Design,Structure Regulation And Photocatalytic Performance Of Bismuth-based Perovskite Materials For Tetracycline Degradation

In recent years,the abuse of antibiotics has attracted much attention.Semiconductor photocatalysis technology has become an important method to control antibiotic pollution due to its advantages of driving by inexhaustible sunlight and mild reaction conditions.The Aurivillius(AL)bismuth base perovskite has a strong surface interface,an intrinsic dipole moment,and can generate an internal electric field,so it is beneficial to the separation of photogenic carriers.In addition,O 2p orbital and Bi 6s orbital hybridize to form a new energy level structure,which can reduce the band gap and extend the photoresponse range to the visible light area,which is a kind of photocatalyst with great potential.However,a single photocatalyst system has always faced difficult to balance the contradiction between narrow band gap and strong redox capacity,nor can it effectively inhibit carrier recombination.Therefore,reasonable design,modification and structure regulation of a single catalyst system have become the top priority for the development of photocatalytic technology.In this paper,two kinds of multilayer AL layered perovskites,SrBi4Ti4O15 and BisFeTi3O15,were prepared and designed.By constructing heterojunction means to improve the efficient of single catalyst system,and the synthesis of compounds had been used to characterize the crystal structure,physical and chemical properties,and studied the performance of composite photocatalytic degradation of tetracycline,explored the electronic transmission mode and the reaction mechanism,for the development of new photocatalyst and actual application provided a new train of thought.The main research contents are as follows:(1)SrBi4Ti4O15 layered perovskite materials were prepared by sol-gel method,molten salt method and hydrothermal method respectively.The as-prepared catalysts were evaluated by a series of physical and chemical properties characterization and catalytic performance experiments.The results showed that SrBi4Ti4O15 layered perovskite synthesized by hydrothermal method has the advantages of no impurities,uniform micro-morphology and superior photocatalytic performance(under 60 min visible light irradiation degraded 72.4%of tetracycline).According to the analysis of optical properties and band gap structure,SrBi4Ti4O15 has the ability to response visible light,and the positions of valence band and conduction band are calculated as 1.70 eV and-1.44 eV,respectively.In order to overcome the shortcomings of SrBi4Ti4O15 catalyst,which produces single free radical species in theoretically and has a wide band gap,g-C3N4 with strong visible light response and suitable valence band position was combined with SrBi4Ti4O15 by mechanical stirring method to form heterojunction catalyst.Optical property analysis shows that the band gap of g-C3N4 is 2.39 eV and the valence band potential is 1.81 eV.The photochemical experiments show that the separation ability of carrier generated by light excitation is improved.When the mass ratio of 5%g-C3N4 to 95%SrBi4Ti4O15,the composite sample showed the best photodegradation performance(80.94%)of tetracycline.The mechanism analysis showed that there are three kinds of reactive oxides spices produced in the reaction system--superoxide radical,hydrogen peroxide and hydroxyl radical.Finally,it was speculated reaction mechanism of TC photocatalytic degradation.(2)The heterojunction photocatalyst was formed by ZnFe2O4 in situ grown on two-dimensional Bi5FeTi3O15 nanosheets by hydrothermal method.The recombination improves the shortcoming of rapid recombination of electron-hole pairs on BisFeTi3O15,and at the same time balances the visible light responsiveness and redox ability.When the mass of Bi5FeTi3O15 is 35%,the composite sample shows the best degradation performance for tetracycline.According to the removal experiment of Chemical Oxygen Demand(COD)of real wastewater,the COD removal capacity of the sample meets the national discharge standard(GB18918-2002).In addition,due to the magnetic nature of ZnFe2O4,so the composite material is also magnetic and can be separated from the reaction system,which overcomes the shortcoming of photocatalyst can not be recycled by reaction system,meets the fundamental requirements of green chemistry,and provides a new idea for the practical application of wastewater treatment.The study of reaction mechanism showed that superoxide radical and hydroxyl radical gradually degraded tetracycline into small molecules and finally mineralized it.