Study On Synthesis Of Carbon Nitride Based Photocatalytic Materials And Photocatalytic Degradation Of Antibiotic In Water

Photocatalysis technology,one of the ideal technologies to solve energy shortage and environmental pollution by converting solar energy to chemical energy,is of great significance to the sustainable development of human society.Graphitic carbon nitride（g-C₃N₄）has facile preparation method,high stability and attractive visible light response ability.The bulk g-C₃N₄ prepared by thermal polymerization has small specific surface area,inferior dispersion,dense surface defects,rapid recombination velocity of electrons and holes,which severely represses the photocatalytic activity of g-C₃N₄.In order to enhance the photocatalytic activity of g-C₃N₄,some methods are used to modify it,such as modulating the structure of energy band,enlarging the specific surface area,preparing heterojunctions.In order to increase the ratio surface area of g-C₃N₄ and extend the absorption range of visible light,nitric acid and samarium nitrate were used to modifiy the g-C₃N₄ and Sm doped mesoporous g-C₃N₄（SCN）catalysts were prepared.The morphologies,elemental composition,photon-generated carrier separation efficiency,specific surface area and light adsorption ability were inves tigated in details.The photocatalytic activity was evaluated with the degradation effect of rhodamine B（Rh B）and tylosin（TYL）,and the photodegradation results showed that the SCN sample owns good photocatalytic activity when the addition of samarium nitrate is 0.025%（mol/mol）.Seed germination experiments,escherichia coli inhibition experiments and degradation cycle experiments were carried out to verify the safety and stability of SCN catalsts in water.The possible photocatalytic mechanism of SCN catalyst was deduced based on the results of characterization and ree radical capture experiments.In addition,the effects of initial TYL concentration,solution p H,aeration rate,common anions in water and illumination intensity on photocatalytic degradation of TYL were investigated.In order to thoroughly investigate the modification impact of other rare earth ions for g-C₃N₄,Er doped mesoporous g-C₃N₄（ECN）catalyst was prepared by acid treatment and element doping.Approaches such as TEM,FT-IR,solid nuclear magnetic,XPS,PL and photoelectrochemical detection were exercised to characterize the physicochemical properties of as-prepared ECN catalysts.The Rh B photodegradation experiment was used to evaluate the photocatalytic performance of ECN catalysts.The results showed that the ECN-0.05 cataltst maintained the best photocatalytic activity when the doping amount of erbium nitrate was 0.05%（mol/mol）.The safety and stability of ECN catalysts in water environment were evaluted by seed germination experiments,Escherichia coli inhibition experiments and degradation cycle experiments.The versatility of antibiotic potodegradation over ECN catalysts was detected by degradation of tetracycline（TC）and TYL.In addition,Yb and Er codoped mesoporous g-C₃N₄ catalysts（YECN）were prepared and characterized.The YECN catalyst has the optimal photocatalytic activity when the addition of erbium nitrate and ytterbium nitrate was 0.05%（mol/mol）and 0.015%（mol/mol）,respectively.In order to enhance the photo-induced carrier separation efficiency,g-C₃N₄/Ag/GO（CNAG）heterojunctions were prepared by the methods of photodecomposition and ultrasound assisted which load the noble metal Ag nanoparticles and GO on the surface of g-C₃N₄.The load parameters were optimized:the addition of GO was 6 wt%and photodeposition time was 15 min.A series of characterizations,such as TEM,PL and photochemical tests,were employed to characterize CNAG samples.The Ag nanoparticles load on the surface of g-C₃N₄ with high dispersity.With the addition of Ag and GO,the separation efficiency of photo-induced carrier was significantly increased,improving the photocatalytic performance of g-C₃N₄.The safety and stability of CNAG photocatalyst in water were evaluated by seed germination test and degradation cycle test,respectively.The possible photocatalytic degradation mechanism was deduced.In order to further improve the photocatalytic activity,CdS with narrow bandgap was coupled with g-C₃N₄ to prepare and characterize direct Z-type g-C₃N₄/CdS（CNCS）heterojunction.Compared with g-C₃N₄,the addition of CdS in CNCS samples greatly increased the absorption range,enhanced the intensity of visible light and improved the separation and migration rate of photo-induced carriers.The results of Rh B and TC photodegradation showed that the CNCS-0.25had the best photocatalytic activity when the addition of CdS was 25 wt%.The photodegradation mechanism of CNCS composite was proposed based on the results of experiments and characterization.Furthermore,the Yb/Er/g-C₃N₄/CdS（YECNCS）photocatalyst was synthesized by combination of CdS and mesoporous YECN-0.015.The experimental results of Rh B and TC degradation showed that YECNCS catalyst had excellent photocatalytic ability to degrade organic pollutants.