Photocatalytic Degradation Of Pharmaceuticals And Inactivation Of Ubiquitous Pathogens In Water As Well As Deactivation Mechanisms Of Catalyst

Photocatalytic oxidation as a kind of cheap,efficient,small secondary pollution depth of water treatment technology,in the domestic and industrial wastewater and drinking water treatment research,there are a lot of research involving efficient catalyst development and modification,pollutant removal mechanism,photocatalytic treatment efficiency of influencing factors,etc.Powder photocatalysts are usually used in the above studies and are mainly used in short-term,single catalytic experiments.However,in practical industrial applications,catalysts need to have a variety of practical characteristics such as high activity,long life,low cost,easy recovery,etc.Therefore,researchers began to pay attention to the cycle life of photocatalysts.However,we still have a limited understanding of the factors influencing catalyst activity in different reaction environments and the mechanism of deactivation,which is the key research basis for regulating reaction conditions to delay catalyst deactivation and developing durable photocatalysts.Therefore,in this paper,the treatment of medical wastewater prepared in laboratory as the background,using nickel foamed Ti O₂（Ti O₂/NF）as photocatalyst,5-fluorouracil（5-FU）as the target drug micropollutant,escherichia coli（E.coli）as the target bacteria;A 130-hour cyclic photocatalytic water treatment experiment was carried out in a continuous flow photocatalytic reactor to explore the long-term cyclic photocatalytic removal effect of single drug（5-FU）and drug-microbial mixture（5-FU+E.coli）in simulated actual water,and its influence mechanism on the activity of Ti O₂/NF immobilized photocatalyst.It was found that cyclic photocatalysis was carried out in 5-FU single component solution.If fixed Ti O₂ was used continuously throughout the whole process,the 5-FU removal rate decreased slowly from 91.4%to 17.2%after 130 hours of cycle experiment.On the contrary,if fixed Ti O₂ was dried after each experiment and the shed Ti O₂ was removed,the 5-FU removal rate dropped from 82.3%cliff to 25.5%after two cycles of experiment,and gradually decreased to 5.8%.All these results indicate that the fixed photocatalyst has been deactivated.In this paper,the degradation products of 5-FU were analyzed qualitatively and semi-quantitatively by UPLC-Q Orbitrap-MS.The surface morphology,elemental composition and characteristic functional groups of fixed Ti O₂ photocatalyst were characterized by SEM-EDS and ATR-FTIR,and the gradient experiments content of F^-and solution p H were carried out.The results showed that 5-FU degradation intermediates accumulated in solution or on the surface of the photocatalyst and competed with 5-FU for·OH and inhibit the photocatalytic removal of the target drug.Considering the complexity of the actual wastewater components,the content of pathogenic bacteria is also an important index of water quality control in addition to drug micropollutants.In order to further explore the cause of catalyst deactivation in the photocatalytic treatment of medical wastewater by immobilized Ti O₂,the combined photocatalytic treatment experiment was carried out in the mixed solution of 5-FU and E.coli.After 130 hours of cyclic photocatalytic experiment,the removal efficiency of 5-FU was reduced from 53.0%to 6.3%,and the illumination time required for complete inactivation of Escherichia coli（inactivation rate>99.99%）was extended from 4h to 6h,indicating that the immobilized Ti O₂ was almost completely inactivated during long-term use.In addition,the coexistence between target also have an adverse effect:normal saline in the Cl^-can be combined and^·OH and translated into oxidation ability weaker^·Cl,and highly fragmented Escherichia coli in the salt water will be part of the incident light absorption and scattering,lead to the combination of 5-FU photocatalytic removal efficiency is lower,and 5-FU inactivated no adverse effect on E.coli.Furthermore,the light absorption characteristics,surface morphology and photochemical properties of immobilized Ti O₂ before and after deactivation were characterized by UV-vis DRS,HR-SEM and electrochemical workstation（transient photocurrent response）.The results showed that the surface of the deactivated Ti O₂catalyst was almost completely covered by the biofilm formed by the deactivated Escherichia coli residues,which hindered the adsorption of H₂O,O₂ and other molecules on the surface of Ti O₂,resulting in the decrease of free radical yield and the inhibition of the removal of target pollutants.