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题名: Pd/石墨烯阴极电催化原子氢还原去除水中消毒副产物机制
作者: 冒冉1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 曲久辉 ; 赵旭
关键词: 溴酸盐,三氯乙酸,电催化还原,原子 H*,Pd/rGO/CFP电极,GR-Cu ; bromate, trichloroacetic acid, electrocatalytic reduction, atomic H*, Pd/rGO/CFP electrode, GR-Cu foam electrode foam电极
其他题名: Electrochemical reductive removal of desinfection byproducts via atomic hydrogen at Pd/graphene cathodes
学位专业: 环境工程
中文摘要: 溴酸盐(BrO3-)和卤乙酸(HAAs)是饮用水中常见的消毒副产物,对人体 具有潜在的致癌性。电化学还原去除卤代有机物技术由于反应速率快,反应条件 温和,可有效减少化学品投加和二次污染而受到越来越多的关注。然而,常用的 阴极电还原污染物所需阴极负电位较高,易发生析 H2副反应,导致电流效率降 低。因此,开发可在低电位下具有高电催化还原活性的阴极材料,并揭示污染物 的电催化还原微观机制,是提高电流效率、实现污染物高效去除的关键之一。围 绕上述关键技术问题,本论文开展了如下研究工作: 1、研制出具有高电催化活性并可显著降低污染物还原过电位的钯(Pd)/石 墨烯(rGO)复合电极。以碳纤维(CFP)材料为基底,通过化学还原和电沉积 方法分别负载 rGO和 Pd,制得 Pd/rGO/CFP电极。在 -0.5 V的低电位下, Pd/rGO/CFP电极在 40 min内对 BrO3-去除率达到 98.7%。rGO促进了原子 H*的 还原至 Br-。且由于 rGO表面含氧基团和产生从而通过间接原子 H*还原将 BrO3- Pd之间的化学作用,复合电极具有很好的稳定性。 2、研究了 Pd/rGO/CFP电极电催化还原三氯乙酸(TCAA)脱氯过程中原子 H*的产生及作用机制。首次通过电子自旋共振(ESR)技术研究了 Pd/rGO/CFP、 CFP、rGO/CFP和 Pd/CFP电极产原子 H*过电位。在 Pd/rGO/CFP电极表面原子 H*更容易产生,其产 H*过电位正于其它三种电极 0.4-1.0 V。对于 Pd/CFP和 Pd/rGO/CFP电极,原子 H*是主要活性物种,表明间接还原机制在脱氯过程中起 到了决定作用;而对于 CFP和 rGO/CFP电极,直接电子还原是 TCAA主要脱氯 机制。在实验基础上,结合密度泛函理论计算揭示了 Pd/rGO/CFP电极通过电子 耦合作用强化产氢机制,且 rGO的引入可以强化固氢,其优异的产氢固氢特性 决定了其高电催化还原活性。 3、制备出无贵金属的新型 3D石墨烯/泡沫铜(GR-Cu foam)电极,成功应 用于电催化 TCAA脱氯。3D GR显著促进了 TCAA还原转化并提高了协同脱氯 路径所占比例。Cu foam电极电还原 TCAA在酸性条件下得到促进,而 GR-Cu foam电极电还原 TCAA受 pH影响较小且可抑制 Cu溶出。Cu foam和 GR-Cu foam电极体系的 TCAA脱氯机制均以直接阴极还原为主,但是 3D GR的存在会 提高 GR-Cu foam体系对原子 H*的储存能力从而促进脱卤反应。在处理含 HAAs 饮用水时,GR-Cu foam电极具有较好的稳定性并可重复使用。 4、设计了三维电极连续流电化学反应器,显著提高了反应器极水比,成功 应用于自来水低浓度 BrO3-的电还原去除。研制出 Pd/rGO共修饰颗粒活性炭(Pd-rGO/GAC)作为阴极室感应粒子电极,Pd/rGO/CFP电极作为主阴极。结果表明粒子电极和主阴极可协同产原子 H*,从而高效催化还原 BrO3-。在电流密度为 0.9mA/cm2,水力停留时间为 20 min条件下,BrO3-由 20 μg/L降至 6.6 μg/L。尽管水中 Ca2+、Mg2+会产生沉淀覆盖在Pd催化剂表面,反应器仍可在 30天连续运行中保持较高的催化活性,且沉淀物主要覆盖在 Pd/rGO/CFP主阴极表面,对 Pd-rGO/GAC表面影响很小。该电化学体系在消减特定条件实际水体中 BrO3-及其它污染物方面具有较好的应用前景。
英文摘要: Bromate (BrO3-) and haloacetic acids (HAAs) are commonly detected disinfection byproducts in water and known to have suspected human carcinogenicity. Due to its rapid reaction rate, mild reaction conditions, and efficient minimization of toxic chemicals and secondary pollution, interest in the application of electrochemical reductive treatments to remove halogenated organic compounds is growing. However, the reduction of many pollutants at the most commonly used cathodes occurs at very negative potentials, where strong reduction of water may take place, resulting in vigorous H2 evolution and a drastic increase of electrical energy consumption. Therefore, it is desirable to develop new electrode materials with excellent catalytic properties in the reductive reactions at low cathode potentials and uncover the underlying mechanisms. The main contents and results of this paper were as follows. (1) A novel Pd/reduced graphene oxide (rGO) composite electrode with a high electrocatalytic activity was fabricated on carbon fiber paper (CFP) via chemical reduction and a subsequent electrodeposition process, which can significantly decrease the cathode reduction potential of pollutants. With the Pd/rGO/CFP electrode, the removal efficiency of BrO3- is up to 98.7% within 40 min at -0.5 V. The rGO sheets to Br- . Due to promoted the production of atomic H* for the indirect reduction of BrO3- the strong interaction between surface oxides of rGO and Pd, the high stability of the composite film electrode is exhibited. (2) The production and role of atomic H* at the Pd/rGO/CFP electrode for a electrochemical dechlorination process taking trichloroacetic acid (TCAA) as a target pollutant was investigated. The onset overpotentials for atomic H* production at the Pd/rGO/CFP, CFP, rGO/CFP, and Pd/CFP electrodes were first reported by using electron spin resonance (ESR). The production of atomic H* at the Pd/rGO/CFP electrode was more favorable than that at the other three electrodes, resulting in a 0.4- 1.0 V more positive overpotential for atomic H* production. Atomic H* was the main active species for Pd/CFP and Pd/rGO/CFP electrodes, while direct electron reduction was responsible for TCAA dechlorination at CFP and rGO/CFP electrodes. On the basis of the experimental and computational results, the superior catalytic activity of the Pd/rGO/CFP electrode was ascribed to the presence of synergistic effects, including the enhanced production of H* stemming from electronic coupling between Pd and rGO sheets and the unique ability of the rGO-supported Pd particles to adsorb atomic H*. (3) A noble metal-free 3D GR-Cu foam electrode was fabricated and successfully applied in TCAA dechlorination. The results showed that the 3D GR on Cu foam significantly facilitated the reductive transformation and promoted the concerted dechlorination pathway. TCAA dechlorination at the Cu foam electrode was enhanced at acidic pH, while a slight pH effect was observed at the GR-Cu foam electrode with a significant inhibition for Cu leaching. The direct reduction by electrons was responsible for TCAA dechlorination at both Cu foam and GR-Cu foam electrodes, while at GR-Cu foam electrode, the surface-adsorbed atomic H* also contributed to TCAA dechlorination owing to the chemical storage of hydrogen in the GR structure. Finally, the feasibility of the electrochemical reductive treatment of HAAs- contaminated drinking water, and stability of the electrode in the repeated applications were also demonstrated. (4) A continuous three-dimensional (3D) electrochemical reactor was established to increase the A/V ratio for the removal of BrO3- with a typical concentration in tap water treatment. The Pd-rGO modified granular activated carbon (Pd-rGO/GAC) was prepared for the first time and was used as particle electrode for the cathode cell. The Pd/rGO/CFP electrode was used as the cathode. The results showed that the combination of the Pd/rGO/CFP cathode and Pd-rGO/GAC particles resulted in a synergism in the production of atomic H* and thus a high activity toward BrO3- removal. Under the current density of 0.9 mA/cm2 , BrO3- with the initial concentration of 20 μg/L was reduced to be less than 6.6 μg/L at the HRT of 20 min. Although the precipitates generated from Ca2+ and Mg2+ in the tap water would cover the Pd catalysts, a long- lasting electrocatalytic activity could be maintained for the 30 d treatment. The precipitates were predominantly deposited onto the Pd/rGO/CFP cathode rather than the Pd-rGO/GAC particles. The findings indicate that the 3D electrochemical reactor may serve as a promising system for BrO3- reduction or other catalytic reduction of contaminants in water treatment.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38678
Appears in Collections:环境水质学国家重点实验室_学位论文

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