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. 2021 Apr 28;16(4):e0250343.
doi: 10.1371/journal.pone.0250343. eCollection 2021.

Migration of ions near charged surface

Kiwoong Kim  1
Affiliations

Migration of ions near charged surface

Kiwoong Kim. PLoS One. .

Abstract

Detailed understanding of ionic behavior in the region near a charged surface is important for the enhancement of water filtration mechanisms. In this study, a highly charged membrane is hypothesized to form an ion depletion zone (IDZ) without an external power supply. The formation of IDZ was experimentally investigated using membranes with varying surface zeta potential (SZP) values to confirm the hypothesis. The surface zeta potential of the charged membrane was controlled by layer-by-layer deposition method. Our results indicate that indicated that the fluorescent intensity near the charged surface becomes weaker with an increased absolute magnitude of SZP. Ionic surfactants enhance the formation of IDZ by increasing SZP magnitude, and by forming a secondary filtration layer. These findings provide information that is helpful in understanding the ionic behavior near the highly charged surface. In addition, the information provided by the findings would be helpful in fabricating a small-scale water filtration device.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Formation of IDZ according to SZP of a membrane.
Schematics illustrating IDZ formation around the membrane. Cations (red circle) are attracted toward a negatively charged surface, whereas anions (green circle) are repelled from the surface of a moderately charged membrane (yellow square) when the membrane is exposed to an ionic solution. Ion depletion zone is rarely formed in this case. However, when a highly negatively charged membrane (orange square) is exposed to the ionic solution, formation of IDZ (white area) is enhanced.
Fig 2
Fig 2. A schematic of the experimental setup.
(A) Two microchannels with a width of 500 μm in width and depths of 55 and 10 μm were fabricated. Three membranes with different SZP values were inserted between a slide glass and the PDMS channel. (B) The PDMS channel and the slide glass were bonded using O2 plasma etching. The feed solution containing an ionic solution and fluorescent dyes were supplied to the inlet, and behaviors of fluorescent dyes were observed using an inverted microscope. (C) A cross-sectional view of the experimental setup.
Fig 3
Fig 3. Variations of IDZ intensity formed near the charged membrane.
The fluorescent intensity of sum of PFD and NFD was analyzed using three membranes with different SZP Magnitude. The fluorescent profile was calculated using the membrane marked by the green arrow. Formation of IDZ means ion depleted solution compared to feed solution is obtained. This result indicated the concentration distribution along the microchannels (A) a 55 μm and (B) a 10 μm.
Fig 4
Fig 4. Formation of IDZ near the charged membranes.
(A) The normalized fluorescent intensities of PFD and NFD were measured, respectively. (B) The IDZ area defined as the region whose intensity was lower than 220 was calculated.
Fig 5
Fig 5. Effect of ionic surfactant on normalized intensity.
(A) A schematic of SDS molecules adsorption on the negatively charged membrane surface. (B) Variation in normalized fluorescent intensity according to SDS concentration.
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References

    1. Ren D., Yang Y., Yang Y., Richards K., Zhou X., Land-Water-Food Nexus and indications of crop adjustment for water shortage solution, Sci. Total Environ., 626 (2018) 11–21. 10.1016/j.scitotenv.2018.01.071 - DOI - PubMed
    1. Ashbolt N.J., Microbial contamination of drinking water and disease outcomes in developing regions, Toxicology, 198 (2004) 229–238. 10.1016/j.tox.2004.01.030 - DOI - PMC - PubMed
    1. Wullschleger S.D., Meinzer F., Vertessy R., A review of whole-plant water use studies in tree, Tree physiology, 18 (1998) 499–512. 10.1093/treephys/18.8-9.499 - DOI - PubMed
    1. Khan M.A., Ungar I.A., Showalter A.M., The effect of salinity on the growth, water status, and ion content of a leaf succulent perennial halophyte, Suaeda fruticosa (L.) Forssk, J. Arid Environ., 45 (2000) 73–84.
    1. Webb J., Quinta R., Papadimitriou S., Norman L., Rigby M., Thomas D., et al.. Halophyte filter beds for treatment of saline wastewater from aquaculture, Water Res., 46 (2012) 5102–5114. 10.1016/j.watres.2012.06.034 - DOI - PubMed

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Grants and funding

This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (NRF-2020R1C1C1003813).

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