH to the C2v point group of MAH,the corresponding crystalline symmetry of the polyphenyleneimine also appears to be reduced accordingly.pDA-PAH is an orthorhombic crystal system with a space group of Pmcm and a crystal center of symmetry.The non-centrosymmetric crystal structure of PDA-MAH generates a dipole moment in the lattice and builds a strong internal electric field at the material level.This built-in electric field drives the photogenerated carrier separation and transport process of PDA-MAH,which gives it better photogenerated carrier separation ability compared to PDA-PAH.3.In order to explore the application prospects of polyimine-based conjugated polymers in photocatalysis,we tested the visible light-catalyzed bactericidal ability of the obtained ODA-BPAH and polyphenyleneimine with different crystallinity using E.coli as a model bacterium,and found that the high crystallinity ODA-BPAH and PDAMAH with the best photogenerated carrier separation and transport performance exhibited the best visible light-driven bactericidal Both could inactivate>99.9999%of E.coli in 45 min under visible light irradiation,which exceeded all non-precious metal photocatalysts reported so far.We then selected Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus,resistant to S.aureus to further validate the fast and broad-spectrum bactericidal performance of high crystallinity ODA-BPAH and PDA-MAH.We demonstrated the mechanism of photocatalytic bactericidal activity of high crystallinity ODA-BPAH and PDA-MAH by quencher,SEM,HIM,and fluorescence staining experiments,which is the destruction of bacterial cell wall by H2O2,a reactive oxygen species,leading to cytoplasmic efflux and bacterial death.