Preparation And Photocatalytic Dye Degradation Of Ag₃PO₄-modified Photocatalysts

Water is indispensable to life precious resources,and the water has an irreplaceable role in maintaining human survival,safeguarding the economic construction and promoting social development.However,the pollution of water resources has caused serious threat to people's survival and development,and the environmental and social problems caused by water pollution are increasingly prominent,therefore water pollution control must be settled urgently.Because of the complex composition and high chroma of dye wastewater,it is difficult to treat it by traditional methods.Using green photocatalytic technology to deal with dye wastewater has the advantages of strong purification ability and no secondary pollution,so it is of great significance to develop photocatalytic technology to degrade dye wastewater efficiently.Silver phosphate photocatalyst has high quantum efficiency and photocatalytic degradation activity,but it is unstable under light and prone to photocorrosion,which severely limits the application of silver phosphate photocatalyst in the field of photocatalysis.Aiming at the current photocorrosion problems of silver phosphate photocatalyst,in this thesis there prepared Ag₃PO₄photocatalyst and Ag₃PO₄/GO photocatalyst,respectively,using p-hydroxy benzoic acid as the organic ligand and structure control agent by ways of ion exchange and low temperature liquid phase precipitation method.Actors affecting the photocatalytic dye degradation of Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst such as synthesis conditions and photocatalytic conditions were investigated.The recycling performance of Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst were also studied.Structure and morphology of Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst were characterized by means of XRD?X-ray diffraction?,FESEM?Field emission scanning electron microscopy?,diffuse UV-Vis,FTIR?Fourier infrared spectroscopy?,XPS?X-ray electron spectroscopy?,Raman and AFM?Atomic Force Microscope?.Photocatalytic degradation mechanism of Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst were also discussed.The main research work are as follows:1.The optimal synthesis conditions of silver phosphate photocatalyst were as follows:silver nitrate/organic acid molar ratio of 1:1,silver nitrate/sodium dihydrogen phosphate molar ratio of 1:1.3,reaction p H of 4 and reaction time of 2h.The photocatalytic dye degradation of silver phosphate photocatalyst reached 97.1%after4min LED illumination.The optimal synthesis conditions of Ag₃PO₄/GO photocatalyst were as follows:GO amount was 1%,the molar of silver nitrate/organic acid of 1:1,the reaction time of 2h,and the reaction p H of 5.Photocatalytic dye degradation by Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst was 97.1%and97.8%,respectively under LED illumination.When the initial concentration of methyl orange dye was 10mg/L and 30mg/L respectively,the photocatalytic degradation of methyl orange dye by silver phosphate photocatalyst and Ag₃PO₄/GO photocatalyst under 4min LED illumination were 97.1%,69.2%and 97.8%,74.1%,respectively.When the amount of photocatalyst is 1g/L,both silver phosphate photocatalyst and Ag₃PO₄/GO photocatalyst have the best photocatalytic dye degradation performance.2.The photocatalytic dye degradation by Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst were in accordance with quasi-first-order kinetics,in which the rate constant k was 0.687 and 0.708 min^-1 and the correlation coefficient R² was 0.9878and 0.9801 respectively.Photocatalytic dye degradation of Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst were 71.1%and 75.8%respectively after 5 times recycling.Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst have energy gaps of 2.26e V and2.16e V,and absorption edges of 548nm and 574nm,respectively.3.XRD and FTIR indicate that Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst have target structure.XPS indicates that both Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst have target element composition,element oxidation state and molecular structure.FESEM shows that Ag₃PO₄ photocatalyst has a tetrahedral structure with a particle size of 0.2-2.0?m and a porous structure.Reaction in the condition of p H=4 is favorable for the formation of tetrahedral silver phosphate photocatalyst.With the increasing alkalinity of the solution,the form of silver phosphate gradually changed from tetrahedral to spherical shape.Ag₃PO₄/GO photocatalyst has a tetrahedral structure silver phosphate,and GO is tightly coated on the surface of silver phosphate in sheet form.FESEM and AFM indicate that GO has a flake structure,and Raman spectroscopy indicates that the Ag₃PO₄/GO photocatalyst contains GO components.4.Both Ag₃PO₄ photocatalyst and Ag₃PO₄/GO photocatalyst have the main active species of superoxide radical?·O₂^-?and hole?h⁺?during photocatalytic dye degradation,while hydroxyl radical contribution is small.The contribution order is h⁺>·O₂^->·OH.