ap9b01038_si_001.pdf (748.68 kB)
Multiple Approaches to the Buildup of Asymmetric Polyelectrolyte Multilayer Membranes for Efficient Water Purification
journal contribution
posted on 2020-01-27, 13:05 authored by Esra te Brinke, Iske Achterhuis, Dennis
M. Reurink, Joris de Grooth, Wiebe M. de VosThe versatility of
polyelectrolyte multilayer (PEM) coatings is
very promising for their use as separation layers in nanofiltration
applications. These membranes can for example be suited for the removal
of micropollutants, such as medicines and pesticides, from water.
The selectivity of PEM coatings can be further improved by so-called
asymmetric coating. In this approach, the pores of the support membrane
are filled with an open PEM layer to maintain a good water permeability,
and subsequently a thin, dense layer is coated on top to determine
the separation properties. Coating a dense top layer can be achieved
in different ways. In this work, we systematically investigate the
effectiveness of these different types of top layers. We show that
coating a top layer at lower ionic strength than the bottom layer
leads to a higher permeability and MgSO4 retention, compared
with the reference, bottom-type layer coated with the same total number
of layers. Also, other salt retentions can be improved with this approach.
However, micropollutant retentions are hardly affected. Coating a
top layer with a polyelectrolyte pair that forms denser layers at
equal ionic strength, in contrast, leads to a significant change in
separation properties with much higher MgSO4 and micropollutant
retentions and improved water permeability compared with the reference
layer. The concept of membrane optimization via asymmetric coating
is thus most effective when using different polyelectrolyte pairs
on top of each other. Moreover, we show that this approach allows
us to selectively cross-link the top layer for further enhancement
of the micropollutant retention, while water permeability is not much
reduced. Asymmetric PEM coatings are therefore a promising method
to optimize PEM membranes for micropollutant removal and other separation
processes.