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电容去离子(capacitive deionization,CDI)因其具有低能耗和对环境影响小的优点而备受关注[1-3]。然而,传统的CDI存在吸附容量低和间歇运行的缺点。为克服这些缺陷,2013年由JEON等[4]首次提出了流动电极电容去离子(flow electrode capacitive deionization,FCDI)的技术。活性炭[5-6]、炭黑(carbon black,CB)[7]以及碳纳米管[8-10]等多孔碳材料被用作FCDI中的流动电极,而不是传统CDI中的固定电极。带电离子在电场下迁移,然后储存在表面带有相反电荷的流动电极中。由于不断有再生的流动电极补充到电极室,因此,FCDI能够进行连续脱盐[11-12]。然而,关于流动电极孔径分布对FCDI脱盐性能的影响的研究较少。在先前的研究中提到,增加流动电极的微孔面积可以有效地改善CDI电极的脱盐性能[13]。此外,也有研究[14]表明,较高的介孔率使离子更容易的进入电极/电解质界面。因此,流动电极的孔径分布对FCDI的脱盐性能的影响机制仍存在争议。
在本研究中,使用具有不同孔径和相同导电性的4种炭黑作为流动电极,比较了孔径分布对FCDI脱盐性能的影响,使用X射线光电子能谱(XPS)、傅里叶变换红外光谱(FT-IR)、X射线衍射(XRD)、拉曼光谱(Raman)和电化学阻抗谱(EIS)对流动电极的电子传递能力进行了表征,在2种操作模式下对FCDI脱盐效果进行了评估,并且使用吸附-解吸实验探究了微孔和介孔对离子的吸附和解吸速率的影响,以期为设计和选择具有最佳脱盐效果的流动电极提供参考。
炭黑流动电极的孔径分布对流动电极电容去离子脱盐性能的影响
Effect of pore size distribution of carbon black flow electrode on the desalination of flow electrode capacitive deionization
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摘要: 流动电极电容去离子(flow electrode capacitive deionization,FCDI)主要依靠流动电极的电吸附来实现离子去除。而其中流动电极的孔径分布是影响FCDI的脱盐性能的重要因素。为此,选择4种具有高导电性的炭黑(carbon black,CB)作为流动电极,考察了流动电极的孔径分布对FCDI脱盐性能的影响。结果表明,在隔离闭合循环(isolated closed-cycle,ICC)模式下,脱盐性能与流动电极的比表面积呈正相关(r=0.918),并主要受介孔面积的影响。在单循环(single cycle,SC)模式下,FCDI的脱盐性能与介孔面积呈正相关(r=0.583),与微孔面积呈负相关(r=-0.725)。当使用介孔面积最大的炭黑作为流动电极时,离子在流动电极表面的解吸速率升高了53%,FCDI的脱盐率提高了702%。吸附-解吸实验结果表明,由于微孔存在尺寸小、吸附-解吸路径长等缺点,使被流动电极吸附的离子难以被快速解吸,从而抑制了在SC模式下流动电极的再生。介孔可强化FCDI在2种操作模式下的脱盐性能;而微孔却抑制了SC模式下的离子解吸,从而降低了FCDI的脱盐性能。以上研究结果可为流动电极的设计和选择提供参考。Abstract: Flow electrode capacitive deionization (FCDI) mainly relies on the electro-adsorption of the flow electrode to realize ion removal. Among them, the pore size distribution of flow electrode is an important factor affecting the desalination performance of FCDI. Therefore, four kinds of carbon black (CB) with high conductivity were selected as flow electrodes, and the influence of pore size distribution of flow electrodes on the desalination performance of FCDI was investigated. The results showed that in the isolated closed-cycle (ICC) mode, the desalination performance was positively correlated with the specific surface area of the flow electrode (r=0.918), and was mainly affected by the mesoporous area. In the single cycle (SC) mode, the desalination performance of FCDI was positively correlated with mesopore area (r=0.583) and negatively correlated with micropore area (r=-0.725). When carbon black with the largest mesoporous area was used as the flow electrode, the desorption rate of ions on the surface of the flow electrode increased by 53%, and the desalination rate of FCDI increased by 702%. The results of adsorption-desorption experiments showed that due to weakness of micropores such as small size and long path for adsorption-desorption, the rapid desorption for the ions absorbed by the flow electrode was difficult, which inhibited the regeneration of the flow electrode in SC mode. Mesopores could strengthen the desalination performance of FCDI in two operation modes, while micropore limited the desorption of ions in SC mode and the desalination performance of FCDI was weakened. The results can provide a reference for design and selection of the flow electrode.
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表 1 流动电极的比表面积和孔径分布与FCDI脱盐性能的相关性
Table 1. Correlation between specific surface area and pore distribution on FCDI desalination performance
运行模式 微孔/(m2·g−1) 介孔/(m2·g−1) 比表面积/(m2·g−1) 外表面积/(m2·g−1) r P r P r P r P ICC 0.391 0.209 0.842** 0.001 0.918** 0 0.650* 0.022 SC −0.725** 0.008 0.583* 0.047 −0.073 0.822 −0.279 0.379 注: r是皮尔逊相关系数,P是显著性指数,*表示P<0.05水平上显著;**表示P<0.01水平上显著。 -
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