Application Of Modified Nitride On The Degradation Of Tetracyline Antibiotics In Water Environment

As antibacterial and growth-promoting agents,antibiotics have been widely used in human clinical and veterinary medicine.With the increasing number and expanding role of antibiotics,people's dependence on antibiotics has became stronger and the abuse of antibiotics more serious.The extensive used antibiotics eventually enters into the environment,causing potential environmental pollution and threatening human'health.Tetracyclines?TCs?are one of the most widely used antibiotics in the world due to their broad-spectrum antibacterial activity,remarkable efficiency,and low price.They have a half-life of 7 days in neutral aqueous solutions and up to 44 days in acidic conditions.Because of its broad-spectrum antibacterial properties,conventional biological treatments have certain limitations.Therefore,it's necessary to explore efficient,inexpensive,and green photocatalytic oxidation remediation materials under natural light conditions to reduce or eliminate the environmental risks caused by such substances.Among the semiconductor photocatalytic materials,graphite-phase carbon nitrite?g-C₃N₄?can be excited by visible light due to its narrow band gap,which has become the current research direction for exploring novel visible light-responsive photocatalytic materials.Accordingly,in this dissertation,using Tetracycline Hydrochloride?TC-HCl?as the target contaminant,we explored the feasibility of preparing high efficient catalysts under visible light by using transition metal ions such as Cu and WO₃ to co-modified g-C₃N₄ and determined the optimal preparation and modification conditions.And then,the degradation influence factors and mechanisms by powder Cu-g-C₃N₄/WO₃ catalyst have been studied.At the same time,the powder catalyst was loaded on the granular carrier under the optimized loading conditions and applied to a full-mixed photocatalytic reactor,simulating the ectopic control of Tetracycline-containing water and exploring the factors of the reactor and the stability of the supported catalyst.Finally,the degradation pathways of TC-HCl during the photocatalytic degradation have been studied.The corresponding research results are as follows:?1?Preparation of modified g-C₃N₄ and photocatalytic degradation of TC-HCl.The g-C₃N₄ catalyst was prepared by calcination on the optimized preparation conditions.On this basis,transition metal ion?Cu,Mn,Fe?doping and WO₃ modification were carried out.The optimal preparation and modification conditions were confirmed by XRD,SEM,UV-Vis and PL characterization and degradation experiments.The best conditions are calcined by urea at550?and modified with 0.16%molar ratio Cu ions and 5%mass ratio WO₃.Degrading the TC-HCl solution using this powdery catalyst and LED white light as the visible light source,it was found that the larger amount of added catalyst and the smaller initial concentration of the substrate,the faster tetracycline degradation rate and the optimal pH is 5.The reaction rate increased from 0.01003 min^-1 to 0.02986 min^-1 and the half-life shortened to 23.31 min..Through the study of characterization and degradation mechanism,it was found that the transition metal ions doped into the interior of the crystal and changed the surface morphology of g-C₃N₄,increased the specific surface area,narrowed the band gap and inhibited the recombination probability of electrons and holes.Meanwhile,a Z-type heterostructure was formed by coupling WO₃ with Cu-g-C₃N₄,so that the separation efficiency of photogenerated electrons and holes were improved.The photocatalytic active groups were changed from·O₂^-to holes,·O₂^--,and·OH^-.?2?Immobilization of Cu-g-C₃N₄/WO₃ catalyst and its application in photocatalytic reactor.The Cu-g-C₃N₄/WO₃ catalyst was immobilized on silica gel particles by adding PVB adhesive to the solution.The optimum preparation conditions were confirmed:the mass ratio of added PVB was 2.5%,the mass ratio of catalyst to the silica gel was 0.01875:1,and the drying temperature of the loaded solution was 100?.Applied the silica gel-loaded Cu-g-C₃N₄/WO₃ catalyst into a fully-mixed reactor using LED white light?18000 lux?as visible light source,the TC-HCl removal up to 90%in 240 min.The degeration conditions were confirmed:the catalyst dosing was 60 g/L,the initial TC-HCl concentration was 20mg/L,aeration rate was 0.5 L/min.Changing the type and intensity of light can further improve the degradation rate.After 4 times repeated using,the catalytic performance dropped about 10%and the catalyst recovery rate was around 75%.?3?Determination of tetracycline degradation processes and intermediate products.The main degradation pathways and intermediate products of tetracycline were inferred by HPLC-MS testing.After photocatalytic degradation,many intermediate products were produced.The substitution of·OH,the addition of double bonds,and the removal of-CONH₂,NH₃,-CH₃,and--N?CH₃?₂ groups have mainly taken place.The product has been finally oxidized and opened and degraded into small molecules such as CO₂ and H₂O.