Study On Degradation Of 1,4-dioxane Pollution By Electro-Fenton System Constructed By Fe Based Molecular Sieve

1,4-Dioxane（1,4-DX）is an emerging organic pollutant that is commonly used as a stabilizer for chlorinated solvents in industry,and is also detected in daily necessities such as cosmetics,deodorants and cleaning agents.Residues of 1,4-DX,different concentrations of1,4-DX pollution can often be detected in the water environment.As a potential carcinogen,it seriously threatens human health and the safety of the natural ecological environment.1,4-DX has the characteristics of high water solubility,low volatility,strong migration and refractory degradation,which makes it difficult to effectively remove it from water by conventional water treatment technology.The ability of advanced oxidation technology to generate oxidative free radicals has gradually attracted widespread attention.Among them,heterogeneous electro-Fenton technology has a wide p H application range and does not produce iron sludge precipitation.It is widely used in the field of water treatment.The combination of technologies forms an adsorption-heterogeneous electro-Fenton degradation combined system,which can quickly remove organic pollutants in water.ZSM-5 has acidic sites,strong ion exchange performance,and high hydrothermal stability,and is often used as an adsorbent and catalyst.Therefore,in this study,iron was loaded on ZSM-5,and a combined adsorption-heterogeneous electro-Fenton degradation technology was developed to deal with 1,4-DX pollution.The main conclusions of the experiment are as follows:（1）In this study,Fe-ZSM-5 molecular sieves with both adsorption and catalytic functions were first prepared by impregnation and roasting method,and the properties of ZSM-5molecular sieves before and after being loaded with transition metal iron were characterized by XRD,SEM,FTIR and BET.The results show that metallic iron is uniformly distributed on the surface of ZSM-5 zeolite,and the iron forms supported on the surface of ZSM-5 zeolite include Fe³⁺and Fe²⁺.Compared with before iron loading,the surface morphology and framework structure of the modified molecular sieve did not change greatly,but the surface area and pore diameter decreased slightly,indicating that the metal iron ions were entering the pores,or the micropores were damaged during the preparation process.（2）The adsorption performance of Fe-ZSM-5 molecular sieve for 1,4-DX was studied,and it was found that the adsorption of Fe-ZSM-5 molecular sieve to 1,4-DX could quickly reach equilibrium within 5 min,and the equilibrium was basically maintained after adsorption.Status unchanged.The adsorption fits a pseudo-second-order kinetic model,indicating that the adsorption is achieved by sharing or transferring electron pairs between Fe-ZSM-5 and1,4-DX.The Langmuir and Freundlich adsorption models were used to fit the adsorption data of 1,4-DX on Fe-ZSM-5 molecular sieves.The adsorption behavior on 5 molecular sieves indicated that the adsorption process of Fe-ZSM-5 molecular sieve to 1,4-DX conformed to the characteristics of monolayer adsorption,and the maximum adsorption capacity was 43.15mg/g.（3）The catalytic performance of Fe-ZSM-5 zeolite for catalyzing heterogeneous electro-Fenton degradation of 1,4-DX was studied by changing the p H of the solution,the dosage of zeolite,the current density and the initial concentration.The optimal experimental conditions are finally obtained by orthogonal experiment as follows:the dosage of molecular sieve is 1 g/L,the initial p H of the solution is 3-5,the current density is 20 m A/cm2,the initial concentration of the solution is 10 mg/L,and the electrolysis time is At 3h,the maximum removal rate of 1,4-DX reached 90.3%.Compared with the traditional electro-Fenton technology,the removal rate of 1,4-DX was improved by about 20%,proving that Fe-ZSM-5 molecular sieve can promote the removal of 1,4-DX.In addition,Fe-ZSM-5molecular sieve itself has acidic sites,which can actively adjust the p H of the solution to the acidic range,and will not produce iron sludge precipitation.The effect of water matrix composition on the removal rate of 1,4-DX was studied,and it was found that chloride ions can promote its degradation,and bicarbonate,humic acid and fulvic acid can inhibit the degradation of 1,4-DX,but have little effect on the adsorption process.Fe-ZSM-5 molecular sieve has good stability and reusability,and it still has a high removal rate of 1,4-DX after 5consecutive cycles.（4）The main mechanism of the degradation of 1,4-DX in the heterogeneous electro-Fenton system constructed by Fe-ZSM-5 zeolite was studied by using free radical inhibitor combined with electron paramagnetic technology,and the degradation mechanism was further analyzed in combination with the types of intermediate products.First,isopropanol and 1,4-benzoquinone free radical inhibitors were used to preliminarily explore the types of free radicals in the system.The results found that isopropanol had a more obvious inhibitory effect on the heterogeneous electro-Fenton system,indicating that.OH is 1,4-DX.The main contributor to the degradation,1,4-benzoquinone also had inhibitory effect,and it was also proved that·O₂^-made a certain contribution to the degradation of 1,4-DX.In addition,the two organic solvents have obvious inhibitory effects on the adsorption properties of Fe-ZSM-5 molecular sieves.Electron paramagnetic technology was used to further explore the free radical species.The free radical species was captured by 0.1M DMPO.The existence of.OH was obviously detected,but the·O₂^-was not detected.Combined with the free radical quenching experiment,it was found that it may be caused by·O₂^-are unstable in nature and cannot be captured by DMPO.The main degradation products of 1,4-DX were determined by gas chromatography-mass spectrometry,and small molecules such as ethylene glycol,acetic acid,propionic acid,acetic alcohol and oxalic acid were detected.Combined with the free radical inhibition experiment,two main degradation products were concluded.Path,1,4-DX is finally degraded into inorganic compounds carbon dioxide and water in the heterogeneous electro-Fenton system constructed by Fe-ZSM-5 molecular sieve.