【作者】 吴伟；

【导师】 赵雅萍；

【作者基本信息】 华东师范大学 ， 环境科学， 2010， 硕士

【摘要】 天然水体中的腐殖质约占水中总有机物50%以上。腐殖酸在水体中可以产生令人不愉快的色和味,同时在氯消毒过程中产生多种消毒副产物,因此腐殖酸被确定为氯消毒过程中形成卤化物的主要前驱物质,成为饮用水微污染严格控制的对象。光催化技术是近20多年来研究较为广泛的水处理方法。自从1976年Carey提出了多氯联苯可以在UV/TiO2作用下分解以来,很多人对水中的有机污染物进行了大量光催化氧化分解研究,本文正是基于这样的研究背景探讨了二氧化钛光催化体系对水体腐殖酸的去除作用,主要研究内容包括：腐殖酸降解和矿化的影响因素分析、降解过程分析、降解机理分析、模拟消毒过程并评价体系去除消毒副产物生成势的效果。首先,进行经济、高效催化剂的筛选。通过各种晶形二氧化钛和银离子修饰的二氧化钛催化剂对腐殖酸降解性能的比较,得出市售P25具有良好的催化性能且简单易得,而用金属银修饰的二氧化钛虽然在降解性能上略优,但是制备过程相对复杂,不经济。探讨了各种反应条件,如催化剂质量浓度、光照强度、溶液pH值、溶液初始浓度、通气量等对光催化体系的影响。结果表明,对于质量浓度为20mg/L,初始TOC浓度为7mg/L的腐殖酸,提高催化剂的质量浓度、光照强度均能在一定程度上促进腐殖酸的降解和矿化；初始浓度低的条件比高浓度条件下的降解速度快；溶液的酸度越高,降解效果越好,在高碱度的条件下不利于腐殖酸的降解,这主要是由于酸性条件下更有利于腐殖酸在二氧化钛表面的吸附和传质；向溶液通入空气的实验中,体系并没有表现出比未通入空气条件下更好的效果,这可能是由于氮气对溶液中传质的阻碍抵消了氧气在抑制光生电子和空穴上的积极作用；向溶液中加入过氧化氢也不能明显提高降解和矿化效率,这可能是因为过氧化氢一方面能够增大溶液中羟基自由基的产生量,另一方面过氧化氢作为羟基自由基清除剂也能够清除溶液中的自由基；银离子修饰催化剂在反应初期有更强的降解效率,这也为工业上的利用提供了一个很好的思路。吸附实验表明,银离子的载入加强了催化剂对腐殖酸的吸附能力；光催化剂在重复利用十次之后还能保持80%以上的降解和矿化效率。各条件下的降解反应均能较好的满足L-H一级反应动力学方程。其次,本文利用尺寸排阻色谱(SEC)和液相色谱有机碳检测仪(LC-OCD)研究腐殖酸在降解过程中分子结构的变化,分析结果表明有疏水性物质(HOC)、可色谱分析的溶解性有机物(CDOC), CDOC则由腐殖质(Humics)、中性物质(Neutrals)、有机酸(Acids)以及其它组成成分(Building Blocks)构成。腐殖酸的降解遵循由大分子逐渐降解成为小分子的模式,具体表现为低浓度疏水性物质(HOC)被降解,其它组分物质经过降解浓度逐渐降低且最终被完全矿化为小分子酸性物质、CO2、H2O。当用负载银的催化剂时,降解过程类似但降解的中间产物有所不同且降解反应发生的更快。再次,利用荧光分析法验证了光催化反应的自由基机理并且阐述了固液界面催化化学应的进行机制,更好地验证了光催化是一个集吸附、富集、光催化、脱附、再生等五个步骤的过程,其中吸附是光催化进行的前提条件。最后,实验室模拟了饮用水的消毒过程,在光催化的作用下,水体的消毒副产物生成势几乎能完全去除,氯仿生成量从未降解前的326μg/L降到10μg/L左右,降解效率达到95%以上,可见二氧化钛光催化在饮用水消毒方面的良好前景。更多还原

【Abstract】 The HA (Humic Acid) accounts for more than 50% of the total organics in the natural water body, which can produce undesirable color and smell. During the disinfection process in the drinking water treatment, it can produce disinfection byproducts as a precursor agent which is harmful to the water itself, now HA has become the object under strict control in the drinking water supply industry. Photo-catalytic oxidation process has grown to be a widely-used water treatment technology in the past 20 years and many researchers worldwide has performed deep studies on it since Carey succeeded in degrading the PCBs under UV/TiO2 system. On this basis, this paper studied the photocatalytic degradation of HA and the whole study can be divided into the four parts as follows:effect factors on the degradation and mineralization of HA, degradation process analysis, mechanism analysis, removal efficiency of THMFPs.The catalysts selection was operated firstly in order to select out the catalysts both economical and easy to get, by comparing the degradation efficiency of different catalysts with different crystals in the form of pure catalyst and Ag-doped counterparts, the result showed that the pure P25 has good efficiency though it is a bit lower than the Ag-doped P25, but it surely can be available more easily. Under the formal condition with the initial HA mass concentration being 20mg/L and TOC being 7mg/L, the factors effect was studied which told us that with the increase of catalyst dosage and UV strength, the efficiency was also increasing to some extent, while pumping air was not helpful, this could be explained as the Nitrogen might disturb the adsorption process of HA onto TiO2 surface though the added oxygen could prevent the recombination of electron and cavity. Similarly, the addition of H2O2 into the system did not make evident improvement on degradation and mineralization either, for one something, the H2O2 improves the production of·OH meanwhile it also assimilates the generated·OH as a clearance agent. In the acid ambient, the HA was degraded faster than in the alkaline environment which should be attributed to the enhanced adsorption ability. As for the Ag-P25, it got a significant increase in the beginning of the reaction due to the enhancement of the adsorption as the adsorption experiment proved, which gives a good idea to the industry field because the industry can’t bear that long time for the total mineralization of the wastewater. All the reaction kinetics fitted the Langmuir and Freundich equation first-order well and the lower the concentration was the higher the rate parameter was. Besides, the same batch P25 was regenerated for 10 times and the result said the mineralization rate still got up to 80% which demonstrated that the P25 could be recycled quite well for a long time.Secondly, the degradation process of HA was explained by Size Exclusion Chromatography(SEC) and Liquid Chromatography Organic Caborn Dector(LC-OCD) analysis, the combining results told us that during the reaction, the large HA molecular which is consisted of hydrophobic organic carbon, humics, acids, neutrals and building blocks was decomposed into smaller moleculars, in details, the hydrophobic substrates was broke down and the other parts was degraded gradually into small molecular and finally converted into the environmental friendly CO2, H2O and other organic acids. Concerned with the Ag-doped P25, it shortened the degradation time for one thing and for another thing, the intermediates during the process were different.Third, fluorescence analysis was adopted to explain the mechanism of the·OH oxidation and the photo-catalytic reaction happening on the solid-liquid surface, the result showed that photo-catalytic reaction is a combination of adsorption, conglomeration, degradation, mineralization and desorption with the adsorption being the precondition.Finally, the disinfection process was simutated and the THMFPs analysis was executed before and after the HA solution was treated by UV/P25 system. The result indicated that the CHCl3 decreased from 326μg/L to 15μg/L, which supported that the UV/P25 system has great potential and good prospect in the disinfection field of drinking water.更多还原