Study On Preparation Of Titaium-based/Ag₃PO₄ Composite Material And Degradation Of Tetracycline Wastewater

Tetracycline antibiotics are used in large quantities in China,and their wastewater will bring potential risks to the ecological environment.Because they contain naphthol rings and other structures that are difficult to degrade,their removal methods are currently immature.TiO₂ photocatalytic technology has become the most promising treatment technology because of its super redox ability,low price and no secondary pollution.However,the wide band gap,high electron-hole recombination rate and small specific surface area of TiO₂ limit its practical application.TiOF₂ is a visible light catalyst newly discovered in recent years,but it also has practical problems such as low degradation efficiency and instability.Ag₃PO₄ has good visible light response,but it has the problem of being easily corroded by light.This thesis aims to prepare a titanium-based/Ag₃PO₄ composite photocatalyst with good solar photocatalytic performance.First,butyl titanate and hydrofluoric acid were used as precursors and glacial acetic acid as solvent to prepare TiOF₂ crystals by hydrothermal method at 180?,and then Ag₃PO₄/TiOF₂ and Ag₃PO₄/TiO₂/TiOF₂ were prepared by using different hydrothermal temperatures.Finally,TiOF₂ was treated with NaOH and then composited with Ag₃PO₄ to obtain OH-Ag₃PO₄/TiO₂/TiOF₂ composite photocatalyst.Tetracycline hydrochloride wastewater was used as simulated target pollutant to analyze the photocatalytic performance of the samples,XRD,SEM,BET,FT-IR,UV-Vis DRs and PL were used and the degradation mechanism.The result is as follows:(1)When the hydrothermal temperature is 90? and disodium hydrogen phosphate provides phosphate,the Ag₃PO₄/TiOF₂ binary composite catalyst is prepared;When the hydrothermal temperature is 180? and sodium phosphate provides phosphate,TiOF₂ can be converted to TiO₂ to prepare Ag₃PO₄/TiO₂/TiOF₂ ternary composite catalyst;In order to improve the catalytic effect,TiOF₂ was treated with NaOH and then hydrothermally composited at 180? to obtain an OH-Ag₃PO₄/TiO₂/TiOF₂ ternary composite catalyst.In the binary composite catalyst TiOF₂:Ag₃PO₄-1:10,the Ag₃PO₄ grains become smaller and the catalysts has a larger specific surface area(46.58 m²/g)than TiOF₂,which is conducive to generating more active sites on the catalyst surface;Its forbidden band width is 2.25eV,which is significantly lower than pure TiOF₂(3.29eV),which improves the utilization rate of sunlight;At the same time,it's electron-hole recombination rate decreases,and the lifetime of photogenerated carriers increases.The degradation rate of the TiOF₂:Ag₃PO₄-1:10 composite sample with a dosage of 200 mg/L for 10 mg/L tetracycline hydrochloride is 66.45%,which is higher than that of pure Ag₃PO₄(63.63%)and pure TiOF₂(12.41%)samples and repeats after 5 times of usage,the degradation efficiency is still 62.85%.This is due to the electron transfer between Ag₃PO₄ and TiOF₂,which makes the silver phosphate photogenerated electrons transfer to the TiOF₂ nanoparticles at the interface,reducing the photocorrosion effect of silver phosphate.The capture experiment proves that·O₂^-plays a leading role in the catalyst reaction process.(2)With the formation of TiO₂,the ternary composite catalyst TiO₂/TiOF₂:Ag₃PO₄-1:10 has a larger specific surface area(53.48 m²/g),which is beneficial to provide more active sites;Its band gap is 1.80eV,which is lower than Ag₃PO₄(2.09eV),which improves the utilization rate of sunlight;at the same time,the electron-hole recombination rate reduces and the lifetime of photogenerated carriers increases.The degradation rate of the composite sample with a dosage of 200 mg/L for 10 mg/L tetracycline hydrochloride is 94.14%,which is much higher than that of TiOF₂:Ag₃PO₄-1:10 composite sample.After repeated use for 5 times The degradation efficiency is still 81.05%.This is due to the electron transfer between Ag₃PO₄ and TiO₂ and TiOF₂,which makes the silver phosphate photogenerated electrons easily transferred to the TiO₂ and TiOF₂ nanoparticles at the interface,reducing the photocorrosion effect of silver phosphate.The capture experiment proves that·O₂^-and·OH play a leading role in the reaction process.In order to improve the catalytic perfformance,TiOF₂ was first treated with NaOH to obtain OH-TiOF₂ and then compounded with Ag₃PO₄ to obtain OH-Ag₃PO₄/TiO₂/TiOF₂ composite catalyst.In the composite sample Ag₃PO₄ exhibits a tetrahedral morphology that exposes {222}high-energy crystal planes,which improves the photocatalytic efficiency;its surface is rough and the crystal grains are smaller,and thus has a larger specific surface area(74.25 m²/g),which can provide more active sites;at the same time,it has a lower electron-hole recombination rate than TiO₂/TiOF₂:Ag₃PO₄-10:1.It's lifetime of photogenerated carriers increases.The degradation rate of 200 mg/L dosage of OH-TiO₂/TiOF₂:Ag₃PO₄-10:1 for 10mg/L tetracycline hydrochloride is 87.70%,which is 31.83%higher than that of TiO₂/TiOF₂:Ag₃PO₄-10:1.After repeated use for 5 times the degradation efficiency is still 84.71%.The capture experiment proved that·O₂^-played a leading role in the experiment.