Study On The Preparation Of Silver Phosphate Based Composites And Their Photocatalytic Degradation For Organic Pollutant

Photocatalytic technology,as an environmentally friendly advanced oxidation technology that has gradually emerged in recent years,has attracted much attention in the energy and environmental fields.The core of photocatalytic technology is the development of visible light-responsive semiconductor materials.As a new visible light catalyst,silver phosphate（Ag₃PO₄）has attracted much attention because of its strong advantages in the photocatalytic water oxidation and degradation of organic matter.However,the characteristics of Ag₃PO₄ micro-dissolution water and severe photocorrosion have caused its poor stability,which greatly limits its practical application.Therefore,the purpose of this thesis is to improve the photocatalytic activity and stability of Ag₃PO₄ in the degradation of organic pollutants.Based on the basic principles of photocatalysis,the band theory,and the mechanism of electron（e^-）-hole（h⁺）migration and conversion,a series of Ag₃PO₄-based composites were reasonably constructed.Through a series of characterization testing methods,the morphology,crystal structure and photoelectricity properties of the synthesized catalyst were characterized in detail.The synthesized catalyst was applied to the photocatalytic degradation of organic substances.The electron transfer mechanism,photocatalytic degradation mechanism and anti-photocorrosion mechanism of the photocatalytic system were studied in detail.The main research results are as follows:（1）Preparation of Ag₃PO₄@RGO@La,Cr:SrTiO₃ and the performance and mechanism of photocatalytic degradation of organic pollutants.Graphene oxide（GO）was prepared by an improved Hummers method,and Ag₃PO₄@RGO was synthesized by the method of electrostatically driven self-assembly and photoreduction.Finally,Ag₃PO₄@RGO@La,Cr:SrTiO₃ was synthesized by modification of La,Cr:SrTiO₃.The introduction of RGO not only improves the specific surface area of the system but also enhances the absorption intensity of visible light.When the RGO content in Ag₃PO₄@RGO is 2 wt%,the reaction rate constant（k）for photocatalytic degradation of Rh B is 0.5 min^-1,which is 3.33 times that of Ag₃PO₄.When the mass ratio of La,Cr:SrTiO₃and Ag₃PO₄@RGO in Ag₃PO₄@RGO@La,Cr:SrTiO₃ is 1:10,the k of degradation of Rh B by Ag₃PO₄@RGO@La,Cr:SrTiO₃ is 0.79 min^-1,which is 1.58times that of Ag₃PO₄@RGO and 5.27 times that of Ag₃PO₄,respectively.Ion interference experiments show that K⁺,Na⁺,NO₃^-and SO₄^2-will not affect the catalytic activity of Ag₃PO₄@RGO@La,Cr:SrTiO₃ on the degradation of Rh B,and the presence of Cr⁶⁺and Cl^-will greatly weaken its catalytic performance.The results of free radical sacrifice experiments and electron paramagnetic resonance（EPR）experiments show that the main active substances of Ag₃PO₄@RGO@La,Cr:SrTiO₃ toward the degradation of Rh B are superoxide radicals（·O₂^-）and h⁺,while for 2,4-DNP is hydroxyl radical（·OH）.The above experimental results also prove that the electron transfer mechanism in the system of Ag₃PO₄@RGO@La,Cr:SrTiO₃ belong to Z-scheme mechanism.Cyclic degradation experiments show that the stability of the as-prepared catalyst from high to low in the order of:Ag₃PO₄@RGO@La,Cr:SrTiO₃>Ag₃PO₄@RGO>Ag₃PO₄.（2）Preparation of Ag₃PO₄/Ti₃C₂ composite photocatalyst and performance and mechanism of photocatalytic degradation of organic pollutants.The single layer of Ti₃C₂ was obtained by the etching method and intercalation-exfoliation method.Then,Ag₃PO₄/Ti₃C₂ was synthesized by an electrostatically driven self-assembly method.Compared with traditional Ag₃PO₄/RGO,Ag₃PO₄/Ti₃C₂ has better carrier separation efficiency and photocatalytic performance.When the content of Ti₃C₂ in Ag₃PO₄/Ti₃C₂is 2 wt%,Ag₃PO₄/Ti₃C₂ has the best degradation effect on methyl orange（MO）.Under visible light irradiation,the k of the degradation of chloramphenicol（CPL）by Ag₃PO₄/Ti₃C₂ is 0.025 min^-1,which is higher than that of Ag₃PO₄/RGO(0.012 min^-1)and Ag₃PO₄(0.007 min^-1).The interference experiment results show that K⁺,Na⁺,Cr⁶⁺,H₂PO₃^-and SO₄^2-will not affect the catalytic activity of Ag₃PO₄/Ti₃C₂.However,the presence of humic acid（HA）and fulvic acid（FA）will greatly weaken the catalytic performance of Ag₃PO₄/Ti₃C₂.The results of free radical sacrificial experiments and EPR experiments show that the main active substance of degradation of selected antibiotics by Ag₃PO₄/Ti₃C₂ is h⁺,and·OH only plays a weak role.The characterization result of X-ray photoelectron spectroscopy（XPS）combined with band theory analysis show that a Schottky junction may be formed at the Ag₃PO₄-Ti₃C₂ interface,which greatly improves the efficiency of carrier separation.Cyclic degradation experiments,X-ray diffraction（XRD）,and transmission electron microscopy（TEM）results show that the stability of the as-synthesized catalyst is in the order of:Ag₃PO₄/Ti₃C₂>Ag₃PO₄/RGO>Ag₃PO₄.（3）Preparation of C-Ag₃PO₄@Ag@Ag I composite photocatalyst and its performance and mechanism for photocatalytic degradation of organic pollutants.Using silver-amino complex as Ag⁺source,Ag₃PO₄ with（100）crystal plane exposed（C-Ag₃PO₄）was synthesized by co-precipitation method,and then C-Ag₃PO₄@Ag@Ag I was synthesized by the method of chemical reduction and ion exchange.Ag has the plasmon resonance effect（SPR）,which enhances the visible light absorption of system and also acts as an electronic medium.Under natural light irradiation,C-Ag₃PO₄@Ag@Ag I shows obvious photocatalytic activity for Rh B degradation at various time periods at room temperature.Especially from 10:00 to 14:00,due to the strong solar radiation（average optical power is about 117.5 m W）,it shows the best performance and can completely remove Rh B within 1 h.Interestingly,C-Ag₃PO₄@Ag@Ag I maintains a decent catalytic activity even under very weak light conditions（0.2～6.7 m W,16:00-19:00）.C-Ag₃PO₄@Ag@Ag I show good catalytic activity to Rh B and bisphenol A（BPA）in sunny days（average optical power was 120m W）,and its removal efficiency of Rh B and BPA could reach 100%and 85%within80 min,respectively,which are significantly better than C-Ag₃PO₄.The results of free radical sacrificial experiments and EPR experiments show that the main active substances in the degradation process of C-Ag₃PO₄@Ag@Ag I are h⁺and·O₂^-,and the electron transfer mechanism of the system is follows Z-scheme mechanism.Cyclic degradation experiments and scanning electron microscope（SEM）results showed that the modification of Ag@Ag I enhanced the stability of C-Ag₃PO₄.（4）Preparation of Ag₃PO₄/perylene diimide derivative supramolecular（PDIsm）composite photocatalyst and its performance and mechanism for photocatalytic degradation of organic pollutants.Ag₃PO₄/PDIsm was synthesized by the method of self-assembly and precipitation.The introduction of PDIsm not only enhances the absorption of visible light but also improves the reducing ability of the system.When the content of PDI in Ag₃PO₄/PDIsm is 2 wt%,Ag₃PO₄/PDIsm has the best degradation effect on Rh B.Under visible light irradiation,the removal rate of TC-H by Ag₃PO₄/PDIsm was 82.2%within 8 min,which was much higher than that of PDIsm（20%）and Ag₃PO₄（66.7%）.The results of free radical sacrifice experiments and EPR experiments show that the main active materials in the degradation process of Ag₃PO₄/PDIsm are h⁺and·O₂^-.Above experimental result combined with the results of XPS,it can be speculated that the electron transfer mechanism of the system is follows Z-scheme mechanism.Cyclic degradation results showed that the modification of PDIsm enhanced the stability of Ag₃PO₄.