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.
Highlights
The growing global population, causing a high demand for water that outpace supply, and water pollution due to industrialization, have led to water shortage and, driven the need for water purification [1]
To understand the underlying mechanism of ion rejection by electrostatic interactions, we experimentally investigated the influence of surface zeta potential (SZP) on the formation of the ion depletion zone (IDZ)
For the highly negatively charged membrane with SZP value of −97.5 mV (Case C), the fluorescent intensity increased from 0 to 340 up to the axial position of approximately 350 μm. These findings indicated that the formation of IDZ along the axial was largely affected by the channel depth and membrane SZP values
Summary
The growing global population, causing a high demand for water that outpace supply, and water pollution due to industrialization, have led to water shortage and, driven the need for water purification [1]. While plants need water as an essential element for various metabolic activities [3], some offer an interesting advantage of water filtration ability [4,5,6]. We investigated water filtration distinctive features of the mangroves, among them, the surface zeta potential (SZP) of root which we found to be approximately −91.4 mV. This SZP value is noticeably higher than those of conventional water filtration membranes [9]. The validity of this hypothesis has not been examined in detail yet
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