Abstract
Nanofiltration (NF) membrane typically prepared by interfacial polymerization (IP) technology is facing the problems of low permeance and flux-selectivity trade-off effect, which will seriously affect the efficiency of water purification. Here, novel NF membranes with a thin and crumpled polyamide (PA) layer were obtained by introducing low concentration of soluble inorganic salts (≤2 wt%) in the IP process and thermally induced crystallization of inorganic salts in the heat treatment process. The forces generated by the growth of inorganic salt crystals inevitably stretched the nascent and flexible PA layer, and further the inorganic salt crystals can sacrifice themselves in water, contributing to the formation of a thin and rough PA layer with crumpled nanostructure. Using NaCl as an example, the resulting NF membrane exhibited the permeation flux as high as 84 L/m2 h at 4 bar while maintaining a high rejection of 96.2% for Na2SO4. Meanwhile, it is universal for other soluble inorganic salts such as KCl, Na2SO4, KNO3 and CaCl2 to improve the filtration performance of NF membrane. This study is the first to combine the growth of inorganic salt crystals with the morphology regulation of PA active layer in the heat treatment process, which will further expand the research method of NF membrane with efficient water purification.
| Original language | English |
|---|---|
| Article number | 118645 |
| Journal | Journal of Membrane Science |
| Volume | 617 |
| DOIs | |
| State | Published - Jan 1 2021 |
| Externally published | Yes |
Funding
The work was financially supported by the Opening Project of Jiangxi Province Key Laboratory of Polymer Micro/Nano Manufacturing and Devices ( PMND201904 ), and the Doctoral Scientific Research Starting Foundation of East China University of Technology ( DHBK2019115 , DHBK2019116 ). Faced with the global crisis of serious shortage of potable water, the development of water purification and desalination based on membrane technology has become a prevailing trend [ 1?3]. Among various pressure-driven membranes, nanofiltration (NF) membrane has been widely used in many separation processes such as dye removal [4], seawater desalination [5], wastewater treatment [6], and pharmaceutical purification [7] due to its high efficiency and low energy consumption in removing multi-valent ions and organic small molecules with cut-off molecular weight greater than 200 Da [8,9]. Advances in technology and materials have facilitated the emergence of a variety of methods for preparing NF membranes such as coating [10], self-assembly [11], interfacial polymerization (IP) [3,5], 3D printing [12], chemical vapor deposition [13], and vacuum filtration [14], in which IP has been most commonly used owing to its operation simplicity and technical maturity. Generally, IP deposits a polyamide (PA) active layer on top of a porous support layer through the diffusion and rapid reaction of water phase monomer to oil phase monomer [15,16]. However, highly crosslinked polymer chains tend to form dense PA layers which are not conducive to the transport of water molecules [17]. The disadvantages of low permeance and flux-selectivity trade-off obviously reduce water production rate and enhance the production cost, restricting their application in NF process. Therefore, it is urgent to find novel experimental methods or materials based on IP technology for improving the permeance while maintaining a high-solute rejection rate.The work was financially supported by the Opening Project of Jiangxi Province Key Laboratory of Polymer Micro/Nano Manufacturing and Devices (PMND201904), and the Doctoral Scientific Research Starting Foundation of East China University of Technology (DHBK2019115, DHBK2019116).
Keywords
- Morphology regulation
- Nanofiltration (NF) membrane
- Soluble inorganic salts
- Thermally induced crystallization