Preparation Of Recoverable Type Ⅱ Heterojunction Fe₃O₄/ZnIn₂S₄ Photocatalyst And Its Degradation Pathway And Mechanism Of Gemifloxacin

Quinolone antibiotics are widely used in human medical,agricultural production,animal husbandry and aquaculture industries because of their excellent ability to inhibit microbial reproduction.However,the residual quinolone antibiotics in their production and use will enter natural water bodies through domestic and industrial wastewater,and accumulate and spread in the food chain,eventually posing a great threat to human health and ecological environment.Among the many methods to remove antibiotics from water,photocatalytic oxidation technology has a wide application prospect because of its environmental protection,green and high efficiency advantages.ZIS,as a ternary metal sulfide,exhibits excellent photocatalytic performance due to its large specific surface area,non-toxicity,adjustable bandgap,and excellent light absorption performance.However,a single photocatalyst has problems such as low separation efficiency of photo generated charge carriers and difficulty in recovery.However,photocatalysts suffer from problems such as low separation efficiency of photogenerated carriers and difficulties in recycling.To address these issues,this study aimed to construct a recoverable composite photocatalyst with ZnIn₂S₄（ZIS）as a substrate and Fe₃O₄ as a dopant.To investigate its photocatalytic degradation ability of quinolone antibiotics represented by Gemifioxacin（Gemifloxacin,GMF）.The main findings of this paper are as follows:（1）Fe₃O₄ semiconductor was successfully prepared by solvothermal method,and Fe₃O₄ was loaded onto the surface of ZIS by hydrothermal method,thus preparing Fe₃O₄/ZnIn₂S₄ composite material.Fe₃O₄/ZnIn₂S₄ was characterized by a series of means such as X-ray diffractometer and field emission scanning electron microscope.It was found that Fe₃O₄ was successfully introduced to the surface of ZIS nanospheres,which proved the successful preparation of Fe₃O₄/ZnIn₂S₄ heterostructure.The separation efficiency of Fe₃O₄/ZnIn₂S₄ photo generated carriers was significantly improved compared to Fe₃O₄ and ZIS,as confirmed by steady-state fluorescence spectroscopy,electrochemical impedance spectroscopy,and instantaneous photocurrent response intensity.Finally,the band structure of Fe₃O₄/ZnIn₂S₄ was analyzed using UV visible diffuse reflectance spectroscopy and Motschottky curve.Combined with the change of binding energy of each element in the X-ray energy spectrum,it is revealed that the electrons in the Fe₃O₄/ZnIn₂S₄ heterostructure are transferred from ZIS to Fe₃O₄,which proves that Fe₃O₄/ZnIn₂S₄ belongs to type II heterostructure.（2）GMF is selected as the representative of quinolones.Through the simulated sunlight experiment,it is found that GMF does not undergo photolysis.When the mass ratio of Fe₃O₄ to ZIS is 1:4,the preparation of Fe₃O₄/ZnIn₂S₄ heterojunction（M（0.04）ZIS）has the highest degradation efficiency of GMF.At 150 min,the degradation efficiency of GMF can reach 94.1%,and its degradation rate constant is 3.46 times and 47.13 times that of pure ZIS and Fe₃O₄.The effect of solution p H and humic acid（HA）on the degradation of GMF was investigated with M（0.04）ZIS heterojunction.The results showed that the photocatalytic degradation efficiency of GMF was the highest under neutral conditions（p H=6.67）,and the degradation efficiency of GMF decreased under acidic and alkaline conditions.The rate of decomposition decreases faster under strong alkaline conditions because the conditions of peracidity and alkalinity will affect the formation of·O₂^-.HA has a negative impact on the photocatalytic degradation of GMF by M（0.04）ZIS.HA and GMF compete in the adsorption sites and the active substances produced in the photocatalytic process.At the same time,due to the presence of HA,the light absorption efficiency of the photocatalyst decreases,resulting in a decline in the yield of active substances.Therefore,the higher the content of HA,the more obvious the inhibition effect on the photocatalytic degradation of GMF by M（0.04）ZIS.（3）The quenching experiments revealed that M（0.04）ZIS has its main role in the photocatalytic degradation of GMF by superoxide radicals（·O₂^-）and holes（h⁺）,with smaller hydroxyl radicals（·OH）.The sites that may be attacked during the degradation of GMF were predicted to be mainly concentrated in the quinolone ring part by the simplified reduced Fukui function（CFF）,and the GMF degradation products were analyzed by high performance liquid chromatography-ion trap-time of flight mass spectrometry to explore the pathways of GMF in photocatalytic degradation:defluorination,denitrogenation,hydroxyl substitution,and cleavage of pyrrole and pyridine rings.（4）The results of Three-Dimensional Excitation Emission matrix Fluorescence Spectrophotometer（3D-EEMs）showed that the intermediate products of GMF degradation were mainly humic acid-like organic compounds.Through the actual toxicity test of Escherichia coli,the toxicity of GMF degradation was reduced.Toxicity Estimation Software Tool software evaluates the toxicity of the degradation products of GMF,and its acute toxicity,developmental toxicity,teratogenicity and bioconcentration factors are significantly reduced,and the environmental risk is reduced.After five cycles,the photocatalytic efficiency decreased by 7.8%,the saturation magnetization of M（0.04）ZISdid not change significantly,and it still had good magnetic separation performance.