Preparation Of Silver Phosphate/Phosphate Composites And Their Photocatalyst Degradation Properties Under Visible Light

Nowadays,semiconductor photocatalytic technology has been widely recognized in the field of water pollution and energy sustainable development.Ag₃PO₄ is one of the most widely reported visible light-driven semiconductor materials in the literature in recent ten years.It has a suitable band gap width and high efficiency of visible light absorption,but can dissolves slightly in water,and occurs serious photocorrosion in the photocatalytic process,meanwhile,Ag is a noble metal with high price,these shortcomings limit its practical application.In order to reduce the use-cost of Ag₃PO₄ and further improve its photocatalytic performance,three composite silver phosphate/phosphate photocatalysts Ag₃PO₄/Al PO₄,Ag₃PO₄/Ag₄P₂O₇ and Ag₃PO₄/Ag PO₃ were synthesized in this paper.The X-ray diffraction?XRD?,field emission scanning electron microscopy?FE-SEM?,X-ray energy spectrum?XPS?and uv-vis DRS were used to characterize the phase,particle morphology,valence state of valence electron and optical properties of the samples.Their photocatalytic activities were evaluated by assessing the degradation of methylene blue?MB?solution,methyl orange?MO?solution and rhodamine B?Rh B?solution on irradiation with visible light.The photocatalytic mechanism was also investigated by adding free radical reagent experiment.The main research contents and results are as follows:?1?Novel non-porous Ag₃PO₄/Al PO₄ composites with a stick shape were synthesized using the homogeneous precipitation method.Under visible light irradiation,the photocatalytic activity of Ag₃PO₄/Al PO₄composites for the degradation of MB and MO solution is higher than that of pure Ag₃PO₄,and is proportional to the molar content of Ag₃PO₄ in Ag₃PO₄/Al PO₄ composites.The degradation kinetic constants are in the photocatalyst?Ag₃?_0.9Al_0.1PO₄ is 2.154 times than that of Ag₃PO₄.The homogeneous co-precipitation of Al PO₄ and Ag₃PO₄ changed the particle morphology of Ag₃PO₄,effectively prevent the combination of electron-hole pairs,improve the photocatalytic degradation efficiency and reduce the production cost of photocatalyst.?2?Ag₃PO₄,Ag₄P₂O₇ and Ag₃PO₄/Ag₄P₂O₇ composites were synthesized by direct precipitation method.The obtained sample particles are irregular morphology with diameter of 0.5?2?m.Under visible light irradiation,the photocatalytic activity of Ag₃PO₄/Ag₄P₂O₇ composites for the degradation of MB and MO solution is higher than that of pure Ag₃PO₄,and is proportional to the molar content of Ag₃PO₄ in Ag₃PO₄/Ag₄P₂O₇composites.The degradation kinetic constants are in the following order:(0.110 min^-1)>k[Ag₄P₂O₇](0.027 min^-1)?The maximal degradation rate of photocatalyst?Ag₃?_0.9Al_0.1PO₄ is 3.264 times than that of Ag₃PO₄,and better than that of?Ag₃PO₄?_0.9?Al PO₄?_0.1(0.287 min^-1)?DRS results show that Ag₃PO₄/Ag₄P₂O₇ composites are nested composites,which can effectively reduce the recombination of electron-hole pair,thus improving photocatalytic degradation efficiency and stability.?3?Ag₃PO₄/Ag PO₃ composites were synthesized by direct precipitation method.The obtained sample particles are irregular morphology with diameter of 0.5?2?m,similar to the Ag₃PO₄/Ag₄P₂O₇composites.Under visible light irradiation,the photocatalytic activity of Ag₃PO₄/Ag PO₃ composites for the degradation of MB solution is also higher than that of pure Ag₃PO₄,and is proportional to the molar content of Ag₃PO₄ in Ag₃PO₄/Ag PO₃ composites.The degradation kinetic constants are in the following order:k[?Ag₃PO₄?₉?Ag PO₃?₃](0.305 min^-1)>photocatalyst?Ag₃?_0.9Al_0.1PO₄ is 2.77 times than that of Ag₃PO₄.?4?Of all prepared three Ag₃PO₄/phosphate composites,the order of Ag₃PO₄/Al PO₄.?5?There are two main reasons why three silver phosphate/phosphate composites can improve photocatalytic degradation efficiency.First,in the photocatalytic degradation process,pure Ag₃PO₄ only has photogenic holes?h⁺?for catalysis,while Ag₃PO₄/phosphate composites has two free radicals of photogenic holes?h⁺?and superoxide free radicals?·O₂^-?for catalysis.Second,photogenerated electrons?e^-?generated from Ag₃PO₄can be transferred to the coexistence of phosphates,which prevents recombination of photogenic holes-electron pair and prolongs the lifetime of holes?h⁺?,thus improving the catalytic oxidation capacity of free radicals to organic compounds.