Research Of Photocatalytic Degradation Of Tetracycline Based On The Immobilized ZnIn₂S₄ System

During the rapid development of photocatalytic technology,many researches including the photocatalytic modification,photocatalytic degradation mechanism,new photocatalytic materials have been investigated,which provide ample experimental support and strong theoretical basis for the application of photocatalytic technology in environmental field.However,there are a series of problems in practical application of photocatalytic technology,such as the higher recombination rate of electron-hole pairs,lower photocatalytic activity,separation and recycling of powder photocatalysts from the reaction system.At present,the combination of photocatalytic technology with other technology has a broad application prospect owing to its synergistic effect,which includes the coupling of photocatalytic technology with membrane treatment and photoelectrocatalytic technology.In order to overcome the disadvantages of powder photocatalyst,the immobilization of ZnIn₂S₄ on PVDF membrane and flexible PAN-graphite felt by different synthetic method was conducted for this study.The samples were characterized by means of SEM,EDS,XRD and AFM,Zeta potential.The removal mineralisation rates were used to evaluate the degradation effect of tetracycline.Results were as follows:Photocatalytic functional layer was formed through the filtration of ZnIn₂S₄suspension synthetized by hydrothermal method on PVDF membrane,which constituted the dynamic photocatalytic membrane reactor?DPMR?.Operating with effluent circulating to the photocatalytic membrane reactor,the highest TOC removal efficiency of 57%was obtained after 3 h reaction with 1.88 mg/cm² photocatalyst under the flux of84.06 L/m²/h and light intensity of 50 mW/cm².Operating with continuous influent and effluent mode under the flux of 26.09 L/m²/h,hydraulic retention time?HRT?of 7.4 h and light intensity of 50 mW/cm²,an average of 50%removal efficiency can be maintained during the 24 h photocatalytic reaction with photocatalyst loading of 1.88 mg/cm² and initial tetracycline concentration of 10 mg/L.Under the same operating conditions,more than 92%removal efficiency can be maintained during 36 h photocatalytic reaction when lower initial concentration of 100?g/L was applied.After this reaction,the characterizations of SEM,Zeta potential,Contact angle and AFM showed that the surface and structure of PVDF basement membrane were not affected.By the one-step hydrothermal method,the ternary ZnIn₂S₄ with the morphology of microspheres were fabricated on flexible PAN-graphite felt?PAN-GF?,which construct-ed trielectrode photoelectrocatalytic degradation system.The photoelectronchemical performances were evaluated by transient photocurrent response?I-T curve?,cyclic voltammetry?CV?,linear sweep voltammetry?LSV?and electrochemical impedance spectroscopy?EIS?.The sample with the thickness of 5 mm,normal percursor solution and 1 ZnIn₂S₄ coating layer showed the best photoelectronchemical property.The scanning electron microscopy?SEM?of 5 mm GF-ZIS?1?-1 showed that the fabrication of ZnIn₂S₄ started from the formation of net-like nanosheet film on GF substrate and then followed with the growth of microspheres on the nanosheet layer.More ZnIn₂S₄ layers in turn led to a compact blocked structure and further deteriorated the photoelectrochemical properties.The best 64%photoelectrocatalytic mineralisation of tetracycline was achieved by the direct?DC?current mode at anodic bias of 0.9 V after 3 h photoelectrocatalytic process,and at the same time,the removal of TC was 94%based on 357 nm,while it was 79%when based on 275 nm.Photogenerated holes played the dominant role in the anode PEC process and oxidation assisted by electrode improved its degradation efficiency.