【作者】 侯利玮；

【导师】 张晖； Sebastien Royer；

【作者基本信息】 武汉大学 ， 环境工程， 2013， 博士

【摘要】 基于羟基自由基反应的高级氧化技术(AOPs)已被广泛的应用于生物难降解有机污染物的去除中。随着高级氧化技术的不断发展,其定义有了新的内涵。除了羟基自由基,其他活性极强的自由基,如硫酸根自由基也可以与难降解的有机污染物之间发生电子转移等反应,使水体中有毒的大分子难降解有机物氧化降解为无毒的小分子物质,从而实现有机污染物的有效去除。目前,最常用的氧化剂有双氧水、臭氧及过硫酸盐类物质。这些氧化剂可以被均相催化剂或非均相催化剂活化而产生自由基类活性物质。然而,均相催化体系有诸多缺点,所产生铁泥对环境会造成二次污染,限制均相催化体系在实际废水处理中的应用。为了解决这些问题,非均相催化体系得到了极大的关注。铁氧化物及一些过渡金属氧化物被用来替代均相催化剂,极大的简化了废水处理的后续分离过程,在氧化降解过程结束后被回收利用,避免了对环境的二次污染。不同种类的氧化剂在催化剂表面得以活化,所产生的羟基自由基及其他活性自由基物质可以有效的分解难生化类有机污染物,而且矿化效果较好。铁及过渡金属氧化物在自然环境中的含量丰富。特别是铁氧化物,常用于催化体系中。本论文选用了三种具有不同组分、结构、比表面积、粒径及活性位浓度的金属氧化物(四氧化三铁、镧钴及镧锰复合态氧化物)作为非均相催化剂,以双氧水、过硫酸盐及臭氧为活化剂,构筑高效催化氧化体系用于有机物污染的废水的氧化降解。在我们的工作中,我们通过对两种有机污染物的催化降解的研究,着重考察了非均相催化氧化体系中的催化机理、有机污染物的生物毒性的变化及矿化度的变化趋势。此外,通过采用与其他高级氧化技术耦合的技术,提高了催化剂的稳定性和其催化活性。本论文主要的工作包括以下几部分：(1)采用超声强化四氧化三铁活化双氧水,对此过程中产生的羟基自由基降解四环素类抗生素-四环素(TC)进行了研究。在该非均相Fenton体系中,研究了不同影响因素对四环素降解的影响、催化反应过程中生物毒性变化及催化反应机制。这些研究结果表明,催化剂的稳定性在超声存在的条件下得到了极大的提高。在该催化体系中,一种新型的膜分离体系被成功的应用于研究表面催化氧化机制,并得出表面羟基自由基是该催化体系的主要活性物质。(2)过二硫酸盐被作为另外一种氧化剂,也可以被四氧化三铁、超声所活化,从而产生硫酸根自由基和羟基自由基两种活性物质,实现对四环素的有效催化降解。在超声强化四氧化三铁活化过二硫酸盐的催化体系中,考察了不同的影响因素,如过二硫酸盐浓度、四氧化三铁投加量、超声功率、初始四环素浓度及溶液初始pH值对四环素的降解率的影响。通过采用乙醇、叔丁醇及1,4-对苯醌为自由基捕获剂,对该反应体系下硫酸根自由基、羟基自由基及超氧自由基的作用进行了评估。研究结果表明,在反应中起主要作用的活性自由基为硫酸根自由基和羟基自由基。(3)臭氧作为一种强氧化剂也可以被四氧化三铁所活化。在超声强化四氧化三铁催化臭氧化体系中对四环素的降解进行了研究。对催化氧化体系中影响四环素降解的因素、生化性及生物毒性的变化进行了全面评估。研究结果表明,四环素的降解速率受溶液的pH值、超声功率的影响而发生变化。但在0.3至1.0克/升的催化剂投加量范围内,四环素的降解速率没有收到明显影响。此外,四环素的降解速率会随着自由基捕获剂叔丁醇、异丙醇及氟化钠的投加而收到抑制。在最佳反应条件下,四环素在20分钟内达到完全去除,化学需氧量(COD)的去除率可达41.8%。当催化氧化反应时间延长为120分钟时,COD的去除率可高达89.1%,生物需氧量与化学需氧量的比值(BOD5/COD)为0.694。在反应进行60分钟后,出水的生物毒性达到最大值。随着反应的继续进行,出水的生物毒性逐渐得以下降。最后,通过对催化剂在三次循环使用中四环素降解率的变化及反应溶液中溶出铁的测试,对催化剂在该催化氧化体系中的稳定性进行了考察。(4)尝试改善催化剂的表面特性以提高催化剂的催化性能。以离子液体辅助水热合成法制备出了不同形貌的纳米态四氧化三铁颗粒。对催化剂的形貌、微孔结构进行了X-射线衍射能谱、N2-物理吸附测试、透射电镜和程序升温还原测试。所制备的四氧化三铁样品呈微立方体、纳米球及多孔纳米棒状形态。在非均相Fenton体系中对催化剂的活性进行了测定。商用四氧化三铁的活性较为有限,棒状纳米结构的四氧化三铁在对苯酚的催化氧化降解中呈现出了超常的活性,98%的苯酚被降解,矿化度高达74%。在采用多孔棒状结构的四氧化三铁为催化剂的催化剂重复利用的实验得出,催化剂的稳定性良好,在催化氧化降解有机污染物中有着广阔的应用前景。(5)采用一种新型的溶剂热合成法,成功的制备出了镧锰及镧钴钙钛矿系列的高度结晶纳米复合材料。对样品进行了X-射线衍射谱图、透射电镜、N2-物理吸附等常规表征。与传统溶胶凝胶法制得的纳米颗粒相比,由溶剂热法制得的催化剂具有较大的比表面积、较强的氧化还原性能(通过氢气程序升温还原测试所得)及较小的粒径尺寸。此外,运用氧同位素交换技术对其催化活性进行了评估。研究结果表明,催化剂活性提升的主要原因是催化剂的粒径及比表面积的提高。这些提升都一一与其在非均相Fenton体系中对苯酚催化氧化活性相关联。更多还原

【Abstract】 Hydroyxl radical based advanced oxidation processes (AOPs) are extensively applied to degrade non-biodegrable organic compounds. In these processes, active radical species are produced with the activation of oxidants in an aqueous solution, leading to destroy organic pollutants efficiently. Up to now, the most commonly used oxidants are hydrogen peroxide, ozone, and persulfate. They can be active by the homogeneous catalysts or the heterogenous catalysts. However, the homogenous catalytic processes have some drawbacks, such as iron sludge was produced during the reactions, causing secondary pollution, and the oxidation conditions were limited in narrow pH range. To address these problems, the heterogeneous catalytic processes were of great concern. Iron oxides, minerals, and transition metal oxides were used instead of homogeneous catalysts, simplying the separation processes, and avoiding the secondary pollutions. In this case, the solid catalysts can be recycled after the oxidation processes, and can be further reused. The activiation of the oxidants can initiate on the catalyst surface, and then generated·OH or other active species, leading to obtain high removal and mineralization of non-biodegradable organic compounds.Iron oxide and transistion metal oxides are rich in natural environment. Especially, the iron oxides were the most used in the catalytic processes. In our studies, three kinds of metal oxides, such as iron oxide, lanthanum cobalt oxides and lanthanum manganese mixed oxides, were chosen as the heterogenous catalysts, which have different components, structures, special surface areas, crystal sizes, and active site densities. Two kinds of model organic compounds, hydrochloride tetracycline and phenol, were selected. They are widely used, non-biodegradable, and toxic to the environment. In this work, we focused on the mechanism of the heterogeneous catalytic processes based on degraded two kinds of model pollutants. Batch of experiment showed the heterogeneous catalytic processes are considered as a surface reaction over the metal oxides. In addition, combined with other advanced processes (such as ultrasound, UV) can enhance the catalyst stability and its catalytic activity. The main work of this thesis can separate into followed parts.(1) hydrogen peroxide was selected as an oxidant, and it can be active by the magnetite (Fe3O4). Hydrochloride tetracycline was selected as the model organic compound, and its degradation efficiency over this catalyst was investigated using a coupled ultrasound/heterogeneous Fenton process. The effects of the reaction parameters, the evolution of the toxicity of the system, and the reaction mechanism were addressed. The results demonstrated that the stability of the catalyst was significantly improved when ultrasound was employed during the reaction. More intrestingly, a novel membrane separation system was used to explore the surface oxidation mechanism. It should be noted that the surface hydroxyl radicals were determined to be the major reactive species during this oxidation process.(2) sodium peroxydisulfate (Na2S2O8) can be acted as another oxidant, and it also be activated by magnetite (Fe3O4) and ultrasound to produce sulfate radicals and hydroxyl radicals on the degradation of tetracycline effectively. The effects of Na2S2O8concentration, Fe3O4addition, ultrasonic power, initial concentration and initial pH on the degradation of tetracycline were investigated in the process of Na2S208/Fe3O4/ultrasound. The results showed that the removal efficiency of tetracycline increased with the increase of Fe3O4dosage, but decreased with the increase of initial pH and initial tetracycline concentration. The quenching effect was examined by using ethanol, tert-butyl alcohol and1,4-benzoquinone under ultrasound irradiation to evaluate the roles of sulfate radicals, hydroxyl radicals and superoxide radicals. The results indicated that sulfate radicals and the hydroxyl radicals played the major roles for the degradation.(3) ozone was employed as the oxidant, and it also can be activated by magnetite catalyst. The degradation of tetracycline was investigated using the ultrasound-enhanced magnetite catalytic ozonation process (US/Fe3O4/O3). Thorough assessments of the operational parameters, biodegradability and acute toxicity were performed. The results indicated that the TC degradation rate was strongly influenced by the initial pH and the ultrasonic power density over the range investigated, but it was almost independent of the dosage of Fe3O4at the range of0.3-1.0g L-1. The TC degradation rate was diminished in the presence of tert-butanol, isopropanol and NaF. Under the optimized conditions, TC was almost completely removed after20min of treatment, and the COD removal reached41.8%. The COD removal further increased to89.1%when the reaction time was extended to120minutes, and the corresponding biochemical degradability (BOD5/COD) rose to0.694. The acute toxicity reached its maximum value after60min treatment and then decreased with further reaction time. The catalyst stability was evaluated by measuring the TC removal rate and iron leaching for three successive cycles.(4) to enhance the catalytic performance, we try to optimize the catalyst surface properites. Nanostructured Fe3O4particles with different shapes were obtained via an ionic liquid assisted hydrothermal process. The morphology and microstructure of the nano-sized Fe3O4particles were characterized using X-ray diffraction, N2physisorption, transmission electron microscopy, and temperature-programmed reduction. As-prepared magnetite samples show microcube, nanosphere, and porous nanorod morphologies. Activity of the nanostructures was evaluated for the Fenton reaction, using phenol as model molecule. While commercial Fe3O4presents very limited activity, rod-type nanostructure exhibited exceptional activity toward phenol removal under mild conditions;98%phenol was removed, and the TOC removal efficiency was74%. The reusability of porous nanorods of Fe3O4was also investigated after three successive runs, which demonstrated the promising application of the catalyst in the oxidative degradation of organic pollutants. Interestingly, the material activity is strongly affected by the reduction degree, highlighting the beneficial effect of Fe0/Fe3O4mixed phase formation to achieve higher activity.(5) the successful synthesis of highly crystalline nanocomposites, based on LaAxO3(A=Co, Mn) perovskites, are reported via a novel non-aqueous thermal route. The final materials were characterised by X-ray diffraction, transmission electron microscopy and N2physisorption. The solid obtained by this non-aqueous route presents a large difference in specific surface area, redox properties (as measured by reduction by H2), and lower crystallite size, when compared to conventional methods. The reactivity was evaluated using oxygen isotopic exchange (OIE). The results obtained from the exchange reaction showed that the activity was strongly influenced by the crystal size and surface area. These observations correlated well with catalytic activity for phenol conversion under the heterogenous Fenton processes.更多还原