| In recent years,water pollution has become a key issue of concern.Water pollution not only hinders the development of social economy,but also poses a serious threat to the health of residents.Among many pollutants,antibiotic wastewater has become a kind of wastewater that is difficult to degrade due to its large amount of water,high concentration of organic pollutants,high toxicity and complex composition.Compared with other wastewater treatment methods,photocatalytic oxidation method has the advantages of stability,high efficiency and mild reaction conditions.In this study,molecularly imprinted Fe3O4/g-C3N4/TiO2 composites(MIP-Fe3O4/g-C3N4/TiO2)were prepared by hydrothermal method and molecular imprinting technique.Fe3O4 was introduced into g-C3N4 to give the material magnetic properties,which was convenient for subsequent recovery.The introduction of TiO2 to construct heterojunction can accelerate the separation of electron and hole pairs and effectively improve the degradation rate.The imprinted polymer was prepared,and the imprinted cavity was formed on the surface of the material,which could selectively adsorb and degrade the target pollutant,so as to prepare the MIP-Fe3O4/g-C3N4/TiO2 ternary composite material with excellent performance.MIP-Fe3O4/g-C3N4/TiO2 not only has good photocatalytic activity,excellent magnetic properties,but also has specificity,which can be used to degrade pollutants with high toxicity and low concentration in practical applications.The main content of this study is divided into the following four parts:Fe3O4/g-C3N4 materials were prepared by hydrothermal method using urea as precursor.The orthogonal test results showed that the photocatalytic effect was the best when the hydrothermal temperature was 200℃,the hydrothermal time was 14 h,the mass ratio of g-C3N4 to Fe(NO3)3·9H2O was 3:1,and the calcination time was 4 h.After continuous illumination for 120 min,81.23%of rhodamine B could be degraded.The results of photocatalytic activity test showed that the photocatalytic activity of Fe3O4/g-C3N4 was significantly enhanced compared with that of g-C3N4.This was because the introduction of Fe3O4 effectively inhibited the recombination of photogenerated electron-hole pairs and improved the photocatalytic reaction rate.Fe3O4/g-C3N4/TiO2 material was prepared by hydrothermal method using tetraisopropyl titanate as titanium source.The experimental results showed that when the addition amount of tetraisopropyl titanate was 20.0%,the photocatalytic activity was the highest.The degradation experiment of rhodamine B showed that the photodegradation efficiency of Fe3O4/g-C3N4/TiO2 material could reach 85.74%under visible light irradiation for 120 min,which was higher than that of g-C3N4 and Fe3O4/g-C3N4 materials.This is because the construction of heterojunction between TiO2 and g-C3N4 accelerates the formation of electron-hole pairs,resulting in significantly enhanced photocatalytic activity.MIP-Fe3O4/g-C3N4/TiO2 ternary photocatalytic material was prepared by molecular imprinting technique with chlortetracycline as template molecule and acrylic acid as functional monomer.The results showed that the photocatalytic effect was the best when the molar ratio of chlortetracycline to acrylic acid was 1:4.The reaction kinetics analysis showed that the k value of MIP-Fe3O4/g-C3N4/TiO2 was 0.0201,which was 4.57 times that of g-C3N4,indicating that the composite and imprinting had a significant effect on the improvement of the optical properties of g-C3N4.The MIP-Fe3O4/g-C3N4/TiO2 prepared under the optimal conditions was used to degrade the initial concentration of 20.0 mg/L chlortetracycline solution.The experimental results showed that the degradation rate of chlortetracycline by MIP-Fe3O4/g-C3N4/TiO2 reached 89.52%after 120 min of visible light irradiation.This is due to the presence of a large number of imprinted holes on the surface of MIP-Fe3O4/g-C3N4/TiO2,which can specifically adsorb and degrade chlortetracycline molecules.It can be seen from the selectivity experiment and stability experiment that MIP-Fe3O4/g-C3N4/TiO2 has specific recognition ability,and it still maintains high photocatalytic activity after 5 cycles.The results of free radical scavenging experiments showed that ·O2-and ·OH were the main active groups in the photocatalytic reaction process,and the possible degradation mechanism of MIP-Fe3O4/g-C3N4/TiO2 was deduced.The possible degradation pathway of CTC was speculated by LC-MS results:CTC molecules were decomposed by a series of oxidation,and finally CO2,H2O and other small molecules were formed.Finally,the degradation conditions of chlortetracycline were optimized.When the initial concentration of chlortetracycline solution was 10.0 mg/L,the initial pH value was 11,and the dosage of MIP-Fe3O4/g-C3N4/TiO2 was 1.25 g/L,the photodegradation efficiency was the highest,and the degradation rate of CTC could reach 95.87%after 120 min of illumination.In this study,the photocatalytic activity of g-C3N4 was improved by compounding,constructing heterojunction and introducing molecular imprinting technology,and the material was endowed with magnetism and specificity,which provided theoretical basis and new ideas for the research of g-C3N4 in the field of photocatalysis. |
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