Education

Keywords: Polyelectrolyte multilayer membranes, nanofiltration, micropollutants, layer-by-layer

Global water quality and safety is under threat by the rising concentrations of organic micropollutants (OMPs) in surface and drinking water. OMPs are small organic molecules that originate from agricultural, pharmaceutical and industrial sources, with potential long term harm towards humans, aquatic life and the environment. Currently, reverse osmosis and tight nanofiltration (NF) membranes have proven to be promising solutions for removal of OMPs, however they have significant limitations such as low water permeability, high operating pressures, high salt retentions and the requirement for remineralization of the permeate to restore mineral quality for drinking water applications.

In the recent years, polyelectrolyte multilayer (PEM) based nanofiltration membranes have been applied as an emerging solution. PEM membranes are constructed by alternatively coating polycations and polyanions on an ultrafiltration support using the Layer-by-Layer technique (LbL). The LbL method allows for precise control over membrane performance, by tuning the pore size, surface charge, permeability and selectivity [1]. Current research shows that PEM membranes with high OMPs and high permeabilities have been successfully fabricated by building asymmetric membrane systems, where pores are first closed off with a more open coating to achieve high permeabilities, followed by a thin dense coating on top to stop OMPs and achieve low molecular weight cut-offs (MWCO) [2]. A schematic representation is given in figure 1 [3].

A major drawback of these systems is the high salt retentions towards trivalent and divalent ions. As a result, concentrated brine streams are created that are difficult to treat. Furthermore additional remineralization steps are necessary for permeate streams for drinking water applications.

In this project, you will be working on towards PEM NF membranes that are selective towards OMPs, while maintaining high salt permeability. During this project, you will:

· Review existing literature on PEM membranes, analyze existing multilayers systems and study the coating parameters for these systems, such as the pH, ionic strength, types of PE’s.

· Come up with new experimental designs, with new coating conditions and parameters to achieve the goal of high OMP removal and low salt retentions.

· Learn how to coat PEM membranes by the LbL approach using the dip coating robot.

· Analyze the performance of fabricated membranes by doing retention measurements, reflectometry analysis, ellipsometry analysis and MWCO experiments.

· Learn and run the in-house cross-flow pilot setup to carry out experiments.

This project is part of the ERC Mosaic project. For further information, please contact: h.zengin@utwente.nl

References

[1] W. A. Jonkers, E. R. Cornelissen, and W. M. de Vos, “Hollow fiber nanofiltration: From lab-scale research to full-scale applications,” Mar. 05, 2023, Elsevier B.V. doi: 10.1016/j.memsci.2022.121234.

[2] M. A. Junker, W. M. de Vos, J. de Grooth, and R. G. H. Lammertink, “Relating uncharged solute retention of polyelectrolyte multilayer nanofiltration membranes to effective structural properties,” J Memb Sci, vol. 668, Feb. 2023, doi: 10.1016/j.memsci.2022.121164.

[3] E. te Brinke, I. Achterhuis, D. M. Reurink, J. de Grooth, and W. M. de Vos, “Multiple Approaches to the Buildup of Asymmetric Polyelectrolyte Multilayer Membranes for Efficient Water Purification,” ACS Appl Polym Mater, vol. 2, no. 2, pp. 715–724, Feb. 2020, doi: 10.1021/acsapm.9b01038.

Organic micropollutant (OMP) contamination in water, such as pharmaceuticals, pesticides, and personal care products, is an emerging concern for global water treatment efforts. Although present in trace amounts, these OMPs can be harmful even at very low concentrations. Due to their small molecular sizes, many existing filtration technologies struggle to remove them from water sources effectively. As water scarcity intensifies due to population growth, industrial activities, and climate change, the need for advanced filtration technologies becomes crucial.

Polyelectrolyte Multilayer (PEM) membranes, constructed by alternating layers of positively and negatively charged polyelectrolytes, exhibit unique properties such as tunable pore size, surface charge, and permeability. Current PEM membranes are either highly selective for OMPs or exhibit strong stability, but achieving both simultaneously remains a challenge. This project aims to develop membranes that balance high selectivity and stability to improve overall performance. This project aims to develop dense and stable PEM-based nanofiltration (NF) membranes for surface water treatment by testing novel polyelectrolyte pairs. Additionally, the membranes will be evaluated for their stability and performance in harsh conditions, ensuring they maintain their selectivity and efficacy against micropollutants even after repeated use, leveraging their advanced properties to improve water purification efficiency.

Keywords: Polyelectrolyte multilayers, nanofiltration, dense membranes

During this project, you will focus on:

·        Conducting an in-depth review of current literature on PEM membranes, focusing on their working mechanisms, properties, and efficacy in water treatment applications. This review will cover key topics such as the properties of different polyelectrolytes, their ion selectivity behavior, and the latest innovations in PEM membrane technology.

·        Fabricate PEM membranes using the layer-by-layer technique, focusing on dense membrane formation to enhance treatment efficiency.

·        Performing experiments to evaluate the permeability, salt retention, MP retention, and molecular weight cut-off (MWCO) of PEM membranes.

·        Explore symmetric and asymmetric coating configurations for optimized membrane performance.

·        Comparing the performance of dense PEM membranes with conventional NF membranes, focusing on improvements in selectivity.

This project is ideal for master's students seeking hands-on experience in advanced water treatment technologies.

For more information, please contact: Sina Rezaei (Sina.rezaei@utwente.nl)

Esra te Brinke ⁽¹⁾, Wiebe de Vos ⁽¹⁾

⁽¹⁾Membrane Surface Science (MSuS), Membrane Science and Technology Cluster

e.tebrinke@utwente.nl

Project background

Polyelectrolyte multilayer (PEM) membranes, formed by alternate adsorption of polycation and polyanion nanolayers on a membrane support, are recently becoming more and more important in membrane applications. One intrinsic feature of PEM membranes is that they have different properties depending on the terminating layer, the so-called odd-even effect. Not only the polarity of the membrane surface is determined by the terminating layer, but typically also the total charge density and therefore the swelling of the layer [1]. Therefore, besides ion retention also water permeability of the membrane is influenced by this odd-even effect, as well as the molecular weight cut-off of neutral molecules. This effect is very well visible as a zig-zag pattern in membrane permeability as a function of the number of coated polyelectrolyte layers (figure 1). During a recent project we have observed that the odd-even effect of poly(allylamine hydrochloride) and poly(acrylic acid) can switch depending on coating pH, i.e. that the coating pH can determine which of the two polyelectrolytes will induce most swelling as the terminating layer. However, both at low and high pH the odd-even effect was exactly opposite to what we expected, so apparently our theoretical framework is not complete. For a better fundamental understanding of PEM membrane production and properties, we want to further investigate this.

Figure 1. Odd-even effect on the water permeability when alternatingly coating poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) layers [1].

Project description

The aim of this student project is to study an additional pH-sensitive polyelectrolyte pair and see if we can obtain similar results or not. Permeability and molecular weight cut-off will be determined by crossflow experiments and GPC. Additionally, we want to take a more fundamental look how pH affects the odd-even effect. PEM build-up will therefore be studied by reflectometry and ellipsometry. Hydrophobicity could be tested by contact angle measurements. Depending on the duration of the project, some of the experiments from the previous work might be repeated or additional measurements on that PEM system might be performed. Finally, we will try to relate fundamental insights into the performance of polyelectrolyte multilayer membranes produced with different terminating layers and coated under different pH conditions.

References

[1] J. de Grooth; A tale of two charges: Zwitterionic Polyelectrolyte Multilayer Membranes; doctoral thesis, Ipskamp printing Enschede, 2015