Abstract
Active layers of ion separation membranes often consist of charged layers that retain ions based on electrostatic repulsion. Conventional fabrication of these layers, such as polyelectrolyte deposition, can in some cases lead to excess coating to prevent defects in the active layer. This excess deposition increases the overall membrane transport resistance. The study at hand presents a manufacturing procedure for controlled polyelectrolyte complexation in and on porous supports by support wetting control. Pre-wetting of the microfiltration membrane support, or even supports with larger pore sizes, leads to ternary phase boundaries of the support, the coating solution, and the pre-wetting agent. At these phase boundaries, polyelectrolytes can be complexated to form partially freestanding selective structures bridging the pores. This polyelectrolyte complex formation control allows the production of membranes with evenly distributed polyelectrolyte layers, providing (1) fewer coating steps needed for defect-free active layers, (2) larger support diameters that can be bridged, and (3) a precise position control of the formed polyelectrolyte multilayers. We further analyze the formed structures regarding their position, composition, and diffusion dialysis performance.
Highlights
Water scarcity and climate change drive the need for sustainable industrial processes [1]
Polyelectrolytes can be complexated to form partially freestanding selective structures bridging the pores. This polyelectrolyte complex formation control allows the production of membranes with evenly distributed polyelectrolyte layers, providing (1) fewer coating steps needed for defect-free active layers, (2) larger support diameters that can be bridged, and (3) a precise position control of the formed polyelectrolyte multilayers
We show that defect-free membranes consisting of well-known materials can be manufactured with few coating steps
Summary
Water scarcity and climate change drive the need for sustainable industrial processes [1]. To prevent pollution via produced water, often membrane filtration processes are crucial to meet purification requirements [2]. Nanofiltration is a powerful tool to purify highly polluted water by removing small organic molecules and ions. Nanofiltration membranes typically contain fixed charged groups which repel mostly polyvalent ions. Obtaining fixed charged groups in a nanofiltration membrane can be achieved with different methods, such as interfacial polymerization, or the coating of an ion-selective layer on a porous support. One prominent approach to form such layers uses polyelectrolytes that are, for instance, assembled on a microfiltration membrane [3,4]. The complexation of opposingly charged polyelectrolytes is used to form solid layers for ion removal. Various applications use different polyelectrolyte complex formation methods [5]. A layer by layer (LbL) assembly via dip coating is used to fabricate a precisely tailored polyelectrolyte coating [2,11,12,13,14]
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