Preparation Of BiPO₄ Composites Photocatalyst And The Application Of Photocatalytic Degradation Of Tetracycline

With the rapid development of society,people's medical level continues to rise,and the application of antibiotics is becoming more and more common.Especially in recent years,the abuse of tetracycline antibiotics has become more and more serious,and the content of tetracycline in natural water can often be detected exceeding the standard.Traditional treatment methods of tetracycline antibiotics have various defects.The photocatalytic technology developed by using semiconductor materials is a new green and environmentally friendly water pollution treatment technology,which has been widely applied to the treatment of organic pollutants in water.Among many semiconductor photocatalysts.Bismuth phosphate?BiPO₄?is considered to be a very stable and efficient semiconductor photocatalyst material.BiPO₄ has good application prospects in photocatalytic degradation of organic pollutants in water.However,the wide band gap of BiPO₄ and the easy recombination of photogenerated electron holes hinder its application in the direction of photocatalysis.In this paper,rod-like BiPO₄ is prepared by solvothermal method,BiPO₄ and narrow bandgap indium sulfide?In₂S₃?are compounded to obtain In₂S₃/BiPO₄ heterojunction photocatalysts.Then the Ag/In₂S₃/BiPO₄ ternary composite photocatalysts are prepared by photodeposition of precious metal Ag on the surface of the composite.In addition,Fe?III?doped BiPO₄ was modified to obtain Fe?III?doped BiPO₄ composite photocatalyst,and then carbon quantum dots are loaded to Fe?III?doped.CDs/Fe-BiPO₄ ternary composite photocatalysts are prepared on BiPO₄.The main research contents are as follows:?1?In₂S₃/BiPO₄ heterojunction photocatalysts are successfully synthesized by solvothermal method.When the mass fraction of BiPO₄ in the composite is 15.0%,the composites have the best visible-light degradation activity for tetracycline,and nearly 71.4%tetracycline is degraded within 100 min.It is found that the enhancement of photocatalytic activity is due to the more efficient photogenerated electron hole separation efficiency of In₂S₃/BiPO₄ heterojunction composite photocatalyst.The photocurrent strength of the composites is almost twice that of the monomer In₂S₃,and the fluorescence intensity of the composites is much lower than that of the pure In₂S₃.Subsequently,the valence band positions of In₂S₃ and BiPO₄ are discussed accurately by means of UV-Vis diffuse reflectance spectra and valence band spectra.The samples are captured and characterized by ESR.The results show that superoxide radicals and holes are the main active substances in the photodegradation process of the composite photocatalyst.?2?Ag is loaded on the surface of In₂S₃/BiPO₄ heterojunction composite photocatalyst by photodeposition method,and the amount of silver nitrate solution is adjusted to obtain different Ag loaded composite photocatalysts.The visible light absorption of Ag/In₂S₃/BiPO₄composite photocatalysts are higher than that of In₂S₃/BiPO₄ heterojunction photocatalyst by UV-visible diffuse reflectance spectroscopy.This may be due to the plasma resonance effect of Ag nanoparticles.The Ag/In₂S₃/BiPO₄ composite photocatalysts are then tested by fluorescence and photoelectrochemistry to show that Ag/In₂S₃/BiPO₄ composite photocatalysts have a more efficient separation efficiency of photogenerated electron holes,which may be due to its good conductivity,which could promote the separation of photogenerated electron holes.The photocatalytic activity of the composites are tested.The results show that the composite exhibited the best degradation activity when Ag content is1.0%,and the degradation rate reach to 85.1%within 100 min.?3?BiPO₄ composite photocatalysts doped with Fe?III?are synthesized by one-step solvothermal method.The results of XRD,Raman,SEM and XPS tests showed that BiPO₄composite photocatalysts doped with Fe?III?are successfully synthesized.The samples are characterized by UV-Vis diffuse reflectance spectroscopy,valence band spectroscopy,fluorescence and photoelectrochemical characterization.The results show that the band gap of BiPO₄ doped with Fe?III?is obviously reduced and the photoabsorption is improved.The range of photocatalytic activity is increased,and the photogenerated electron hole separation was more efficient,so the photocatalytic activity is enhanced.When the molar fraction of Fe?III?doping is 5.0%,the degradation of tetracycline reaches the maximum of 66.2%in 100min under simulated sunlight.Finally,the mechanism of photocatalytic reaction of BiPO₄photocatalyst doped with Fe?III?is discussed.It is found that Fe?III?could capture electrons and improve the separation efficiency of photogenerated electrons and holes.?4?The carbon quantum dots are compounded with Fe?III?-doped BiPO₄ composite photocatalyst.Fluorescence measurements show that carbon quantum dots have excellent upconversion photoluminescence properties.The optimum loading ratio was found to be 3.0%of the total composite.The degradation rate of tetracycline reach to 89.8%in 100 min under simulated sunlight.Moreover,the photocurrent intensity of the optimum loading ratio is significantly higher than that of pure BiPO₄ and Fe?III?doped BiPO₄,which indicates that the composite exhibits higher electron hole separation efficiency after loading carbon quantum dots.The capture experiments of active species show that the holes were the main active substances in the photodegradation process of the composite photocatalyst.