Preparation Of Ag-graphene-TiO₂ Material And Its Photocatalytic Degradation Of Oxytetracycline

Antibiotics are one of the most popular drugs in China,which are widely used in medical treatment,animal husbandry and agriculture.Antibiotics in water environment are difficult to degrade,stable,easy to enrich and other characteristics,and the existing traditional sewage treatment technology can not achieve efficient removal of them,the pollution caused by antibiotics to water environment has become an urgent problem to be solved.Therefore,it is of great significance to develop a new efficient and non-secondary pollution wastewater treatment technology.Under the concept of green environmental protection development,TiO₂photocatalysis materials possessing high treatment efficiency,simple operation,no secondary pollution and other advantages,is widely applied in antibiotic wastewater treatment,but its existence-electron hole of high recombination rate,low quantum efficiency of photocatalytic limitations,a serious impediment to TiO₂photocatalysis materials applied in the treatment of antibiotic wastewater.How to improve the utilization rate of light by modifying TiO₂has become a hot topic.Based on this,in this paper,graphene,Ag and TiO₂as the main raw materials,Ag-graphene-TiO₂composites were prepared by one-step hydrothermal method combined with UV radiation deposition of precious metals.The effects of three factors,including the dosage of graphene,the amount of silver and the calcination temperature,on the physical and chemical properties of the composites and the degradation efficiency of oxytetracycline were investigated.The effects of composite dosage,initial concentration and p H on the degradation efficiency of oxytetracycline were investigated.The morphology,elemental composition and optical properties of Ag-graphene-TiO₂composites were analyzed by means of scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction and UV-vis.NIR.DRS.The degradation intermediates of oxytetracycline were analyzed by high performance liquid chromatography-mass spectrometry(HPLC-MS),the possible photocatalytic degradation pathways were deduced,and the photocatalytic degradation mechanism was explained.The main conclusions are as follows:(1)The degradation of oxytetracycline by Ag-graphene-TiO₂composites showed that the optimal preparation conditions of the composites were m(GO):m(TiO₂)was1:4,the silver content was 4%,and the calcination temperature was 200?.Under these conditions,the degradation rate of oxytetracycline by the composites could reach 91.63%after 360min.The optimal degradation conditions of oxytetracycline were as follows;Ag-graphene-TiO₂composite dosage of 20mg,initial concentration of oxytetracycline of 10mg/L,solution p H=5,humic acid content of 10mg/L.(2)The characterization results of Ag-graphene-TiO₂composites show that the three materials of Ag,graphene and TiO₂can be successfully composite by one-step hydrothermal method combined with UV radiation deposition of precious metals,and the crystal phase of TiO₂in the composite material is mainly anatase phase.In the process of preparing composites,no other impurities are introduced except graphene and Ag.Coupling the excellent properties of graphene and Ag reduces the crystal size of the composites,increases the specific surface area,inhibits the photogenerated electron-hole composite,and strengthens the photocatalytic performance of Ag-graphene-TiO₂composites.(3)The recovery and utilization experiment of Ag-graphene-TiO₂composite material showed that the composite material had good stability,and the degradation rate of oxytetracycline remained above 75%after being reused for five times.(4)By high performance liquid chromatography mass spectrometry instrument for terramycin intermediate analysis and free radicals to capture the experiment,presumably Ag-graphene-TiO₂composites produced mainly by hydroxyl free radical(·OH)and light holes(h⁺)and super oxide free radical(·O₂^-)to oxidative decomposition of terramycin groups such as strong oxidation,terramycin get efficient degradation;Otetracycline is mainly degraded into small molecules such as H₂O and CO₂through H substitution,dehydration,demethylation,methyl oxidation to aldehyde group and other oxidation reactions.