Performance And Mechanism Of Photocatalytic Degradation Of Fluvastatin By ZnIn₂S₄

In the past decade,Pharmaceuticals and personal care products?PPCPs?have become a new type of trace organic pollutants that have received extensive attention,and frequently detected in the aquatic environment.Occurrence of in aquatic environmental could have a great impact on the ecosystems.Fluvastatin is a synthetic statin drugs used to lower blood cholesterol levels and regulate blood lipids.Because of its pseudo persistence,bioaccumulation,strong biological activity and refractory characteristics,it has great risks to human health and environmental safety.Therefore,the degradation of fluvastatin through efficient,economical and environmentally friendly technologies has attracted enormous attention.Photocatalytic oxidation technology can completely mineralize organic pollutants into CO₂ and H₂O under mild conditions,which has broad application prospects in the field of wastewater treatment.ZnIn₂S₄ is a visible light photocatalyst,which could be preparated with mild reaction conditions.And it is stable and highly active.In this study,ZnIn₂S₄ was prepared by hydrothermal method and the physical and chemical properties of the catalyst was characterized by XRD,XPS,BET and UV-VIS.The performance of photocatalytic degradation of fluvastatin by ZnIn₂S₄ under 500 W Xe lamp irradiation was investigated.The effects of initial concentration of fluvastatin,ZnIn₂S₄ dosage,solution pH,light intensity,presence of anions and cations,and dissolved oxygen concentration on the photocatalytic degradation of fluvastatin by ZnIn₂S₄ were inveatigated,respectively.The free radicals generated during the photocatalytic degradation of fluvastatin by ZnIn₂S₄ were identified by situ capture experiments.The intermediate products produced during degradation were identified by liquid chromatography-ion trap-flight time mass spectrometer?LCMS-IT-TOF?.The possible degradation pathway and mechanism of fluvastatin degradation by ZnIn₂S₄were proposed.The degree of mineralization of fluvastatin and intermediates was determined by mineralization experiments.The main conclusions are as follows:?1?The ZnIn₂S₄ catalyst used in the experiment was prepared by low-temp template-free hydrothermal method.Its main constituent elements are Zn,In,S,which are in the valence states of Zn²⁺,In³⁺,and S^2-,respectively.And the crystal structure is hexagonal phase crystal.The BET surface area of the ZnIn₂S₄ sample is 81.744 m²/g,the pore size distribution is in the range of 2.2-169.7 nm,and the particles with a pore size of about 100 nm account for a larger proportion.The absorption threshold?g is608.9 nm.The bandgap of ZnIn₂S₄ is 2.036 eV,which could be excited by visible light.?2?After dark reaction for 40 min,the adsorption of fluvastatin by ZnIn₂S₄reached the adsorption equilibrium.When the initial concentration of fluvastatin was lower,the degradation rate was higher,and the degradation rate was the highest in the10 mg/L system.The degradation rate increases first and then decreases with the increase of the catalyst dosage.When the dosage of ZnIn₂S₄ is 0.2 g/L,the reaction rate of the photocatalytic degradation process of fluvastatin is obviously higher than the process reaction rate of other catalyst dosage.It is more favorable for the adsorption of fluvastatin on the surface of ZnIn₂S₄,the better the adsorption effect,the faster the degradation rate,and the higher the final degradation efficiency under the condition of pH=5.The concentration of ZnIn₂S₄ and fluvastatin was 0.2 g/L and 10 mg/L,respectively,and the optimal pH was close to 5.The degradation rate of fluvastatin reached 83.6%,and the mineralization rate reached 45.8%under optimal condition.?3?Aeration of oxygen gas increases the dissolved oxygen concentration in the system.O₂ adsorbed on the surface of the catalyst can be reduced as an electron acceptor.·O₂^-can directly oxidize fluvastatin to small-molecule organics.·O₂^-and H₂O The electrons further react to form H₂O₂,which is further decomposed into OH.H₂O₂and·OH can also oxidize fluvastatin to small molecular organics,which can promote the degradation of fluvastatin.The high-purity nitrogen will reduce the dissolved oxygen concentration in the system.As a result,the degradation rate of fluvastatin is also slowed down.?4?The main active free radicals in the reaction process were investigated by in-situ capture.·O₂^-was the main active free radical generated during the photocatalytic reaction,and the·OH and H₂O₂ played an auxiliary role.When the hole trapping agent is added,the binding of electrons and holes is inhibited,and more electrons migrate to the surface of the catalyst to react with oxygen to generate more·O₂^-,which increased the degradation rate of fluvastatin.?5?The intermediate products generated during the degradation process were identified by liquid chromatography-ion trap-time of flight mass spectrometry.It was suggested that the mechanism of degradation of fluvastatin is mainly superoxide radicals and hydroxyl radicals and hydrogen peroxide are used as secondary ligands to attack ring structures.Linear C-N bonds,C-C bonds,and C=C bonds in linear and cyclic structures form small molecule cyclic organics,linear organics,and hydroxylated derivatives,and the resulting intermediates are further oxidation and eventually decomposition into CO₂ and H₂O.Mineralization experiments showed that during the photocatalytic degradation of fluvastatin,part of fluvastatin was eventually oxidized to CO₂ and H₂O with a mineralization rate of 45.8%,and some intermediate products were not completely mineralized.?6?Results of intermediate toxicity evaluation showed that toxicity of intermediate product produced during the degradation process was lower than that of the bulk substance.The photocatalytic degradation of fluvastatin by ZnIn₂S₄ can effectively reduce the toxicity of fluvastatin.However,in the middle of the reaction,intermediate products with slightly higher risk were generated.Therefore,it is necessary to further study the degradation of intermediate products and to further explore the toxicology of intermediate products.