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题名: Pd-In双金属电极材料制备及催化电还原水中消毒副产物的研究
作者: 刘焰真1
学位类别: 硕士
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: 刘会娟 ; 兰华春
关键词: Pd-In双金属 ; 电化学还原 ; electroreduction ; 三维电极 ; three-dimensional particle electrodes ; 溴酸盐 ; bromate ; TCAA ; TCAA ; Pd-In bimetal
其他题名: The synthesis of Pd-In bimetal electrode materials and their application in electrochemical reduction of disinfection by-products
学位专业: 环境工程
中文摘要: 电化学方法可有效去除水中消毒副产物三氯乙酸(TCAA)、溴酸盐(BrO3)-, 因其环境友好、工艺简单、不引入新污染物而具有较好的应用前景。电化学还原 消毒副产物包括直接电子还原和间接原子氢 H*还原两个过程,因此加速电子转 移、增加原子氢 H*含量是提高电化学还原效率的关键。相比于传统的二维电化 学反应过程,三维粒子电极的加入,可有效提高电子的转移效率。Pd 金属因其 独特的电子构型,有利于电化学催化生成原子氢 H*还原目标污染物。并且,Pd 基催化剂的产氢性能和催化性能,可通过加入有效的助金属催化剂 In 来提升。 因此,本文利用共沉淀法合成 Pd-In双金属材料,考察其对溴酸盐的电化学去除 效果,并利用三维电极反应器,研究了其对 TCAA的处理效果和作用机制。 (1)通过共沉淀法合成 Pd-In/C双金属电极,用于 BrO3-的电化学连续去除。 随着 In的加入,Pd-In/C对 BrO3的催化活性逐渐提升,Pd-In原子比为 1:4时, 其对 BrO3-的电催化还原能力最好,可将 BrO3-高效还原为 Br-。In的加入,提高 了 Pd1-In4/C中 Pd、In的分散性,降低了与原子氢 H*生成有关的 Pd颗粒的团聚。 并且,与单金属 Pd 催化电极相比,Pd1-In4/C 中金属 Pd 更富电子,有利于原子 氢 H*的生成。此外,Pd1-In4/C在所有Pd基电极中表面 Zeta电位最高,且为正电,可促进电极表面吸附 BrO3-的还原活 。与 Pd/C相比,Pd1-In4/C电极对 BrO3-的还原活性提高了 7%,比纯 C电极提高了33%。连续 30天的实验室连续运行处理发现, Pd1-In4/C电极在 0.9 mA/cm2 ,水力停留时间 20 min条件下,10μg/L,可以对初始浓度约 23 μg/L的BrO3- 实现低能耗(0.21 Kw•h/t)、高效率(91%)的连续、稳定有效去除。 (2)合成了不同 Pd:In 比例的 Pd-In/Al2O3双金属粒子电极,在三维电极反 应体系,考察了其对 TCAA的还原效果。随着 In的加入,Pd-In/Al2O3对 TCAA 的催化活性先增加后降低,在 Pd-In原子比为 1:1时,其对 TCAA催化还原能力 最强,且还原过程满足准一级反应动力学。初始浓度为 500 μg•L -1的 TCAA,在 低电流密度(0.9 mA•cm-2 )条件下,30 min 内即可去除 94%的 TCAA。并且, 在相同实验条件下,Pd/Al2O3催化剂只能将 TCAA 还原为二氯乙酸(DCAA), 而 Pd-In/Al2O3则可以将其进一步还原为一氯乙酸(MCAA)。依据原子氢 H*掩 蔽实验,TCAA电还原过程中同时存在直接电子还原和间接原子氢 H*还原过程。 原子氢掩蔽实验表明,In的加入,增强了间接原子 H *还原过程,并且是 TCAA 还原的主要过程。XPS分析表明,Pd-In/Al2O3催化剂在 In加入后,金属 Pd以富 电子形式存在,提高了溶液中原子 H*的含量,ESR的信号更直观的证实了这一 点。此外,In 的加入,也增强了直接电子转移过程,在 TCAA 电化学去除过程 中,表现出明显的 Pd-In协同效应。
英文摘要: Electrochemical reduction treatment can effectively remove the disinfection by-product like trichloroacetic acid (TCAA) and bromate. As this method was environmental friendly, easy to operate, and do not introduce new pollutants, it become a very promising method nowadays. Both direct electron reduction and indirect atomic hydrogen H * reduction are involved in the electroreduction process. So, acceleration of electron transfer or enhancement of the concentration of atomic H* can significantly improve the electrochemical dechlorination process. Compared with the traditional two-dimensional electrochemical reaction process, the addition of the three-dimensional particle electrodes can effectively improve the electron transfer efficiency. Palladium catalysts have the unique property of simultaneously catalyzing the production of atomic H* and reducing target pollutants. Moreover these abilities could be promoted efficiently by the addition of indium, which acting as a promoter metal. Herein, bimetallic Pd–In electrocatalysts were synthesized via the coprecipitation method in this paper. And the effect of Pd-In bimetallic cathode on the electroreduction of bromate was investigated. The mechanism of Pd-In bimetallic particle electrodes on the removal of TCAA in a three-dimensional electrochemical reactor was also examined. (1) Bimetallic Pd–In/C cathode were synthesized and used for bromate electrochemical reduction. Bromate removal efficiency improved gradually with the increasing of atomic ratio of In to Pd, and a maximum value was achieved when In to Pd atomic ratio equals 4:1. Adding proper amount of In could avoid the aggregation of metals, and the dispersibility of Pd and In had also been improved simultaneously. As confirmed by the surface Zeta potential analysis, the surface charge of Pd1-In4/C was the highest among the Pd-In electrodes, and the positively charged surface was beneficial for bromate adsorption. Morever, the metallic Pd existed in a more electron-rich state in Pd1-In4/C, improving the atomic H* formation process. Comparing with C electrode, the bromate reduction efficiency increased by 26% via Pd/C cathode, and another 7% removal efficiency was achieved when using Pd1-In4/C cathode. In a 30 days’ consecutive electrochemical process, Pd1-In4/C exerts a very stable and efficient reduction ability. Bromate with the initial concentration of 23 μg/L could be reduced effectively with only 20 min hydraulic retention time at 0.9 mA/cm current density, consuming only 0.21 Kw•h/t electricity. Bromate was totally reduced to Br along the electroreduction process. (2) Pd-In electrocatalysts were evenly deposited on an Al2O3 substrate, and XRD,TEM, XPS analyses confirmed the formation of Pd-In bimetal. Electrochemical removal of TCAA by the Pd-In/Al2O3 catalyst was performed in a three-dimensional reactor, and all the reduction processes were shown to follow pseudo-first order kinetics. The removal efficiency of TCAA by Pd-based catalysts was increased to a maximum value, and then decreased with increasing atomic ratio of In to Pd. While In/Al2O3 showed almost no activity for TCAA reduction, 94% of TCAA with the initial concentration of 500 μg/L could be reduced in 30 min by Pd-In/Al2O3 (atomic ratio = 1:1) under a relatively low current density (0.9 mA/cm2 ), showing the highest electrochemical activity towards TCAA removal. In contrast to the final reduction product of dichloroacetic acid (DCAA) found in the Pd/Al2O3 system, TCAA and DCAA could be further reduced to monochloroacetic acid (MCAA) using Pd-In/Al2O3 catalysts. According to scavenger experiments, an electron transfer process and atomic H* formation function both existed in the TCAA reduction process, and the enhanced indirect atomic H* reduction process (confirmed by ESR signals) played a chief role in the TCAA removal. As confirmed by XPS analysis, the metallic Pd existed in a more electron-rich state in Pd-In/Al2O3, which was beneficial for atomic H* formation. Moreover, the synergistic effects of Pd and In were proven to be able to enhance both direct electron transfer and indirect atomic H* formation, indicating a promising prospect for bimetallic electrochemical reduction treatment.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38670
Appears in Collections:环境水质学国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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