Study On Visible-Light Photocatalytic Degradation Of Endocrine Disruptors By Magnetic Nanomaterials

Due to the wide application of polycarbonate plastics and coating products,bisphenol A（BPA）has been widely used as an important organic chemical component.Current research shows that even though the content of BPA in the natural environment is low,its impact on human production and life should not be underestimated.In natural water bodies,BPA has a series of non-degradable characteristics such as low concentration,high stability,non-polymerization and hydrophobicity,so that it is difficult to effectively remove it via traditional wastewater treatment technologies.In recent years,photocatalytic technology has shown excellent performance in removing refractory micropollutants and therefore has received extensive attention.Titanium dioxide（TiO₂）has attracted much attention in the field of photocatalysis because of a series of photochemical advantages,such as stable chemical properties,low price,wide application range and strong stability.However,TiO₂has not been widely used because it cannot directly use visible light due to its wide band gap（3.0-3.2e V）.Carbon nitride（g-C₃N₄）has the advantage of relatively narrower band gap to partially absorb visible light.But the narrow visible absorption and fast electron-hole recombination still limits its practical application.This study is aiming to improving the photocatalytic activity and facilitating the postseparation process by constructing a novel nanocomposite with the current single photocatalyst TiO₂and g-C₃N₄.Using butyl titanate and melamine as precursors,ferroferric oxide（Fe₃O₄）as the magnetic medium,a novel magnetic visible-light nanocomposite photocatalyst TCNF_-5-500was prepared by a two-step method of hydrothermal calcination to explore the photodegradation of BPA.Different variables in the preparation process of TCNF_-5-500were studied systematically.The specific findings and conclusions are as follows:（1）The composite photocatalytic material TCNF_-5was prepared by a simple hydrothermal method.It was found via UV-vis spectroscopy that its light absorption boundary has been extended to about 500 nm,which is much higher than 385 nm of TiO₂and 460 nm of g-C₃N₄.With Fe₃O₄doping level of 5%,10%,15%and 20%in gradient,it is found that the magnetic properties（VSM）of the composites increase gradually as Fe₃O₄doping ratio increases,while the removal efficiency of BPA decreases gradually.Considering the balance between the removal efficiency of micropollutants and magnetism,the 5%Fe₃O₄doping concentration is chosen.（2）TCNF_-5-500composite photocatalyst was obtained by oxygen-free calcination of composite TCNF_-5at different temperatures.The morphology,microstructure,visible-light absorption,optoelectronic properties and thermal stability of TCNF_-5-500samples were systematically characterized by SEM,TEM,FT-IR,XRD,XPS,UV-Vis,TG and PL.The experimental results showed that in the presence of persulfate（PS）,when 2 mM PS and 50 mg TCNF_-5-500were added into 100 mL 10 mg/L BPA solution under 200 mW/cm²incident light intensity,the removal rate of BPA reached 100%within 20 min.The mechanism of micropollutant removal was further studied by free radical quenching experiment and electron paramagnetic resonance spectroscopy（EPR）.The results show that·SO₄^-,·OH,·O₂^-and h⁺can promote the removal of pollutants in this photocatlytic system.The BPA removal rate still reached more than 90%after five successive photodegradation and magnetic postseparation processes,which indicates that the TCNF_-5-500photocatalyst has value in practical application.（3）The efficient photodegradation of typical micropollutants,such as rhodamine B（Rh B）,paracetamol（AAP）,carbamazepine（CBZ）and phenol,by TCNF_-5-500shows that the prepared composite photocatalyst TCNF_-5-500has strong non-selective oxidation ability.Finally,the interfacial mechanism and BPA degradation path via the TCNF_-5-500/PS system were further analyzed and discussed,which provides a theoretical foundation for future practical applications.