【作者】 周蕾；

【导师】 周明华；

【作者基本信息】 南开大学 ， 环境工程， 2013， 博士

【摘要】 电芬顿技术(EF)作为一种新型、高效、清洁的电化学高级氧化技术,近年来备受研究者的关注。由于阴极材料的性能决定了H202的原位生成,从而直接影响电芬顿处理有机污染物的能效,因此探索综合性能好的阴极材料成为该领域的一大研究热点。本研究以三维结构的商品化石墨毡为基础阴极材料,采用化学或电化学方法对材料进行改性,试图改善阴极氧还原反应(ORR)催化活性,在材料表征的基础上,系统的考察了改性过程对材料H202产率和电芬顿催处理污染物的影响。另外,电催化应用领域的另一重要研究方面涉及工艺运行方式的选择与优化,本研究构建了双阴极旋转式电芬顿反应器,并考察运行中各种工艺参数的影响,主要结论如下：1.采用成本较低的乙醇和水合肼对石墨毡(软毡)材料进行改性。改性后石墨毡纤维表面附着有大量碳颗粒,材料表面的亲水性有所增强。XPS分析结果表明,水合肼在石墨毡材料表面引入含量约0.56at.%的氮元素,且以“石墨型氮”结构、吡啶型氮基团和不同的氮氧化物基团(如-NOx或N-O-C)形式存在；材料表面具有亲水性的含氧基团增多。与未改性的石墨毡阴极相比,经过改性的电极表现出更强的电流响应,析氢电位也向负电位方向移动,并且促进了ORR的电子传递动力学过程。化学改性提高了H202的产量,经过乙醇-水合肼改性的阴极CF-B系统中H202的产量最高,达到175.8mg/L。改性有利于改善电芬顿系统的催化氧化性能,矿化率最高达到51.4%,较改性前提高了29.2%。改性电极具有良好的稳定性,CF-B在第十次使用时,改性电极对p-Np的矿化率仍保持在45%以上。2.优化了化学改性石墨毡阴极产H2O2的主要影响因素。确定了最佳的水合肼组分浓度为10%,此时系统中H2O2的产量约为改性前的2.6倍。考察了不同阴极电位、初始pH和02曝气流量对H2O2产量与电流效率的影响,结果发现,在阴极电位-0.75V,pH为中性条件,O2曝气流量为0.4L/min的条件下,H2O2产量最高,约为247.2mg/L。电流效率随阴极电位的上升、pH的下降呈现下降趋势,此外,适宜的02曝气量的选择不仅能够促进系统中H202的生产过程,同时也能够有效节约运行成本。3.采用无毒、简单、快速的电化学氧化方法对石墨毡(硬毡)材料进行改性。材料表面O元素与C元素含量的比例(O/C)随着电化学氧化处理循环次数的增加而不断升高。与未改性的石墨毡材料相比,改性过程增加了材料表面的亲水性基团,有利于改善材料的亲水性能,而且经过阳极氧化处理的电极在相同电位下具有更强的电流响应,并且电流响应值随着电化学氧化循环次数的增加而明显增大,析氢电位也向负电位方向移动。与未改性的电极相比,改性使氧还原过程的激发电位(|E|)约正向偏移了约0.1V。电化学阳极氧化的最佳循环次数确定为10次,改性后系统对对硝基苯酚的矿化率提高了27.9%～35.3%。4.采用新型的双阴极转盘式电芬顿反应器进行H202的生产和电催化降解污染物的过程,通过对比静止和转动条件下的线性伏安扫描曲线,确定了转动过程对系统氧还原电流响应的促进作用。在0.05mM Na2SO4电解液中,施加电流为100mA,阴极转盘转速为10rpm,电解60min,系统内的H202浓度可达到108.1mg/L,电流效率为40.9%,H2O2产率约为转盘静止条件下的3倍。以染料甲基橙(MO)为目标污染物,考察了阴极转盘电芬顿系统中不同的Fe3+浓度、pH、支持电解质以及污染物初始浓度对系统催化效果的影响,结果发现,Fe3+在MO色度去除和TOC去除方面具有不同的作用,由于Fe3+会与偶氮染料发生络合作用,使偶氮显色基团更加稳定,脱色过程较不加Fe3+略有减缓,但是Fe3+加入后有利于系统TOC的去除,当Fe3+浓度为0.2mM时系统达到最佳的TOC的去除率,约为48.2%,与主要依靠直接电解和H2O2氧化作用的无Fe3+系统相比提高了26.6%。转盘式电芬顿反应系统与典型的电芬顿系统具有类似的pH条件要求,反应最佳的pH为3左右,在30min即可完全去除溶液中的色度。MO在不同电解液中的降解效果为NaNO3>NaCl>Na2SO4,且在NaNO3电解液中的矿化率可达到51.2%。更多还原

【Abstract】 Electro-Fenton technology (EF) is a new, efficient and clean electrochemical advanced oxidation technology, which has attracted a great deal of attention in recent years. Since the production of H2O2is significantly dependent on the cathodes used, which directly influence the degradation efficiencies of pollutants in EF system, developing new efficient cathodic materials becomes one of the research focuses in the area.In this study, the commercial graphite felts with three-dimensional structure were used as the pristine cathode materials, chemical and electrochemical modification methods were used to improve the catalytic activities of oxygen reduction reaction (ORR), and the effects of the modification on the production of H2O2and EF degradation efficiency were investigated on the basis of characterization. In addition, the other important aspect for the EF——the reactor was also discussed, and a new dual-cathode rotating disk EF reactor was developed, impacts of the operational parameters were also studied. The main conclusions can be drawn as follows:1. Low-cost chemical reagents ethanol and hydrazine hydrate were used to modify the graphite felts (soft felts). The XPS analysis showed that after modification, plenty of carbon particles appeared on the surface of graphite felt fibers, and the hydrophilicity of the materials was improved. Approximately0.56at.%nitrogen element was detected in the hydrazine hydrate-ethanol modified sample (CF-B) in the forms of "graphite nitrogen" structure, pyridine nitrogen groups and the type of nitrogen oxide groups (such as-NOx or NOC), and there were more hydrophilic groups. Compared with the unmodified cathode, the modified ones showed stronger current responses, more negative hydrogen evolution potentials, and the increased electron transfer kinetics for ORR process. The highest H2O2accumulation was achieved at CF-B, up to175.8mg/L. The modification could improve the performance of EF, and the highest mineralization ratio in modified cases was51.4%,29.2%higher than before. CF-B was detected above45%of the mineralization of p-Np after10cycles of use, indicating a good stability of the modified electrodes.2. The influencing factors during the production of H2O2were investigated at the chemically modified graphite felt electrodes. The optimal concentration of hydrazine hydrate in the chemical modification was determined as10%, when the yield of H2O2was approximately as2.6time as before. The influence of the cathode potentials, pH and O2flow rate on the H2O2production and current efficiency (CE) were also investigated. The highest H2O2accumulation was achieved at-0.75V, neutral pH and0.4L/min of O2flow rate, up to247.2mg/L. The CE tended to decrease with the increase of potentials and decrease of pH, and a suitable aeration amount of O2is not only to promote the production of H2O2, also could effectively reduce operating costs.3. A non-toxic, simple, rapid electrochemical modification, so call "anodisation", was used to modify the graphite felt materials (hard felts). The ratio between O and C (O/C) on the electrode surfaces was detected increasing with with the increase of the electrochemical oxidation treatment cycles. Compared with the pristine cathode, the hydrophilic groups increased on the modified surface, which was favorable to improve the hydrophilic properties of the materials. After anodisation, the cathodes had stronger current responses, which were significantly increased with the increase of the anodising cycle times, the hydrogen evolution potential was more negative, and the trigger potential of ORR at modified. cathodes was about0.1V more positive than pristine one. The optimum anodising cycle times was10, when the mineralization ratio of the/p-Np increased27.9%-35.3%.4. A new dual-cathode rotating disk EF reactor was used for H2O2production and electrocatalytic degradation of pollutants. The positive effects of the rotating conditions on the current responses toward ORR were determined by linear sweep voltammetry. The highest yields of H2O2was achieved at100mA, with rotating speed of10rpm, in0.05mM Na2SO4electrolyte, up to108.1mg/L, and the CE was40.9%, which was as3times as at static conditions. The operational parameters such as Fe3+concentration, pH, support electrolytes and initial concentration of pollutants on the catalytic performance of the rotating disk system were investigated using the Methyl Orange (MO) as a target pollutant. The different influences of Fe3+on the decoloration and mineralization was found, due to the complexation between Fe3+and azo dyes, the addition of Fe3+can make the chromophore more stable. However, the existence of Fe3+was conducive to the removal of TOC, and the optimum concentration of Fe3+was0.2mM, when the mineralization ratio was48.2%, which was26.6%higher than the system without Fe3+. The suitable pH in rotating disk reactor was similar with other EF systems, and the decoloration can be completed within30min at pH around3. The degradation efficiency of MO in different electrolytes followed the order NaNO3> NaCl> Na2SO4, and the mineralization ratio in NaNO3electrolyte was51.2%.更多还原