含铁纳米材料用于四氯化碳还原脱氯的相关机理研究

发布时间：2018-02-28 19:23

本文关键词： 含铁纳米材料希瓦氏生物合成 FeS纳米颗粒四氯化碳还原脱氯　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：近年来,含铁的纳米材料,包括纳米零价铁以及纳米铁矿物材料,在污染物降解、环境修复以及生物化学元素循环等方面发挥着重要作用,因而得到了广泛关注与研究。其中,纳米零价铁是一种成本低、环境友好且具有良好的还原性能的纳米铁材料,可以处理水体中存在的多种污染物。但是在应用过程中,纳米零价铁的活性会随着反应的进行而不断降低,主要是因为在降解过程中不断生成铁氧化物致使纳米零价铁钝化而导致的,这种钝化现象限制了纳米零价铁的应用。另外一方面,生成的铁氧化物又可以进一步被还原为次级铁矿物,微生物体系可以大大加速这个过程,但是相关机理并不明确。本论文旨在解决上述所提到的问题,并主要研究两种含铁纳米材料(纳米零价铁和纳米FeS材料)对氯代有机物(四氯化碳)的还原脱氯过程以及相关机理。四氯化碳是环境中普遍存在的难降解有机物,并且对自然生态系统和人体健康都具有危害作用。1.首先,我们研究了在非缓冲体系中纳米零价铁对四氯化碳的还原脱氯过程。研究表明,在非缓冲体系中,纳米零价铁可以维持较高的还原脱氯活性,并且能够持续多个降解周期。在第二个反应周期,还原脱氯的速率常数有明显的增加,之后脱氯活性维持在一个较高的水平。最后,降解速率又逐渐降低。在整个还原脱氯过程中,体系的pH维持在7.0-7.8的范围内,和之前报道的相关体系有所不同。实验结束后对体系中的材料进行表征,结果显示纳米零价铁反应之后形成的铁氧化物发挥着重要作用,可以使整个体系形成一个自缓冲体系并使pH维持在相对稳定的范围,从而使纳米零价铁能够长时间的维持较高的还原脱氯活性。这部分内容让我们对纳米零价铁的脱氯过程有了更新的认识,并且有望提高纳米零价铁在污染物降解和环境修复过程中的反应活性并能延长反应寿命。2.接下来,本文研究了环境水体中磷酸盐的存在对纳米零价铁脱氯过程的影响。磷酸盐在水体中可以起到pH缓冲和结合二价铁离子的作用,我们分别在缓冲体系和非缓冲体系中来研究纳米零价铁对四氯化碳的还原脱氯过程。在缓冲体系中,纳米零价铁对磷酸盐存在很强的物理吸附并且生成了大量的磷酸亚铁沉淀(兰铁矿,vivianite),同时生成了大量的H2,导致纳米零价铁被很快消耗,并且反应活性大大降低。但是在非缓冲体系中,磷酸盐的存在使体系的pH有所升高,进而纳米零价铁的腐蚀产氢反应减慢,对四氯化碳的脱氯作用没有受到太大影响,所以磷酸盐的存在在一定程度上延长了纳米零价铁的使用寿命并且提高了其还原脱氯活性。3.报道了生物法合成FeS纳米材料并用于四氯化碳的还原脱氯研究。硫化氢是环境中普遍存在的一种污染物,一般会在厌氧体系中生成,并且对微生物具有毒害作用,严重影响了微生物降解污染物的活性。同时在环境中存在着很多金属还原微生物,金属还原菌在污染物降解以及地球化学元素循环过程中起着重要的作用,例如最普遍的金属还原菌Shewanella菌。近年来有报道金属还原菌在金属还原过程中可以合成纳米材料,而这种生物合成的纳米材料是否会影响微生物对污染物降解以及其相关机理并不清楚,本文对此进行了深入的研究。Shewanella可以还原三价铁生成二价铁,同时可以还原某些含硫化合物(例如硫代硫酸盐)生成负二价的硫离子,从而可以在Shewanella菌的细胞内以及细胞外生成FeS纳米颗粒。结果表明,这种生物合成的FeS纳米材料可以大大加快微生物对四氯化碳的还原脱氯,其还原脱氯速率是单纯微生物脱氯体系的8倍。并且生物合成的FeS纳米材料的还原活性是化学法合成的FeS纳米材料的5倍。对材料的表征结果表明,相比于化学合成的FeS纳米材料,生物合成的纳米材料具有良好的分散性,其中微生物起到了很好的分散剂的作用。另外,生物法合成的FeS纳米材料含有更多还原性的物质,使生物法合成的FeS纳米材料的还原脱氯活性更高。本研究表明生物合成的纳米材料在污染物降解以及环境修复方面具有很好的应用潜能。
[Abstract]:In recent years, nano materials containing iron, including nano zero valent iron and nano iron mineral materials, the degradation of pollutants, plays an important role in environmental remediation and bio chemical recycling and other aspects, so it has been widely concerned and studied. The nano zero valent iron is a kind of low cost, environmentally friendly materials and nano iron with the reduction of good performance, can handle a variety of pollutants in water. But in the application process, the activity of nano zero valent iron and continuously decreased with increasing reaction time, mainly due to the degradation process of continuous production of iron oxide in nano zero valent iron passivation, passivation of this application is limited nano zero valent iron. On the other hand, iron oxide formation can be further reduced to secondary iron minerals, microbial system can greatly accelerate the process, but the mechanism is not related Clear. This paper aims to solve the above mentioned problems, and mainly studies two kinds of iron containing nanoparticles (nano zero valent iron and nano FeS materials) of chlorinated organic compounds (carbon tetrachloride) reductive dechlorination process and related mechanism. The refractory organic matter carbon tetrachloride is ubiquitous in the environment, and have.1. first harmful effects on natural ecosystems and human health, we studied in non buffer system of zero valent iron on carbon tetrachloride dechlorination process. The results show that in non buffer system, nano zero valent iron can maintain higher dechlorination activity, and can continue a degradation cycle. In second a cycle of reaction, the rate constants of reductive dechlorination were increased after dechlorination activity remained at a high level. Finally, the degradation rate was gradually decreased. The reductive dechlorination process, pH system maintenance In the range of 7.0-7.8, the related system and the previously reported different. After the end of the experiment were used to characterize the system in the material, results indicated that nano zero valent iron reaction of iron oxide formation plays an important role, can make the whole system to form a self buffer system and make pH maintained at a relatively stable range, thus the nano zero valent iron can be maintained for a long time the dechlorination activity is higher. This part makes us dechlorination process of nano zero valent iron has been updated, and is expected to improve the reaction activity of nano zero valent iron in the repair process and degradation of pollutants in the environment and can prolong the life of the reaction of the.2. study on the influence of phosphate in environmental water dechlorination process of nano zero valent iron phosphate. And combined with pH can play a buffer role of two valent iron ions in the water, we are in slow Flushing system and non buffer system to study nano zero valent iron on carbon tetrachloride dechlorination process. In buffer system, nano zero valent iron on phosphate has strong physical adsorption and a large amount of ferrous phosphate precipitation (blue iron ore, Vivianite), while generating a large number of H2, leading to nano zero valent iron was quickly consumed, and the reaction activity is greatly reduced. But in the presence of phosphate in the buffer system so that the system's pH increased, and the nano hydrogen corrosion reaction is slowed down by zero valent iron, didn't have too much influence on the dechlorination of carbon tetrachloride, so the presence of phosphate in a certain extent, extend the nano zero valent iron life and improve the dechlorination activity of.3. synthesized FeS nano materials and biological method for reductive dechlorination of carbon tetrachloride. Hydrogen sulfide is a kind of pollution widely exist in the environment The dye, usually produced in the anaerobic system, and has toxic effects on microorganisms, seriously affecting the microbial degradation of pollutants in the environment and activity. There are a lot of metal reducing microorganisms, metal reducing bacteria play an important role in the degradation of pollutants and geochemical cycle, for example, the most common metal reducing bacteria Shewanella bacteria. In recent years can synthesis of nano materials in metal reduction process reported metal reducing bacteria, and the biosynthesis of nano materials will affect the microbial degradation of pollutants and the shutdown of science is not clear, this paper makes a in-depth study of.Shewanella can generate two reduction of ferric iron, and can restore some sulfur compounds (such as thiosulfate) generated negative sulfur ion valence two, thus the Shewanella bacteria cells and exogenous cells FeS nanoparticles. The results show that the biosynthesis of FeS nano materials can greatly speed up the microbial reductive dechlorination of carbon tetrachloride, the dechlorination rate is 8 times higher than that of pure microbial dechlorination system. Reducing activity of FeS nano materials and biosynthesis is 5 times the FeS nano materials into the chemical process of materials. The results showed that compared to the chemical synthesis of FeS nano materials, nano materials synthesis has good dispersion, the microorganism played a very good dispersant effect. In addition, FeS nano materials synthesized by biological method containing more reductive substances, FeS nano materials synthesis biological reduction method dechlorination activity. This study shows that nano material has good application potential in the biosynthesis and degradation of pollutants in environmental remediation.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X703;TB383.1

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