Capillarity ion concentration polarization as spontaneous desalting mechanism

Abstract

To overcome a world-wide water shortage problem, numerous desalination methods have been developed with state-of-the-art power efficiency. Here we propose a spontaneous desalting mechanism referred to as the capillarity ion concentration polarization. An ion-depletion zone is spontaneously formed near a nanoporous material by the permselective ion transportation driven by the capillarity of the material, in contrast to electrokinetic ion concentration polarization which achieves the same ion-depletion zone by an external d.c. bias. This capillarity ion concentration polarization device is shown to be capable of desalting an ambient electrolyte more than 90% without any external electrical power sources. Theoretical analysis for both static and transient conditions are conducted to characterize this phenomenon. These results indicate that the capillarity ion concentration polarization system can offer unique and economical approaches for a power-free water purification system.

Controllable pH Manipulations in Micro/Nanofluidic Device Using Nanoscale Electrokinetics

“…Therefore, the width of hydrogel was almost unchanged at pH = 3.5, while it expanded by 23% after 1 h in the solution of pH = 5.5 as shown in Figure 6a. When the swollen hydrogel blocked a microchannel, the configuration of microchannel was changed into micro-nano-micro-connection because the hydrogel possesses a number of nanopores inside [26,29,51]. Consequently, one can expect ICP phenomenon with the swollen hydrogel.…”

“…Since the ion depletion zone in ICP acts as an electrical filter together with zero-Reynolds number characteristics, it has been actively utilized for low abundance biomolecular separation / accumulation device [21][22][23]. If one can extract the solution from the ion depletion zone, one can use it as portable scale electro-desalination / purification [1,[24][25][26][27] device. However, shared fundamental aspects of ICP and CP have been actively studied such as vortex generation [9][10][11]28], stabilization [17,[29][30][31], mechanism of overlimiting current [12][13][14]16,18,20], phenomenon near nanopores [32][33][34][35] and concentration profile including pH variation [36][37][38], etc.…”

“…The ability to manipulate pH change provides great opportunities to integrate ICP applications with bio/chemical reaction or analysis requiring rapid pH change. For example, precise pH control is highly demanded in ICP desalination device because it produces drinking water [1,26,39]. Other crucial examples are biological applications.…”

Spontaneous diffusiophoretic separation in paper-based microfluidic device

“…Our previous work presented the spontaneous preconcentration (or selective preconcentration) method in microfluidic chip with leveraging convective flow through microchannel over diffusiophoresis induced by imbibition and ion exchange of ion exchange medium, respectively [13][14][15][16][17][18]. Especially, we had demonstrated that the velocity of the convective flow by the imbibition of the medium deviated from original Darcy's law using non-uniformly patterned ion exchange medium, but this work has the limitation of time-consuming and complex process [13].…”

Polyacrylamide-Phytic Acid-Polydopamine Conducting Porous Hydrogel for Efficient Removal of Water-Soluble Dyes

“…It is still a challenge to prepare high efficiency, reusable and broad-spectrum adsorbents. Recently, polymeric hydrogels have been considered as high performance materials for environmental applications such as desalination 30 , heavy metal ions removal 31 and radionuclides 32 due to their advantageous characteristics including adsorption-regeneration ability, economic feasibility, and environmental compatibility. However, there are few of studies on the removal of dyes using polymeric hydrogels.…”