The Synthesis And Photocatalytic Properties Of Ag-Ag₂S/g-C₃N₄ Nanosheets

Since the nineteenth century,the increasing global population and the rapid development in various fields have brought the industrialization of the entire society to a higher level.The overuse of fossil resources and the excessive expansion of biomedicine cause a great deal of damage to the natural environment.For the sustainable development of mankind,it is urgent to find a stable and green way to solve the existing energy shortage and environmental pollution.The photocatalytic technology of semiconductors has attracted extensive attention in recent years,which has a series of unique advantages such as less pollution,stable physical and chemical properties,simple operation and low manufacturing cost,and is a environmentally friendly,energy-saving and sustainable technology.In terms of metal-free semiconductor materials,g-C₃N₄with good chemical stability,mechanical stability,thermal stability and a suitable band gap(2.7 e V)has already caused widespread scientific interest in the field of photocatalysis.So far,g-C₃N₄has gotten good application in the degradation of organic pollutants,hydrogen production,and carbon dioxide emission reduction.The paper is to use ethanol as a solvent and melamine as precursor,to synthesize the ultrathin carbon nitride nanosheets(UCN)by thermal polymerization method,originally to build a heterojunction containing Ag-Ag₂S(denoted as Ag CN)by the in-situ growth method.The main target pollutant for testing the properties of the prepared photocatalysis in the subject is tetracycline(TET).In the project,supramolecules formed of cyanuric acid and melamine were used as precursors to form an aerogel state through freeze-drying,and then carbon nitride aerogel(CNA)was synthesized by thermal polymerization,and Ag-Ag₂S was loaded to form a composite material,denoted as Ag CNA.The photocatalytic degradation efficiency of TET was tested and optimized.The chemical structure and optical properties of the material were characterized in the subject,including scanning electron microscopy(SEM),transmission electron microscopy(TEM),x-ray electron energy spectroscopy(XPS),energy spectroscopy(EDX),and x-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FT-IR),Ultraviolet-Visible Diffuse Reflectance Spectroscopy(UV-vis DRS),Photoluminescence(PL)technology,Photocurrent response(PR)and Electrochemical Impedance Spectroscopy(EIS)analysis.The photocatalytic experiment under visible light of the material was carried out with a 300 W xenon lamp.The concentration of the pollutant after the reaction was measured by an ultraviolet spectrophotometer.The effect of different p H on the degradation ability of photocatalytic materials was discussed.Free radicals capture experiment and Electron spin resonance spectroscopy(ESR)analysis were used to discuss the major free radicals in the photodegradation system,and finally study the possible mechanism of degradation of organic pollutants.The project firstly optimized the synthesis conditions of CNA,and then optimized the loading of Ag-Ag₂S.The results showed that the optimized ratio of Ag-Ag₂S to UCN and CNA is 10%.Under visible light irradiation,Ag CN and Ag CNA have excellent photocatalytic degradation ability of TET.Compared with the original g-C₃N₄,the degradation efficiency of Ag CN and Ag CNA can reach 90.4%and 95.1%respectively,which are 3.6 and 3.8 times the original g-C₃N₄material(26%).Then the project also compared the degradation effect of Ag CNA-10%on TET and Rhodamine B,which showed better degradation performance on dye.By measuring the degradation performance and crystal structure of Ag CN-10%and Ag CNA-10%materials after four cycles,it was found that the materials have good cycle stability.The project also studied the effect of the initial pollutant concentration and the initial p H value on the photocatalytic effect,it was found that when the TET concentration is low,the photocatalytic degradation ability of the two materials is higher,and the Ag CNA-10%catalytic effect is stronger when the p H is weak.This is because Ag CNA samples possessed higher specific surface area,more reaction contact surfaces and wider light absorption range.In addition,the doping of Ag and Ag₂S increases the active sites of the material and increases the separation efficiency of photogenerated carries.The free radical trapping experiment and electron spin resonance test proved that the main active species are h⁺,·O₂^-and·OH.However,the main active substances in Ag CNA-10%are h⁺and·O₂^-,while the secondary active substance is·OH.