Study On The Performance And Mechanism Of Degradation Of Tetracycline Hydrochloride By FeS₂/g-C₃N₄

Tetracycline（TC）is the second most commonly used antibiotic in the world,and its residual in water caused widespread concern,which has severely affected the ecological environment and human health.Among the traditional treatments,the biological toxicity of tetracycline decrease the degradation efficiency of biochemical method,the removal rate of anaerobic biochemical pretreatment is about 45%.The removal rate of physical method like adsorptine could reach 90%-100%,which has not achieved the decomposition of tetracycline.Therefore,photocatalytic has a good application prospect in the treatment of TC.Among the new semiconductors,graphite phase carbon nitride（g-C₃N₄）has moderate band gap（2.70 eV）,good thermal stability,chemical stability and environmentally friendly.FeS₂,a tipical of transition metal dihalides,has the band gap of 0.95 eV,high absorbance(α=6×10⁵ cm^-1),good electrochemical,optical and magnetic characteristics.The combination of FeS₂ and g-C₃N₄ to prepare heterojunction materials could improve the absorbance of light,expand the light absorption range,limit the recombination of photogenerated electron holes in g-C₃N₄ and the agglomeration of FeS₂ in solution.Finally,it could realize the efficient removal of tetracycline hydrochloride（TCH）under visible light.In this study,FeS₂ was prepared by hydrothermal method,g-C₃N₄ was prepared by high temperature calcination method,and FeS₂/g-C₃N₄ heterojunction materials were composited by ultrasonic bath and high temperature calcination method.It provides a new type of catalyst for antibiotic wastewater treatment and promotes its application in the field of water treatment.The composition structure and morphology were analyzed by X-ray diffraction spectroscopy（XRD）,scanning electron microscopy（SEM）,X-ray energy spectroscopy（EDS）,fourier transform infrared spectroscopy（FT-IR）,and X-ray photoelectron spectroscopy（XPS）.The optical properties of composites were studied by diffuse reflection spectrum（DRS）,photoluminescence spectrum（PL）,and photocurrent response curve（I-t curve）.20%FeS₂/g-C₃N₄ was selected as photocatalyst by comparing the degradation rate,preparation costs and metal dissolution of different proportions of composite materials.Moreover,a 20%FeS₂/g-C₃N₄/H₂O₂ system was established to degrade TCH and identified the reactive oxygen species,TOC degradation,GC-MS analysis,E.coli bacteriostasis,XRD and XPS analysis on repeated materials to explore the degradation mechanism,degradation products and toxicity of intermediate products.The effects of catalyst dosage,oxidant dosage and illumination were studied to optimize the process parameters of the 20%FeS₂/g-C₃N₄/H₂O₂ system.The practical applicability of the 20%FeS₂/g-C₃N₄/H₂O₂ system was investigated by studying the effects of initial pH,temperature,inorganic anions and natural organic matter in water.The FeS₂/g-C₃N₄ composite material is type Ⅰ heterojunction material,which is conducive to enhancing the absorbance of g-C₃N₄,reducing the photo-generated electron-hole recombination rate and improving the dispersion of FeS₂ in solution.Using 0.50 g/L 20%FeS₂/g-C₃N₄ and 50.0 mM H₂O₂ to establish a20%FeS₂/g-C₃N₄/H₂O₂ system under 50 W visible light（T=25°C）to degrade 0.05 g/L TCH solution.The removal of TCH in 30 minutes was 87.0%,which was 9.56 times that of g-C₃N₄,1.15 times that of FeS₂ and 1.11 times under dark condition.The effect of the type I heterojunction and the Schottky barrier could prolong the carrier lifetime.The photo-generated electrons（e^-）,holes（h⁺）,together with hydroxyl radical（·OH）,singlet oxygen（¹O₂）and superoxide anion(O₂^·-)complete the degradation of TCH,among which·OH is the dominant active species with the contribution rate of 61.43%.The benzene ring structure in TCH opened and the central carbon chain cleaved.The mineralization rate reaches 42.5%in 60 minutes,and the toxicity of degradation products is significantly reduced.The reaction activation energy is 28.24 k J/mol and has a wide range of p H.The system could be less affected by inorganic anions and natural organic matter in water.The degradation of TCH by the 20%FeS₂/g-C₃N₄/H₂O₂ system has not been seriously affected by the complex environment in actual water and has a good degradation effect of methyl orange and bisphenol A.FeS₂/g-C₃N₄ composites are easy to be prepared and the cost during preparation are low.FeS₂/g-C₃N₄ composites can achieve efficient degradation of organic pollutants in water in a short time.FeS₂/g-C₃N₄ composites have good photocatalytic efficiency in complex water environment and a certain broad spectrum,which are prospected to be used in the field of sewage treatment.