Preparation Of Fe₃O₄@SiO₂@TiO₂ And The Photocatclytic Degradation And Mechanism Of Sulfonamides In Aqueous Solutions

Though sulfa drugs have made a great contribution to stock breeding and disease treatment, its extensive use and even abuse has also brought many environmental problems. Thus, these emerging contaminants increasingly occurred in wastewater and aquatic environments. However, antibiotic drugs’ removal is difficult and generally inefficient in traditional wastewater treatment plant; hence, sulfa antibiotics residue has caused a potential threat to aquatic organisms and human health. The advanced oxidation methods such as photocatalysis TiO2 is an important method of removal of organic pollutants in water. In this work, in order to develop a new kind catalyst with high photo-activity and convenient recyclability, by using the ultrasonic-assisted modified Stober method and sol-gel approach, the magneticγ-Fe2O3@SiO2@TiO2 (FST) microspheres of core-shell structure were prepared at the low-temperature synthesis condition. Besides, the photo-activity ofγ-Fe2O3@SiO2@TiO2 was evaluated by through the photo-degradation of sulfamethazine (SMZ) in water. And its structures have been characterized by XRD,SEM, Fourier transform infrared spectroscopy, UV - vis, and VSM. In combination with HPLC/ESI-MS analysis and density functional theory, degradation pathway of sulfamethazine had been speculated.Results suggested that the SiO2 interlining could directly block the contact of electron injection from TiO2 to γ-Fe2O3 which could be verified by the Fourier transform infrared spectroscopy analysis. And the good superparamagnetic properties of γ-Fe2O3@SiO2@TiO2 could be reserved by the formation of γ-Fe2O3,which might greatly guarantee the magnetic separation effect of theγ-Fe2O3@SiO2@TiO2 catalytic. Also, the photo-degradation of sulfamethazine demonstrated that the prepared γ-Fe2O3@SiO2@TiO2 could provide the same high photo-activity as that of P25 TiO2 because of their similar constitutes of anatase and rutile types, and the degradation rate of sulfamethazine reached to 95% (UV irradiated for 1hr and/or solar radiation for 2 hr) by using the both photo catalysts.Moreover, this easily magnetic-recoverable γ-Fe2O3@SiO2@TiO2 NPs could be reused at least five times without any appreciable reduction of photo-catalytic efficiency. All these demonstrated the successful and hopeful prospect of this prepared γ-Fe2O3@SiO2@TiO2 at lower-temperature comparing with the traditional heat synthesis approach. For another, degradation mechanism of sulfamethazine were studied in detail. And some key reaction processes as the hydroxyl oxide, ammonia oxidation, splitting decomposition and open loop reactions might have occurred during the photo-degradation of sulfamethazine.Therse sulfa drugs have a similar conclusion, thus a comparative analysis of the degradation regularity of sulfonamides were carried out.The research provides the theoretical basis of degradation for sulfa drugs which is difficult to biochemical treatment, and further provides scientific basis of photodegradation and conversion process in the aquatic environment.