WORCESTER BOSCH SET OF ELECTRODES 87186643010

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W. Shi, X. Zhou, J. Li, E. R. Meshot, A. D. Taylor, S. Hu, J. H. Kim, M. Elimelech and D. L. Plata, Environ. Sci. Technol. Lett., 2018, 5, 692–700 CrossRef CAS. S. Sahin, J. E. Dykstra, H. Zuilhof, R. L. Zornitta and L. C. P. M. de Smet, ACS Appl. Mater. Interfaces, 2020, 12, 34746–34754 CrossRef CAS. S. Buczek, M. L. Barsoum, S. Uzun, N. Kurra, R. Andris, E. Pomerantseva, K. A. Mahmoud and Y. Gogotsi, Energy Environ. Mater., 2020, 3, 398–404 CrossRef CAS. J. Pan, Y. Zheng, J. Ding, C. Gao, B. van der Bruggen and J. Shen, Ind. Eng. Chem. Res., 2018, 57, 7048–7053 CrossRef CAS.

P. M. Biesheuvel, S. Porada, M. Levi and M. Z. Bazant, J. Solid State Electrochem., 2014, 18, 1365–1376 CrossRef CAS. C. J. Gabelich, T. D. Tran and I. H. Suffet, Environ. Sci. Technol., 2002, 36, 3010–3019 CrossRef CAS. W. Xing, J. Liang, W. Tang, G. Zeng, X. Wang, X. Li, L. Jiang, Y. Luo, X. Li, N. Tang and M. Huang, Chem. Eng. J., 2019, 361, 209–218 CrossRef CAS. S. Samatya, N. Kabay, Ü. Yüksel, M. Arda and M. Yüksel, React. Funct. Polym., 2006, 66, 1206–1214 CrossRef CAS. D. I. Oyarzun, A. Hemmatifar, J. W. Palko, M. Stadermann and J. G. Santiago, Water Res.: X, 2018, 1, 100008 Search PubMed.c School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Daehak-dong, Gwanak-gu, Seoul 151-742, Republic of Korea Dynamic calculations by Zhao et al. using porous electrode theory for mono/di cation mixtures, with monovalent anions, showed that an electrode that initially selectively adsorbed monovalent cations, switched to the adsorption of divalent cations and desorption of the adsorbed monovalent cations later in the process, in line with experimental observations. Also, in Zhao et al., Gouy–Chapman–Stern (GCS) theory was used for mono/di cation mixtures containing the same monovalent anion, and combined with a model that describes ion transport to a planar charged wall. This model qualitatively showed the same phenomenon of replacement of monovalent cations by divalent cations during prolonged charging of the electrode. Finally, Zhao et al. summarized relevant equations for the GCS model for the excess ion adsorption in an EDL in mono/di cation mixtures (or, equivalently, for mono/di anion mixtures containing the same monovalent cation). For the GCS model, these equations did not yet exist for a three-ion mixture, and therefore they extended the existing classical expressions for binary ion mixtures, such as mono/di cation mixtures with the same monovalent anion. 143,144 Iglesias et al. 145 combined a simple transport model for mono/di cation mixtures with an mD model, and also combined it with a model based on the Poisson–Boltzmann equation including the permanent fixed charges (their Fig. 4B) to describe ion adsorption. A similar Poisson–Boltzmann calculation including salt mixtures was developed for the reverse of CDI, the controlled mixing of salt and fresh water, by Fernandez et al. 146 and by Jimenez et al. 147 who included ion-volume effects as well. Moving forward, research into new electrode materials and chemistries, modification and optimization of existing materials, investigation of parameters in selectivity operation, modeling of selectivity at the system and molecular level, and finally, techno-economic analysis into the viability of selective ion separation via CDI will be crucial for fully realizing the potential of ion-selectivity via CDI. S. Choi, B. Chang, S. Kim, J. Lee, J. Yoon and J. W. Choi, Adv. Funct. Mater., 2018, 28, 1–9 Search PubMed.

Activated carbon. Activated carbon, defined by its high surface area to volume ratio, was used in the first CDI system 16 developed in the 1960's; in recent years this material has been modified to achieve even higher surface areas and hierarchical pore geometries with fast charge transfer and ion diffusion kinetics. In general, activated carbon, comprised of aggregates of microporous particles, is fabricated through pyrolysis of a carbon precursor, such as wood, then is activated ( i.e. micropores are created) via chemical etching or gasification of the product. 45 Although the typical performance of activated carbon electrodes does not match those of 1D and 2D materials (see Fig. 8a for a comparison), the low cost of activated carbon makes it an appealing electrode material for commercial applications. 47,48 In an electrode, the Donnan potential can be modulated by changing the cell voltage between two electrodes, or by changing the bulk electrolyte composition. By contrast, for a given IEM, the Donnan potential depends solely on electrolyte composition. 157 Both for electrodes and membranes, the charge density in the confined pore geometry is of importance, and in the Donnan approach this is defined per volume of micropores, thus has unit C m −3 or mol m −3 = mM. We will denote micropore charge with the symbol σ 0 with unit mol m −3. It can be multiplied by Faraday's number, F, and the microporosity to obtain the charge per volume of total electrode. This electronic charge σ 0 can be changed from negative to positive in carbon micropores, to adsorb either cations or anions, respectively. Meanwhile, in some other materials, such as PBA, an intercalation material, the charge is very negative and so, this material only absorbs cations. 78 On this count it resembles a subset of IEMs containing negatively charged groups, such as sulfonic groups, known as CEMs. Unlike in CEMs, in PBA the negative charge can be modulated up or down via injection or removal of electronic charge. Y. Gao, L. Pan, H. B. Li, Y. Zhang, Z. Zhang, Y. Chen and Z. Sun, Thin Solid Films, 2009, 517, 1616–1619 CrossRef CAS. M. Tedesco, H. V. M. Hamelers and P. M. Biesheuvel, J. Membr. Sci., 2016, 510, 370–381 CrossRef CAS. S. Jeon, H. Park, J. Yeo, S. Yang, C. H. Cho, M. H. Han and D. K. Kim, Energy Environ. Sci., 2013, 6, 1471–1475 RSC.S. Mao, L. Chen, Y. Zhang, Z. Li, Z. Ni, Z. Sun and R. Zhao, J. Colloid Interface Sci., 2019, 544, 321–328 CrossRef CAS. For an ionic mixture with ions of all possible valencies z, typically ranging between −2 and +2, an overall micropore charge balance is Recently, Zhang et al. used activated carbon in flow CDI to selectively remove Cu 2+ from a solution which also contained Na +. 65 A higher affinity towards Cu 2+ was obtained in the system. This was attributed to the preferential adsorption of Cu 2+ on the carbon particles and was also reduced to Cu. The preference of carbon towards divalent over monovalent cations, as shown in Fig. 6A was also reported here. The Na + removed from the feed remained in the electrolyte of the flow electrode.

J. E. Dykstra, R. Zhao, P. M. Biesheuvel and A. Van der Wal, Water Res., 2016, 88, 358–370 CrossRef CAS. S. P. Hong, H. Yoon, J. Lee, C. Kim, S. Kim, J. Lee, C. Lee and J. Yoon, J. Colloid Interface Sci., 2020, 564, 1–7 CrossRef CAS. The effect of operational conditions on anion selectivity was explored in MCDI processes. Hassanvand et al. compared the electrosorption performance of MCDI with CDI using multicomponent solutions. 53 Compared to MCDI, CDI showed a lower nitrate removal than chloride, and a lower charge efficiency. Simultaneously, the presence of inverse peaks, which is caused by co-ion repulsion, was also observed during nitrate removal. Since nitrate has a high affinity to the carbon surface (both hydrophobic), nitrate accumulates on its surface being then repelled during the cathodic polarization, which was also reported by Mubita et al. The inversion peak disappeared by using an AEM, as already reported in literature, 7,135 and the removal of nitrate and chloride as well as their charge efficiencies became similar. At the same time, the removal of sulfate was lower than that of chloride and nitrate in CDI as well as MCDI. The use of an AEM resulted in a faster sulfate desorption even though the monovalent ions were preferred during the adsorption. A possible explanation of this observation provided by the authors is that a part of the sulfate ions were retained in the membrane surface, and therefore, the path length during the desorption was much shorter compared to that of monovalent ions. Y. Liu, W. Ma, Z. Cheng, J. Xu, R. Wang and X. Gang, Desalination, 2013, 326, 109–114 CrossRef CAS.

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R i and R j are calculated by dividing the effluent concentration by feed concentration of each ion.