WORCESTER BOSCH SET OF ELECTRODES 87186643010

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R i and R j are calculated by dividing the effluent concentration by feed concentration of each ion. E. N. Guyes, A. N. Shocron, A. Simanovski, P. M. Biesheuvel and M. E. Suss, Desalination, 2017, 415, 8–13 CAS.

K. Singh, S. Porada, H. D. de Gier, P. M. Biesheuvel and L. C. P. M. de Smet, Desalination, 2019, 455, 115–134 CrossRef CAS. In summary, the use of various electrode material, operational conditions, and surface modifications for selective ion separation was reviewed in this section. Thus, it is evident that electrodes can act as selective elements in CDI processes. In the following section, we will review the use of membranes for selective ion separation in CDI. 3. Membranes for ion selectivity In the previous section, ion selectivity in terms of electrodes was discussed. The use of membranes also plays a vital role in CDI. This section is dedicated for exploring the studies which rely on membranes for achieving ion selectivity. 3.1 Cation selectivity Several different studies have demonstrated the advantages of using IEMs to prevent co-ion repulsion, reduce anode oxidation, and to boost the salt removal by employing gradient of solutions in multi-chamber cells. 7,114 An IEM can also be used as a barrier for specific ions, and therefore, improve the ion selectivity.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.

The works of Eliad et al, Gabelich et al., and later of Huang et al., provided evidence on electrosorption behavior of different anions on porous carbon electrodes. They demonstrated that CDI could be used to selectively remove different species of ions from aqueous solutions. However, at this early stage of ion selectivity with CDI, some questions regarding the parameters involved and the accurate mechanisms behind the selectivity, still remained unanswered. 68 Flow-electrode CDI. In a recent addition to the set of CDI systems, flow-electrode capacitive deionization (FCDI) was invented to solve the persistent issue of the finite adsorption capacity of standard CDI cell designs. 81 In FCDI, a carbon slurry flows through channels between the current collector and IEM, continuously replenishing the capacitive material and eliminating the need for the regeneration step that pauses desalination ( Fig. 3b). Various closed-systems, in which the slurry is continuously discharged and re-used without pausing the desalting step, have been demonstrated. 82,83 Because the electrode material is continuously regenerated at a rate set by the electrode flow speed, performance metrics such as electrode capacity become less important; the limiting factor for FCDI, as shown in recent studies, is instead electrode conductivity. Fig. 3 Configurations of the cells used in (A) CDI, (B) intercalation-CDI, (C) flow-CDI, and (D) membrane-CDI. The selectivity elements of the cell, namely the electrodes in (A) and (B) and the membranes in (C) and (D) are highlighted in red. Per panel, relative salt concentrations are indicated with tones of blue. S. Samatya, N. Kabay, Ü. Yüksel, M. Arda and M. Yüksel, React. Funct. Polym., 2006, 66, 1206–1214 CrossRef CAS.

Abstract

T. Rijnaarts, D. M. Reurink, F. Radmanesh, W. M. de Vos and K. Nijmeijer, J. Membr. Sci., 2019, 570–571, 513–521 CrossRef CAS. R. Chen, H. Tanaka, T. Kawamoto, M. Asai, C. Fukushima, H. Na, M. Kurihara, M. Watanabe, M. Arisaka and T. Nankawa, Electrochim. Acta, 2013, 87, 119–125 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. Mrs Sevil Sahin received her BSc degree from the Department of Chemistry at Istanbul Technical University, and her MSc degree from the Department of Pharmaceutical Chemistry at Istanbul University, Turkey. During her MSc research, she synthesized porphyrin derivatives for photodynamic therapy. Since 2017, she is a PhD candidate in the Department of Organic Chemistry at Wageningen University, The Netherlands. Her doctoral research includes, among others, the use of polyelectrolyte multilayers for tuning ion selectivity in capacitive deionization.

M. Tedesco, H. V. M. Hamelers and P. M. Biesheuvel, J. Membr. Sci., 2018, 565, 480–487 CrossRef CAS.Akin to the work of Yeo et al., Zuo et al. investigated the viability of a resin to selectively remove sulfate from a mixture with chloride. 131 An experiment with the pristine high surface area carbon electrode demonstrated a higher selectivity towards chloride than sulfate ( S i/ j = 2.2), in agreement with the work of Sun et al. 75 The authors were able to reverse the selectivity (SO 4 2−/Cl − of 2.4) by coating the activated carbon electrode with the selective resin. The resin-coated carbon was able to maintain the selectivity of 1.9 towards sulfate even upon increasing the chloride concentration by a factor of 100. In contrast to some of the studies using nitrate-selective resins, 129,130 the authors did not report any issue during the desorption of the electrosorbed sulfate anions. P. Ratajczak, M. E. Suss, F. Kaasik and F. Béguin, Energy Storage Mater., 2019, 16, 126–145 CrossRef. Fig. 8 Generalized selectivity mechanisms in MCDI based on (A) selective resins, (B) charge repulsion, and (C) ion diffusion in membranes. c School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Daehak-dong, Gwanak-gu, Seoul 151-742, Republic of Korea