Preparation Of Ag₂S-Bi₂WO₆ And Its Photocatalytic Degradation Of Antibiotics

The abuse of antibiotics has caused increasingly serious environmental problems,its strong persistence,biological activity and ecological toxicity can directly threaten human health through the food chain,how to treat antibiotic wastewater has become a focus of domestic scholars.At present,the common antibiotic wastewater treatment methods include chemical method,physical method,biodegradation method and advanced oxidation method.As one of the advanced oxidation methods,photocatalytic oxidation technology is considered to be an ideal method to treat antibiotic wastewater because of its advantages of energy saving and environment friendly.Bi₂WO₆has the characteristics of stable crystal structure,narrow forbidden bandwidth and good photocatalytic activity,which has attracted extensive attention of researchers in the fields of photocatalysis,new materials and energy conversion,and has become one of the new visible photocatalysts with great research prospects.However,pure phase Bi₂WO₆has limitations such as high photogenerated electron-hole recombination rate,low active site and slow charge transfer rate,which seriously hinder its application in industrialization and industrialization.Based on the above problems,this paper does not add any auxiliary agent and in neutral conditions with ultrapure water as solvent,was prepared by different water thermal conditions with different morphology and phase photocatalytic performance of pure Bi₂WO₆,XRD,SEM,UV-vis characterization methods and light catalytic degradation experiments,it is concluded that water dicating 12h,the reaction condition control in the 200℃can preparation the photocatalytic performance good3D flower Bi₂WO₆.Ag₂S was modified on the three-dimensional flower-like Bi₂WO₆surface by in-situ deposition method,and the composite catalysts with mass ratios of3%,7%and 11%were prepared.XRD,SEM,XPS,EDS and UV-vis were used to characterize the crystallinity,morphology,binding mode,elemental composition and optical properties of the samples.The results show that the Ag₂S-Bi₂WO₆composite catalyst has good dispersivity,crystallinity and purity,and the two materials are closely bonded by chemical energy.At the same time,when the mass ratio is 7%,the composite catalyst has the best light absorption intensity and absorption range.Using Ag₂S-Bi₂WO₆as photocatalyst,doxycycline hydrochloride and tetracycline hydrochloride as target pollutants,the photocatalytic degradation experiments were carried out.The photocatalytic performance of the composite catalysts with different mass ratios was investigated.The effects of the dosage of the composite catalyst,the initial concentration of pollutants,the initial p H of the solution,the concentration of humic acid and different inorganic anions on the degradation efficiency were also discussed.The stability of the composite catalyst was discussed by the repeatability experiment.The main active substances and mechanism in the photocatalytic reaction were analyzed by the free radical capture experiment and the semiconductor energy band theory,and the degradation pathway of the target pollutants was prelimarily speculated by the mass spectrometry characterization method.The results show that 7%Ag₂S-Bi₂WO₆composite catalyst has the best degradation effect on the two kinds of target pollutants.With the increase of the dosage of composite catalyst,the degradation rate of the target pollutants increases.When the initial concentration of the target pollutant increases,the degradation rate decreases.When the initial p H value of the solution increases from 3 to 11,the removal of target pollutants increases firstly and then decreases.When the p H is acidic,the photocatalytic efficiency will be severely inhibited.Humic acid had little effect on the photocatalytic degradation of doxycycline hydrochloride,but could inhibit the degradation efficiency of tetracycline hydrochloride.The inorganic anions CO₃^2-and HCO₃^-promoted the degradation rate of the target pollutants,NO₃^-reduced the degradation rate,and Cl^-mainly affected the adsorption efficiency of the composite catalyst for the target pollutants.At the same time,the 7%Ag₂S-Bi₂WO₆composite catalyst was repeated for five times,which showed that it had excellent stability.In the free radical capture experiment,hydroxyl radical（·OH）and superoxide radical（·O₂^-）were the secondary active substances in this experiment,and photogenerated hole（H⁺）was the main active substances.Under the action of light and h⁺,the target pollutants are mainly decompose through the removal of-N-CH₃,-NH,-C-OH,-CONH₂and other groups.As the reaction continues,the intermediate will eventually be degraded into small inorganic molecules such as CO₂,H₂O,NH⁺.