Construction Of Novel Covalent Organic Frameworks And Application In Photocatalytic Degradation Of Tetracycline

Tetracycline is a class of antibiotics with broad-spectrum antibacterial activity,but its abuse in aquaculture and poultry raising has caused serious harm to ecological environment and human health,and has become a public environmental problem that needs to be solved urgently,therefore,remediation of polluted soil and water bodies through degradation of tetracycline has always been an important topic at present.In which,photocatalytic degradation has become an important method for degradation of tetracycline by virtue of environmental friendliness and high degradation efficiency.Covalent organic framework materials are a class of crystalline porous materials interconnected by strong covalent bonds,exhibit a suitable energy band structure and good light absorption performance due to their unique structure and characteristics,and expected to be ideal photocatalytic materials.Therefore,in this thesis,simple construction methods of covalent organic framework materials were established firstly,and then three covalent organic framework materials were successfully synthesized by them,their structure,morphology and characteristics were systematically characterized;and their catalytic performances in the photodegradation of tetracycline were examined,the research achivements are as follows:（1）Based on the unique spectral response and electron transport properties of the azobenzene structural unit,a covalent organic framework material Tp-Azo containing azo units was obtained from 2,4,6-triformylphloroglucinol（Tp）and4,4’-diaminoazobenzene（Azo）monomers;the characterization results indicated the good crystallinity of Tp-Azo.In the experiment of photocatalytic degradation of tetracycline,Tp-Azo showed excellent degradation efficiency（66.6%）.（2）The modified covalent organic framework Cu-Tp-Azo was obtained by immobilizing copper ions on Tp-Azo by impregnation method,the characterization results indicated that the introduction of copper ions in Cu-Tp-Azo did not destroy the crystal structure of Tp-Azo,and XPS analysis showed the existence of copper element in the form of Cu²⁺.In the experiment of photocatalytic degradation of tetracycline,compared with Tp-Azo,Cu-Tp-Azo displayed higher degradation efficiency（83.6%）,indicating that the modification of copper further improved the photocatalytic activity of Tp-Azo,which is consistent with the evaluated results of photoelectric performance.The above results show that the doping of transition metal copper into the covalent organic frameworks can increase the adsorption sites of tetracycline on the one hand,and on the other hand it can effectively regulate and optimize the electronic structure of Tp-Azo,effectively inhibit the recombination of photo-generated electron-hole pairs,and improve the separation efficiency of photo-generated carriers,which may be beneficial to improve its photocatalytic activity.（3）Based on the unique nitrogen-rich structure and the suitable band gap for photocatalysis of triazine covalent organic framework materials,a covalent organic framework TT-COF with triazine ring was successfully synthesized from2,4,6-triformylphloroglucinol（Tp）and 2,4,6-Tris（4-aminophenyl）-1,3,5-triazine（TAPT）monomers by monomer exchanging strategy.First,imine small molecules are formed through rapid and irreversible monomer condensation reaction,then triazine covalent organic framework materials were synthesized by reversible aldehyde monomer exchange.Compared with the traditional solvothermal method,this method is more simple and efficient.The XRD results showed that the crystallinity of TT-COF was similar to that of COF prepared by solvothermal method.It was found that TT-COF showed better performance in photocatalytic degradation of tetracycline（86.8%）.Their optical performances show that TT-COF has relatively narrow optical band gap and wide light absorption range,which is conducive to the separation of internal photogenerated carriers,and further improve its photocatalytic activity.