Study On Preparation Of Nanometer Zerovalent Iron Composite Material Supported By Sepiolite And Activating Persulfate To Degrade Bisphenol A In Water

Due to the hydrophobicity and non-degradability of bisphenol A（BPA）,traditional sewage treatment methods cannot completely degrade it in a short period of time.Therefore,there is an urgent need to develop new methods to achieve high-efficiency degradation of BPA.In recent years,persulfate advanced oxidation technology has been widely used in wastewater treatment;however,the reaction process between persulfate and Fe²⁺is very rapid and difficult to control,and Fe²⁺has strong reducibility,which may participate in other redox reactions and lose activation.The ability to persulfate.Nano zero-valent iron（nZVI）can replace Fe²⁺to activate persulfate,nZVI can produce Fe²⁺ions under aerobic or anaerobic conditions,thereby activating PS to produce sulfate;nZVI can also directly react with PS to form SO₄^-·.In addition,Fe²⁺can be regenerated by the reaction of Fe⁰ and Fe³⁺on the surface of nZVI,which can recycle ferric ions into ferrous ions,thereby promoting the generation of free radicals and the degradation of pollutants.Use nZVI Replacing Fe²⁺to activate persulfate can effectively make up for the deficiency of Fe²⁺,while avoiding the introduction of anions in the iron salt.However,nZVI has shortcomings such as easy oxidation and easy aggregation,resulting in a significant decrease in its reactivity.In order to solve these problems,we use sepiolite loaded with nZVI to enhance its dispersibility.Sepiolite has a high specific surface area and good chemical stability.The large amount of silanol groups on its surface makes the sepiolite can be used as a metal.And metal oxide carrier.In this thesis,with BPA as the target pollutant,the sepiolite loaded nano-zero-valent iron composite material（S-nZVI）was prepared and characterized,and the S-nZVI composite material coupled persulfate system（S-nZVI/PS）The effect of catalytic degradation of BPA,and the influence of different factors in the S-nZVI/PS system on the degradation of BPA,and the mechanism of catalytic degradation of BPA in this system is discussed.The conclusions are as follows:（1）S-nZVI composites were successfully prepared by liquid phase reduction method,and the morphological characteristics and physicochemical properties of the composites were characterized and analyzed by multiple characterization techniques.The SEM-EDS diagram of S-nZVI material shows that nano-zero valent iron（nZVI）is uniformly dispersed and attached to sepiolite surface.XRD spectra showed that nZVI combined with sepiolite effectively.The BET characterization results showed that the addition of sepiolite increased the specific surface area of nZVI and provided more reaction sites.The XPS spectra showed that the surface of nZVI was slightly oxidized,which covered the nZVI and formed the core-shell structure.Oxygen elements mainly exist in the form of-OH and-O^2-,the-OH functional group belongs to sepiolite,and-O^2-represents the compound with oxygen in S-nZVI.（2）By comparing the degradation effects of different systems on BPA,it was found that the degradation effect of S-nZVI/PS system was significantly better than that of nZVI,S-nZVI and nZVI/PS systems,and the optimal mass ratio of S-nZVI composite to nanoscale zero-valent iron was 1:1.The effects of different reaction conditions on the degradation of BPA by S-nZVI/PS system were investigated.The results showed that when the initial concentration of BPA was 20 mg/L,p H was 5,temperature was35℃,and 0.03 g S-nZVI material was added,the BPA removal rate could reach 100%within 10 min.The effect of inorganic anions on the degradation of BPA in S-nZVI/PS system was investigated.The results show that:low concentrations of Cl^-and NO₃^-have almost no effect on the degradation of BPA.200 m M will have a slight inhibitory effect;SO₄^2-and HCO₃^-showed an inhibitory effect on the degradation of BPA,of which HCO₃^-degrades BPA.The inhibitory effect was very obvious.（3）According to the free radical quenching experiment:SO₄^-·was the main free radical in S-nZVI/PS system under acidic condition,SO₄^-·and·OH were similar under neutral condition,and·OH was the main free radical under alkaline condition.The existence of SO₄^-·and·OH in the S-nZVI/PS system was directly proved by electron paramagnetic resonance analysis.The disappearance of SO₄^-·and·OH signals in the DMPO/PS/S-nZVI/BPA system indicated that the degradation of BPA consumes free radicals.（4）Studying the change of Fe ion concentration in the solution and the residual concentration of persulfate in the S-nZVI/PS system shows that at the beginning of the reaction,,S-NZVI was rapidly consumed and nZVI was converted to Fe²⁺,resulting in Fe²⁺was quickly consumed,the Fe³⁺in the solution increased rapidly,while the reaction rate gradually slowed down in the later stage,and the Fe³⁺in the solution was converted to Fe²⁺by Fe⁰,resulting in an increase in Fe²⁺and a decrease in Fe³⁺in the solution.The PS in the solution was almost consumed 10 min before the reaction,which is consistent with the degradation trend of BPA.At 60 min,the degradation rate of TOC is about 60%,indicating that the S-nZVI/PS system has a good degradation effect on BPA and can mineralize BPA to a large extent.（5）According to GC-MS,the intermediate products that may be produced by S-nZVI/PS system for degradation of BPA were detected,and it was inferred that the possible degradation route of BPA is:through the S-nZVI/PS system SO₄^-·and·OH oxidation,BPA degrades into intermediate products such as 1-methylethylbenzene,acetophenone,toluene,etc.These intermediate products are then ring-opened to form nonanal,undecane,2,3,4-trimethylhexane,2,3-dimethylheptane and other chain organic substances,most of which are completely degraded into carbon dioxide and water.