Polyelectrolyte self-assembly for the next generation of membranes: From ultra-thin coatings to complete membranes

The intensification of the use and reuse of fresh water resources comes at a cost. Reports on rising levels of emerging contaminants in our water are numerous. New and better membranes are urgently needed to come to better and more sustainable water treatment processes. Over the past decade polyelectrolyte multilayers have established themselves as one of the most promising new materials in membrane Science and Technology. Novel nanofiltration membranes are prepared by the self-assembly of oppositely charged polyelectrolytes at the interfaces of a porous ultrafiltration support membrane. In this so-called Layer-by-Layer (LbL) assembly, the support membrane is alternatively exposed to polycations and polyanions, to build polyelectrolyte multilayer’s (PEMs) of controllable thickness. After coating the separation properties of the membrane are completely determined by the applied PEM layer. 
In this contribution, we will discuss how a novel approach to PEM membrane preparation can lead to membranes with unique separation properties. We present a membrane that can retain small organics at high fluxes, while allowing ions to easily pass through the membrane. The unique membrane properties also allow for new processes to more efficiently treat both surface and waste water.  
And we can even push this one step further. By a carefully controlled 1-step precipitation process, we can prepare polyelectrolyte complex based membranes, where the polyelectrolyte complex functions as the porous support membrane and as the dense separation layer. The preparation process is performed completely in water, without requiring any organic solvents. The separation performance of the new membranes is very comparable to that of the PEM based membranes that were produced using a multi-step coating method.

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