Desalination by Electrodialysis Using a Stack of Patterned Ion‐Selective Hydrogels on a Microfluidic Device

Abstract

This study reports a novel approach for separation of charged species using anion‐exchange hydrogel (AEH) and cation‐exchange hydrogel (CEH) in a microfluidic device. The capillary line pinning technique, which is applied in this study, enables in situ fabrication of alternating AEH and CEH that are placed in confined compartments. Adjacent enriched and depleted streams are obtained in continuous flow when a potential difference is applied over the hydrogel stack. The desalination performance of the microchip is demonstrated at different salt concentrations (0.01 × 10−3–1× 10−3m sodium chloride), potentials (10–100 V), current densities (12–28 A m−2), and liquid flow rates (0–5 µL min−1). It is shown that the microchip is able to remove ≈75% of the salt initially present in the depleted outlet streams at inlet stream concentrations of 1 × 10−3m sodium chloride. Besides desalination, the microchip allows study of ion transport in the ion‐selective hydrogels to elucidate the interplay of transport phenomena at the electrolyte–hydrogel interface during the desalination process.

Cellular Structured CNTs@SiO2 Nanofibrous Aerogels with Vertically Aligned Vessels for Salt‐Resistant Solar Desalination

“…Compared with other water treatment technologies, such as nanofiltration, reverse osmosis, electrodialysis, the solar evaporation technology using CNFAs is efficient, low cost, energy-saving, and convenient maintenance which makes it unparalleled advantages and potential for seawater desalination and wastewater treatment. [48][49][50][51][52][53] In summary, we assemble SiO 2 nanofibers and CNTs into cellular structured nanofibrous aerogels with vertically aligned vessels and porous vessel walls by the fiber freeze-shaping technology. With this unique cellular architecture, the CNFAs exhibit an excellent salt-resistance with stable and efficient solar desalination even in 20% brine and under 6-sun irradiation, better than current reports.…”

Enhanced ion transport using geometrically structured charge selective interfaces

“…Characterization of the hydrogels and their swelling behavior in microchip was reported earlier. 26 As the cross-linking reaction is inhibited by oxygen, patterning and polymerization processes were performed in a nitrogen environment. Hydrogel precursors were degassed in a vacuum chamber set at 7 kPa for 15 minutes and used immediately after degassing.…”

“…Redistribution of charges inside the hydrogels as a result of an applied potential was considered in the previous work, but no significant deviations from the expected hydrogel behavior were found and therefore the possible influence of this was neglected in the analysis in this work. 26 All microchips consist of six parallel microchannels connected through alternating AEH and CEH, as depicted in Fig. 1b.…”

“…[17][18][19][20][21][22][23][24][25] We have previously reported a microfluidic platform using charge selective hydrogels for the microscopic investigation of ion transport in electrodialysis systems. 26 Hydrogels are versatile materials that can easily be patterned with different geometries on the micro-scale. Therefore, hydrogels can be used to build micro-electrodialysis systems for rapid investigation of the influence of geometry on ion transport which can be applied in large scale electrodialysis systems.…”

“…This allows us to microscopically observe concentration profiles and depletion zones adjacent to the hydrogel compartments. The previous work 26 was a proof of principle of using patterned and charged hydrogels for microfluidic investigation of ion transport phenomena in electrodialysis. In this work, we investigate the influence of hydrogel geometry on the development of ion depletion zones and the current-voltage characteristics.…”