Abstract
Zeolitic imidazolate framework-8 (ZIF-8) offers good hydrothermal, chemical, and thermal stabilities, and is therefore of interest in membrane synthesis. In this work, an interfacial polymerization (IP) method was applied by anchoring ZIF-8 to the skin layer of thin-film nanocomposite (TFN) membranes in order to obtain monovalent selectivity in electrodialysis. Organic trimesoyl chloride (TMC, 0.1 wt %) solutions and aqueous m-phenyl diamine (MPD, 2% w/v) solutions were used during the interfacial polymerization process. A range of polyamine (PA)/ZIF-8 based membranes was fabricated by varying the concentration of ZIF-8 in the organic solution. The properties of the primary and modified membrane were characterized by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM), water uptake, ion exchange capacity, and contact angle measurements. No significant changes of the surface structure of the PA/ZIF-8 based membranes were observed. Nevertheless, the presence of ZIF-8 under the PA layer plays a key role in the separation process. For single salt solutions that were applied in electrodialysis (ED), faster transport of Na+ and Mg2+ was obtained after introducing the ZIF-8 nanoparticles, however, the desalination efficiency remained constant. When the hybrid membranes were applied to electrodialysis for binary mixtures containing Na+ as well as Mg2+, it was demonstrated that the monovalent selectivity and Na+ flux were enhanced by a higher ZIF-8 loading.
Highlights
Population growth and economic development have resulted in global water challenges
The improved demand for water sources has posed a worldwide threat to water supply systems
Different from the previously reported strategy to form a dense cationic charged layer by chemical modification, this study presents an interfacial polymerization strategy with nanoparticles to separate monovalent and multivalent ions
Summary
Population growth and economic development have resulted in global water challenges. 50% of the world population are suffering medium water shortage, while 10% are undergoing extreme water problems [1]. It is expected that the global population would grow by nearly 40% in the forty years [2]. During the Global Risks 2015 Report of the World Economic. Water shortage had been identified as the most serious challenge for human beings in the few decades [3]. The improved demand for water sources has posed a worldwide threat to water supply systems. More than seventy percent of the Earth’s surface is covered by water, but the available freshwater only accounts for a tiny fraction of the earth’s total water supply [4].
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