【作者】 万俊杰；

【导师】 万金泉；

【作者基本信息】 华南理工大学 ， 环境工程， 2014， 博士

【摘要】 氯酚类有机物的应用领域非常广泛，其中2,4-二氯苯酚（2,4-DCP）作为一种有机介质在制药、农药、润滑剂、印染、造纸和化工合成工业中被大量的应用。氯酚类物质因其具有诱变性和致癌性，一旦排放到环境中会对人类健康有着巨大的潜在的威胁。由于其生物毒性和难降解性的特点，寻找一种安全有效、环境友好的降解方法是现在研究的主要内容。近年来纳米零价铁（nZVI）技术用于废水处理受到广泛关注，因该技术具有廉价、高效、无二次污染的特点被认为是氯酚类有机物降解最有发展前景的方法之一。但nZVI技术在脱氯过程中由于其具有的高表面能，使nZVI表面容易钝化，导致nZVI的还原脱氯能力降低，使其在应用上受到了限制。为了解决这个问题，对nZVI表面进行改性是一种行之有效的手段。本文采用一步液相还原法制备了SiO2包覆nZVI（SiO2-nZVI），通过探讨制备工艺条件对SiO2-nZVI的还原脱氯和抗氧化能力的影响，优化了制备工艺条件，并对制备成功的SiO2-nZVI进行了表观表征；同时将SiO2-nZVI和nZVI应用于2,4-DCP的降解研究，对降解影响因素、降解过程中溶液的性质、降解过程中nZVI的表观形态变化、以及降解机制进行了系统的对比研究。SiO2-nZVI制备工艺条件研究。采用液相还原法制备出纳米铁微粒，再采用St ber水解法，使正硅酸乙酯水解生成介孔纳米SiO2，包覆在纳米铁的外层，形成一层网状介孔膜，通过控制介孔直径大小来抑制反应体系中的O2迁移到纳米铁表面，抑制nZVI钝化失去活性。通过探讨异丙醇/H2O体积比、NaOH投加量、TEOS的投加量和制备过程中包覆时间对SiO2-nZVI的抗氧化能力和氧化还原能力的影响，来优化制备条件。分别考察了在添加和未添加1mL聚乙二醇(PEG400)的两种情况下制备出的SiO2-nZVI的性能对比研究，结果显示添加PEG400对制备的SiO2-nZVI的抗氧化性和还原脱氯性有增强作用，比未包覆nZVI对2,4-DCP的去除率提高了近40%。根据纳米铁的抗氧化能力和还原效果优化出最佳制备条件为：异丙醇/H2O的最佳制备参数为1:2、NaOH投加量选择为4mL、TEOS的投加量为2mL及水解时间为4h。对SiO2-nZVI进行了表观表征研究。通过SEM和TEM电镜、傅里叶红外光谱(FTIR)、X射线衍射分析(XRD)、热重分析(TG)对SiO2-nZVI的表观特征及结构进行研究。结果显示，SiO2-nZVI呈现出链状的结构，SiO2-nZVI颗粒是球状的，呈核壳型结构，纳米颗粒粒径为80-100nm。FTIR显示出SiO2-nZVI的外层已经完全被纳米SiO2包覆着，同时外层还有大量的羟基，也证明了SiO2包覆层是靠羟基的结合实现的。XRD显示出纳米SiO2包覆层属于非晶态SiO2。TG图告诉我们，纳米SiO2包覆层中吸附着水，同时证明了纳米铁的氧化物有两种，即Fe2O3和Fe3O4。对比考察了nZVI和SiO2-nZVI在降解2,4-DCP的过程中各影响因素对降解效率的影响。探讨了FeSO4·7H2O的投加量、2,4-DCP的初始浓度、pH以及以及共存阳离子Al3+、Mn2+、Cu2+和阴离子Cl–、PO43–、NO3–对2,4-DCP去除率的影响。优化出最佳的降解工艺条件为单位质量纳米铁去除2,4-DCP的量确定了FeSO4·7H2O的投加量为1.5g时为最佳；2,4-DCP的浓度为150mg/L；pH值为2.73时，两种纳米铁对2,4-DCP去除效果最好。对比研究了nZVI和SiO2-nZVI在降解2,4-DCP的过程中溶液性质的变化及纳米铁表观形态的变化。溶液性质变化这部分研究主要考察了两种体系的溶液pH值的变化、Fe2+和Fe3+两种离子浓度变化、Cl-离子浓度变化、反应体系溶液的UV-Vis的变化四部分内容。对比两种纳米铁表观形态变化的研究包括：对比两种降解过程中两种纳米铁颗粒的FTIR谱图变化以及SEM-EDX图变化情况。结果显示SiO2-nZVI的氧化铁是呈现球状细小均有的颗粒物，而未包覆nZVI氧化后呈现的是多面体晶体结构。对比研究了nZVI和SiO2-nZVI降解途径和机制。两种纳米铁颗粒降解2,4-DCP的产物是相同的（4-CP、2-CP和苯酚），说明降解的机制是相同的，但是nZVI和SiO2-nZVI降解2,4-DCP的进行路径是不同的。2,4-DCP是直接通过扩散作用迁移到未包覆nZVI的表面进行还原脱氯的，即2,4-DCP的还原脱氯过程、nZVI产电子和还原性H原子及铁的钝化作用都是在未包覆纳米铁表面进行的。而包覆纳米铁的反应区域包括三个部分，第一个区域是nZVI产电子和还原性[H]原子是在纳米铁表面进行的；第二个是产生的Fe2+和Fe3+离子被吸附在包覆层的内表面；第三个是2,4-DCP的还原脱氯是在包覆层的外层，而纳米铁的氧化成氧化铁的过程在包覆层外层、内层和纳米铁表面都有发生。更多还原

【Abstract】 Chlorinated organic compounds (COCs) have a wide range of uses. For example,2,4-dichlorophenol (2,4-DCP) is an important organic intermediate, and is widely used in themanufacture of pesticides, pharmaceuticals, lubricants, dyestuffs, and in the synthesis of otherchemicals. Chlorophenols(CPs) in water causes serious problems due to their toxicity arehighly mutagenic or carcinogenic and adverse effects on the human. Removing thesecontaminants from water is a sighificant challenge because of ever-increasing pollution andthe shortage of high quality fresh water. Recently, a chemical reduction method usingzero-valent iron (ZVI) has been widely studied for contaminated wastewater treatment.Earlier studies showed that this is a promising approach for chlorophenol removal because itis cheap, highly efficient, and environmentally friendly. However, using nZVI for treatingchlorinated organics has many drawbacks. For example, the high surface energy makesoxidation of nZVI in the atmosphere easy, which means that the rate constant for thedechlorination of chlorophenol is low, and this decreases the nZVI reducing abilities. In thisstudy, SiO2-coated nZVI using a one-step liquid-phase reduction method was synthesized andthe removal efficiency for2,4-DCP and the oxidation resistance of the SiO2-coated ironparticles was investigated. The effects of SiO2-coating preparation conditions on particlesurface texture, size, reduction efficiency, and antioxidation abilities were also investigated.The degradation characteristics of SiO2-coated nZVI and uncoated nZI were compared withthose of uncoated nZVI.The preparation conditions of SiO2-nZVI were investigated. In the present work, a novelmethod for in situ synthesis of SiO2-coated iron nanoparticles was investigated. The maincharacteristic of SiO2coating of nZVI is that improvements in the oxidation resistance,reducing capacity, coating, and stability of nZVI are accomplished in one step. SiO2-coatingtechnology provides an amorphous mesh structure, stops oxygen migration and nZVI surfaceoxidation, and gives improved pollutants degradation abilities. Core–shell SiO2-coated ironnanoparticles were synthesized using a one-step St ber method in the presence and absenceof PEG400. The2,4-dichlorophenol degradation and anti-oxidation abilities of thenanoparticles were investigated. The effects of isopropanol/H2O ratio, NaOH dosage, tetraethyl orthosilicate (TEOS) dosage, and reaction time used in the synthesis wereinvestigated. The results showed that the nanoparticles were stable in the presence of PEG400.A comparison of the removal rates of2,4-dichlorophenol using pure iron nanoparticles andusing SiO2-coated iron nanoparticles showed an improvement of about40%usingSiO2-coated iron nanoparticles, suggesting that SiO2-coated iron nanoparticles improve theantioxidation abilities and reducing capacity of iron nanoparticles; such nanoparticles couldhave wide applications in chlorophenol degradation. The optimum conditions for preparationcondition of SiO2-nZVI: isopropanol/H2O ratio1:2, NaOH dosage4mL, tetraethylorthosilicate (TEOS) dosage2mL, and reaction time4h.The characterizations of SiO2-nZVI were investigated. The SiO2-coated ironnanoparticles were characterized using transmission electron microscopy, scanning electronmicroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. RepresentativeTEM and SEM images of SiO2-coated nZVI are shown. It can be seen that the bare nZVIparticle size was about80-100nm. Moreover, from the TEM images, we can clearly see thenanoparticles coated with a transparent film. The SEM images shows that the SiO2-coatednZVI were spherical and formed linear chains in space, and the surfaces of the coatedparticles were smooth and uniform. FTIR spectra of the nZVI, SiO2-nZVI and SiO2nanoparticles are shown that the presence of O-H stretching and bending vibrations showTEOS hydrolysis to produce SiO2containing hydroxyl groups, and reveal bonding of SiO2and nZVI by hydrogen, the Si-O-Si stretching vibrations reveal that the surfaces were coatedwith SiO2. The XRD patterns of analytically pure SiO2, freshly synthesized nZVI, and freshlysynthesized SiO2-coated nZVI samples indicated that pure Fe was prepared using the presentprocedures. The diffuse and broad peaks show that the SiO2from the hydrolysis process andSiO2nanoparticles are amorphous. TG was employed to examine the oxidation stability ofnZVI and SiO2-coated nZVI. SiO2-coated nZVI shows the weight loss of the first step due towater and solvent volatilize and the two produts of oxidation of nZVI were Fe2O3and Fe3O4was certified contemporary.Comparison of rates of2,4-DCP removal by nZVI and SiO2-coated nZVI duringdegradation process.2,4-DCP reaction conditions and changes in solution ion concentrationswith reaction progress were investigated. The effects of FeSO4·7H2O dosage,2,4-DCP concentration, pH, and co-existing ions(cations Al3+,Mn2+,Cu2+and anions Cl–,PO43–,NO3–) onthe degradation activity were investigated. The results showed that the efficiency ofSiO2-coated nZVI far exceeded that of uncoated nZVI for removal of2,4-DCP from aqueoussolutions. The best removal conditions were obtained when the FeSO4·7H2O dosage of theSiO2-coated nZVI was about3.0g/L, the2,4-DCP concentration was150mg/L, and the pHwas about2.72at25°C in a volume of100mL.Compared with those using uncoated nZVI,2,4-DCP reaction conditions and changes insolution ion concentrations with reaction progress were investigated. Changes in pH, Fe2+andFe3+concentration, and UV-Vis spectra with reaction time were analyzed. Changes in thesurface properties of the uncoated and SiO2-coated nZVI were characterized using scanningelectron microscopy (SEM), energy dispersive X-ray emission spectra (EDX), andFourier-transform infrared spectroscopy (FTIR). The redox reaction progressed on the nZVIsurface for uncoated nZVI and on the SiO2amorphous coating for coated nZVI. Theamorphous SiO2coatings obtained on the nZVI surface distinctly increased their oxidationresistance.Comparison of degradation products with progress of2,4-DCP degradation by nZVI andSiO2-coated nZVI. The reaction mechanism of the uncoated and SiO2-coated nZVI which hadthe same degradation path that the products were4-CP,2-CP and phenol but different masstransfer mode, was discussed. When nZVI was used alone, the nanoparticles easily andrapidly captured aqueous2,4-DCP easily due to their large surface area. The adsorbed2,4-DCP was partly reduced by electrons and Fe2+on the nanoparticles surface to produce2-CP and Fe3+, respectively, and were finally released back into the solution for phenoldegradation. Then, nZVI surface caused oxidation, which passivated the nZVI surface andreduced the internal electron supply of the particles. nZVI is known to easily react with wateror oxygen in its surrounding media, which results in the formation of an oxidation layer thathinders further reaction. For SiO2-coated nZVI, electrons, Fe2+, and Fe3+were absorbed oninner coating, and2,4-DCP and O2were then adsorbed on the outer coating. Because theoxygen was molecular phase, it was more difficult for it to migrate in the amorphousmicropores of the SiO2coating than the other ions, which increased the active time forreaction. At the same time, the layer strongly adsorbed Fe2+and Fe3+and slowed their migration from the inner to the outer surface, delaying the rate of iron oxide formation andnanoparticle passivation.更多还原