Study On Preparation Modification Of Graphite Phase Carbon Nitride And Photocatalytic Degradation Of Tetracycline In Water

Semiconductor photocatalysts can use solar energy to produce new energy and degrade pollutants,and show great potential in solving global resource shortages and environmental pollution problems.Carbon nitride photocatalysts have become a research hotspot in recent years due to their low price,high stability,and environmental friendliness.However,carbon nitride as a photocatalyst currently has some problems,such as prone to agglomeration,excessively wide band gap,and low quantum efficiency.Therefore,it is necessary to optimize the preparation method of carbon nitride,improve the agglomeration phenomenon of carbon nitride,and modify it through methods such as element doping and semiconductor compounding to improve the photocatalytic reaction performance of the catalyst.In this paper,melamine and nitric acid are used as raw materials to synthesize graphite phase carbon nitride(g-C3N4)by thermal polymerization.The agglomeration problem of carbon nitride was solved by stripping the massive carbon nitride into lamellar carbon nitride by controlling the reaction temperature.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),specific surface area(BET),X-ray diffraction(XRD),Fourier infrared spectroscopy(FT-IR),X-ray diffraction(XRD)analysis,UV-visible diffuse reflectance spectroscopy(UV-Vis)were used DRS and PL were used to characterize the catalysts prepared at different calcination temperatures.The g-C3N4 sample prepared at 550℃ has the most complete lamellar structure,the strongest visible light absorption capacity,and the degradation efficiency of TC after 50 min of light is 43.0%.In order to improve the photocatalytic performance of the photocatalyst,g-C3N4 is doped and modified with B element and Eu element.B-doped carbon nitride(B-CN),Eu-doped carbon nitride(Eu-CN),and B and Eu co-doped carbon nitride(B/Eu-CN)were synthesized by thermal polymerization sample.The effects of elemental doping on the morphology,lattice and specific surface area of the catalyst were investigated by a series of characterization methods.Compared with the single-doped sample,the B/Eu-CN sample has a uniform mesoporous structure and the largest specific surface area,which is about twice that of pure CN.Co-doping of B/Eu elements introduces impurity levels in the energy level structure of the original carbon nitride.The forbidden band width of carbon nitride is effectively reduced,the distance of electronic transition is shortened,and the ability of photocatalytic degradation of TC is improved,and the degradation efficiency of TC reaches 90.8%after 50 min of light.In order to further improve the photocatalytic performance of the photocatalyst,molybdenum disulfide(MoS2)with a narrower band gap and carbon nitride-based catalyst are used for compound modification.Using ammonium molybdate tetrahydrate and thiourea as precursors,MoS2 was prepared by hydrothermal synthesis using ammonium molybdate tetrahydrate and thiourea as precursors,and then composited with a carbon nitride-based catalyst by the ultrasonic dispersion method to synthesize MS/CN and MS/B/Eu-CN samples.The direct Z-type heterojunction between MoS2 and carbon nitride catalyst was confirmed by SEM,TEM,FT-IR and XPS.The direct Z heterojunction optimizes the migration path of photogenerated carriers and speeds up the separation of photogenerated electrons and holes.Compared with other catalysts,MS/B/Eu-CN has the strongest visible light absorption capacity and the best catalytic effect.The reaction rate constant k value of MS/B/Eu-CN for TC degradation is 1.8 times that of B/Eu-CN.According to the test results of total organic carbon,MS/B/EU-CN degrades TC more thoroughly.·O2-was confirmed to be the main active substance in the catalytic system by free radical quenching test.