【作者】 沈世豪；

【导师】 赵国华；

【作者基本信息】 同济大学 ， 物理化学， 2008， 硕士

【摘要】 水体中难生化降解的有机污染物呈现出种类多、浓度高、毒性强、结构复杂的特点,因此高级氧化技术(AOP)受到广泛的关注和重视。但采用单一技术往往难以达到理想的降解效果,因此多种高级氧化技术的联用是研究的必然趋势之一。超声强化电化学氧化是一种非常有前途的联用技术。众多研究表明超声可以加快电化学氧化的反应速率,但是目前仍存在以下两个问题。第一,电化学氧化的核心是电极,目前已有的许多电极材料并不能适用于超声强化电化学氧化技术或者不能体现出超声强化的作用。金刚石膜(BDD)电极是近几年内国际上研制出的一种具有电势窗口宽、析氧电位高、背景电流低、化学性能稳定等优点的电极,电化学氧化处理污染物降解的能力强,是未来水处理的理想电极材料。但金刚石膜电极能否在超声的极端情况下稳定、高效地工作,尚需要进一步的论证。第二,由于污染物在电极上发生电化学氧化降解本身就是一个复杂的过程,而超声强化电化学氧化的实质目前研究较少,尤其缺少定量分析的机制研究。本论文从上述两个角度对超声强化电化学氧化降解有机污染物进行了研究,为这一联用技术的实际应用提供了理论基础。论文研究工作取得了以下成果:(1)系统、全面地从电化学氧化的传质过程、吸附与脱附、电极反应三个步骤,研究了超声强化BDD电极电化学降解苯酚和邻苯二甲酸。超声可以增强传质过程,这种强化作用仅取决于超声的强度。污染物在BDD电极表面的电化学吸附特性决定了超声对吸附与脱附过程的作用。超声促进了苯酚的中间产物的脱附,有利于直接氧化;对于邻苯二甲酸,超声使得吸附量进一步减小,导致直接氧化消失。超声可以显著提高BDD电极的降解效率,而且对苯酚降解的促进作用更为明显,这主要是因为超声可以同时强化苯酚的直接氧化和间接氧化,但对于邻苯二甲酸,间接氧化得到了强化,但直接氧化消失。(2)在详细地比较了超声对BDD电极和Pt电极降解苯酚的协同强化效果的实验基础上,证实BDD电极是一种非常适宜于超声电化学协同降解处理工艺的性能优异的电极。超声对BDD电极降解苯酚的强化作用更为明显,并从理论上解释了超声造成BDD和Pt电极强化效果差异的原因。苯酚在两种电极表面的电化学氧化均受扩散过程控制,超声使得BDD电极的扩散系数增大了375%,远大于Pt电极的42%;苯酚在两种电极表面都有很强的吸附,而超声对BDD电极的更新和活化作用更强;同时超声更有利强化污染物在BDD电极表面的电化学反应速率。采用BDD电极降解产生的中间产物种类少于Pt电极;超声的强化作用不会使得中间产物的种类发生改变,但会加快产物产生和进一步氧化降解的速率,缩短达到最高浓度的时间,而这一促进效果在BDD电极上更为明显。(3)比较了苯在金刚石膜电极上的电化学氧化和超声电化学氧化的机理。超声能够促进反应过程中中间产物的脱附,有利于电极表面反应的进行。对于氧化电位高达2.8 V的苯,超声可以极大地促进电化学氧化速率,完全矿化所需时间缩短了49.1%。在电化学氧化过程中,苯首先氧化生成苯酚、对苯二酚、间苯二酚、邻苯二酚和苯醌这些苯环类中间产物,然后进一步氧化生成顺丁烯二酸和草酸,最终实现完全矿化。而在超声强化电化学过程中,超声能够促进中间产物的生成和降解过程。更多还原

【Abstract】 Advanced Oxidation Processes （AOPs） are of great interest because of the increasing variety and amount of non-biodegradable pollutants with complex structures and high toxicity, but it is difficult for a single oxidation process to meet the requirement for wastewater treatment in some cases. Hence, the combination of several oxidation processes has been becoming one of the active research fields in recent years.Ultrasound-enhanced electrochemical oxidation is a promising treatment technology. It has been demonstrated that ultrasound can improve electrochemical oxidation rate effectively, but there still exist two problems. First, the key of electrochemical oxidation is electrode. Many electrodes are not suitable for ultrasound-enhanced electrochemical oxidation, or show the enhanced effect of ultrasound. Boron-doped diamond （BDD） electrode has received wide attention in recent investigations for its excellent properties, such as wide electrochemical potential window, high oxygen evolution potential, low background current and high anodic stability, which is a suitable material for water treatment in the future. But whether BDD electrode can work steadily and efficiently with ultrasound has not been proved. Second, degradation on electrode is a complex process. The influences of US on electrochemical oxidation have not been understood clearly up to now, especially lacking of quantitative analysis.In this paper, ultrasound-enhanced electrochemical oxidation is studied from the two points above, which is of great significance on the applications of this combinative process in environmental engineering. Several study results have been gained:（1） The mechanism of ultrasound-enhanced electrochemical oxidation process for phenol （Ph） and phthalic acid （PA） is investigated from the three steps of electrochemical （EC） oxidation including mass transport process, adsorption and desorption, and electrochemical reaction roundly. Ultrasound （US） has remarkable influences on all steps, which cause the enhancement of degradation for both pollutants. Mass transport process can be greatly accelerated by US. The adsorption amount of Ph decreases with desorption of polymer intermediates promoted by US, which do benefits to direct oxidation. For PA, the adsorption amount decreases by US, with no direct oxidation happens. US can efficiently reduce the average electrochemical oxidation energy consumption, and the enhancement on degradation of Ph is more effective, because mass transport process does not affect degradation efficiency, but the difference in electrochemical properties leads to different oxidation pathway.（2） The enhancement of electrochemical oxidation of Ph on BDD and Pt electrodes assisted by US are compared in detail, and BDD electrode is demonstrated a suitable electrode for ultrasound-enhanced electrochemistry oxidation technology with excellent performance. the difference is explained from mass transport, adsorption and desorption, and electrochemical reaction. The enhanced effect on BDD electrode by US is much greater than that on Pt electrode, and the reason for the difference between BDD and Pt electrodes is explained. Diffusion process is found the controlling step of Ph degradation on both electrodes, and US enlarges the diffusion coefficient on BDD electrode by 375%, much higher than 42% on Pt electrode. Without US, both electrodes are inactivated with large adsorption amount of Ph. With US, the surface of BDD electrode is renewed and activated more effectively. The improvement on electrochemical reaction of BDD electrode by US is much more significant. The variety of intermediates produced on BDD electrode is found less than that on Pt electrode. US can increase production and degradation rates of intermediates, and reduce the time to reach the highest concentration and promote their degradation, without changing the variety of intermediates.（3） The mechanism of degradation of benzene on BDD electrode by electrochemical oxidation and ultrasound-enhanced electrochemical oxidation is compared. US can accelerate desorption of intermediates and promote oxidation on electrode surface. US can improve oxidation efficiency of benzene with the high oxidation potential of 2.8 V largely, and the time needed for total degradation is decreased by 49.1%. In electrochemical process, benzene is oxidated into aromatic compounds such as Ph, hydroquinone, resorcin, pyrocatechin and benzoquinone, then comes to maleic acid and oxalic acid, and is mineralized into CO₂ and H₂O finally. In ultrasound-enhanced electrochemical process, ultrasound can promote producing and degradation of these intermediates.更多还原