Performance And Mechanism Of Ketone Group Tuning Covalent Organic Framework Materials For Catalytic Oxidation Of Tetracycline In Water

In the past few decades,with the rapid development of agriculture and medical health,the concentration of antibiotics in surface water,wastewater and drinking water has far exceeded the standard.As a well-known broad-spectrum antibacterial agent,tetracycline（TC）is widely used to treat and prevent human and livestock diseases.Unfortunately,due to poor biological absorption and metabolism,TC accumulates in a large amount in the aquatic environment,which poses a serious threat to the ecosystem and public health.Therefore,there is an urgent need to find an efficient and economical treatment technology to remove TC in wastewater.Compared with traditional wastewater treatment methods（such as adsorption,biological processes,membrane filtration,etc.）,photocatalytic oxidation technology is considered an efficient,low-cost and environmentally friendly technology for the TC treatment in water.However,in actual operation,the low utilization rate of visible light and the insufficient catalytic degradation of pollutants seriously affect its practical application.Therefore,this paper uses the enol-ketone isomerization reaction to design（X%[C=O]-COFs）COFs catalysts with different amounts of ketone groups,based on ketone-based COFs construct different visible light catalytic systems,investigate the performance of visible light catalytic removal of TC in water,clarify the structure-performance relations between its ketone structure and visible light catalytic performance.The concurrent photocatalysis-persulfate activation（CPPA）system with ketone-based COF as a catalyst was further constructed to improve the TC degradation effect.The effectiveness of ketone-based COF as a visible light catalyst for TC degradation in the CPPA system was clarified,and the influence of different environmental factors on the removal of TC in the CPPA system was analyzed.Reveals the visible light catalysis mechanism of the ketone group tuning COFs and the catalysis mechanism of ketone-based COF in CPPA system are revealed.The synergistic mechanism of visible light catalysis and persulfate catalysis in CPPA system are investigated,and the stability and recyclability of ketone-based COF is evaluated.The main results were shown as follows:（1）.This paper uses the enol-ketone isomerization reaction to design and synthesize different forms of ketone group tuning COFs catalysts.With the increase of the relative content of ketone groups,the corresponding COFs catalysts exhibit excellent performance,such as high electron-hole separation rate and high electron transfer rate.（2）.The 100%[C=O]-COF with the highest relative ketone content shows the best catalytic performance in the visible light catalytic system and the CPPA system.Under visible light,the degradation rate constant of TC（20 mg/L）in the 100%[C=O]-COF visible light catalytic system is 1.46,2.04,2.49 and 3.69 times that in the 75%[C=O]-COF,50%[C=O]-COF,25%[C=O]-COF and 0%[C=O]-COF visible light catalytic system,respectively.In the CPPA system,the degradation rate constant（50 mg/L）of TC is 1.73 times that of the 100%[C=O]-COF/PMS system and 3.32 times that of the 100%[C=O]-COF visible light catalyst system.（3）.The ketone group linearly changes the conduction band/valence band position,surface Zeta potential and other properties of the COFs catalyst to inmenifest the different visible light catalytic performance.With the increase of the relative content of ketone groups in the COFs catalyst,the conduction band position of the COFs catalyst gradually decreases and the valence band position gradually increases,and the corresponding active species that dominate the degradation of TC in the corresponding visible light catalytic system change accordingly.With the increase of the relative content of ketone groups,the main active substance in the corresponding visible light catalytic system changes from the combined effect of O₂·^–and h⁺to the direct oxidation of h⁺.（4）.The C=O structure and N-containing functional groups in 100%[C=O]-COF as active sites in the CPPA system participate in the synergistic effect of visible light catalysis and persulfate catalysis.The addition of PMS promoted the separation and transportation of the photogenerated carrier in the COFs catalyst,and promoted the activation and decomposition of PMS.In the CPPA system,a large amount of reactive species(·OH,SO₄^·–,O₂·^–,h⁺and ¹O₂)are produced to attack TC,thereby enhancing the TC degradation.Among them,h⁺and ¹O₂ are the dominent reactive species,which can achieve high-efficiency degradation of TC and removal of TOC in the system.Based on the above results,this study provides a reference for the application of COFs catalysts in the removal of environmental organic pollutants,provides a theoretical basis for elucidating the structure-performance relations between catalyst molecular structure and catalytic activity,provides technical support for the construction of concurrent photocatalysis-persulfate activation system,provides new insights and scientific theoretical methods for removing tetracycline antibiotics in the environment.