Education

Courses

The Membrane Surface Science group participates actively in the teaching of the Chemical Engineering curriculum, both in the BSc and the MSc phase. The following are the courses offered and their details:

BSc and MSc projects

Many different BSc and MSc project are possible within the MSuS group. Projects can involve making or coating membranes (Material Science), but can also be more focused on characterizing membranes and optimizing their performance for a specific application (Process Technology). For a most up-to-date overview of possible projects please contact w.m.devos@utwente.nl.

Some examples of possible projects are given below:


1. Membranes by Aqueous Phase Separation

Elif Nur Durmaz (1), Wouter Nielen(1), Joshua Willott  (1), Wiebe de Vos(1)

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

Project Outline

Membranes are used in a variety of processes including the production of clean drinking water, artificial kidneys, CO2 capture, and food processing. Due to their large application areas and many advantages of membranes over other separation technologies, the membrane market is continuously growing. However, a major concern regarding membrane production is the use of large quantities of aprotic organic solvents such as N-Methyl-2-pyrrolidone. Such solvents are harmful to humans and the environment. This project is focused on investigating a novel, environmentally friendly technique for the production of membranes without using organic solvents. Here, membrane formation relies on the phase separation of polyelectrolytes either through a pH switch or a complexation with an oppositely charged polyelectrolyte. The main aim is to understand which factors govern the morphology and separation performance of the membranes. Additionally, improving mechanical and chemical stability with cross-linking will be investigated.

     

Figure 1 - Porous symmetric and porous asymmetric structure of membranes obtained by tuning conditions of the aqueous phase separation

Project Description

Polyelectrolytes are polymers that contain repeating charged groups. Due to these charges, they are soluble in polar solvents like water. Polyelectrolytes can be separated into two categories based on the charged groups. 1. Weak: when their charge depends on the pH of the medium or 2. Strong: when the charge is independent of pH. Weak polyelectrolytes can be used to precipitate a hydrophobic polyelectrolyte from water by shifting to a pH where the polyelectrolyte is uncharged.  Alternatively, this can also be used to charge an uncharged hydrophilic weak polyelectrolyte. When this is mixed with an oppositely charged strong polyelectrolyte, they form a complex, which can be solid. In both cases, a phase separation occurs and under the right conditions, this can be used to form a porous, asymmetric membrane. By controlling the rate at which the polyelectrolyte is charged or uncharged the kinetics of the phase separation can be controlled which in turn gives control over the structure of the precipitate that is formed. This allows us to fabricate membranes with controllable properties. To fine-tune membrane performance e.g. membrane flux or retention, additives can be used. Additionally, the mechanical and chemical stability can be significantly improved with cross-linking. To assess the membrane performance several filtration techniques are used. In addition, the morphology is imaged using scanning electron microscopy. The membrane can then be optimized towards specific applications, such as gas-separation, ion removal or the treatment of oily wastewater.

Project Outcome

This project is expected to lead to a new and sustainable approach to produce membranes. Moreover, the newly produced membranes are expected to have unique separation properties relevant to a number of applications.

2. Polyelectrolytes for an improved aquaporin embedded top layer for next generation forward osmosis membranes

Dennis Reurink(1), Wiebe M. de Vos (1)

(1)Membrane Surface Science (MSuS)

Introduction

An emerging separation and desalination technology that shows great potential is forward osmosis (FO). FO uses osmotic pressure gradients to transport water across a semipermeable membrane. These membranes are usually based on reverse osmosis (RO) membranes, which lack, however, suitability for FO applications [1]. A way to create new membranes truly optimized for FO, is by incorporating aquaporin containing vesicles (AQPVs) in the separating layer [2]. These vesicles have the aquaporin protein incorporating in the vesicle wall as shown in Figure 1. This aquaporin protein acts as a water channel that allows solely water and block all other solutes [3]. In this way the permeation and rejection properties are enhanced.

Another versatile technique is the self-assembly of oppositely charged polyelectrolytes (PEs) on the surface of a porous support membrane. In this so-called Layer-by-Layer (LbL) assembly, the support membrane is alternatively exposed to polycations and polyanions [4]. Such a PEM coating is easily applied on all geometries. In this study, the focus will be on making a PEM coating with the incorporation of AQPVs. Since the interaction between the vesicles and the multilayer is important, the distribution of the AQPVs is first studied. Subsequently, a layer will be produced and tested on its FO and RO performance.

Study

In order to create a more permeable and selective layer, aquaporin containing vesicles (AQPVs) can be used. These vesicles are incorporated in the separating layer of the membrane.

In order to control the distribution of the aquaporin vesicle, various polyelectrolytes can be used which have different interaction with the AQPVs. Also different coating environments, like salt concentration, pH, and solvent can be used to control the distribution of the vesicles.

In this MSc project, the distribution of the AQPVs will be studied on model surfaces. When the distribution is controlled and understood a separating layer will be made and incorporated on a membrane.

Methods

PEMs can be made by dip-coating silicon wafers or membranes in a solution containing a certain polyelectrolyte. AQPVs can be also be coated by means of dip-coating.

The distribution of AQPVs can be seen with a high resolution scanning electron microscope. Adsorption of both the PEs and AQPVs are measured with reflectometry and further characterization can be done with ellipsometry, zeta potential, and contact angle measurements. The knowledge obtained from model surfaces (silicon wafers) will be translated into hollow fiber membranes. The membranes will be coated under the same conditions as the model surfaces and will be tested on their performances in forward and reverse osmosis operating conditions.

Figure 1: The water-selective aquaporin protein incorporated in the vesicle wall.

References

1. Shaffer, D.L., et al., Forward osmosis: Where are we now?, Desalination, 2015. 356.

2. Tang, C., et al., Biomimetic aquaporin membranes coming of age, Desalination, 2015. 368.

3. Murata, K., et al., Structural determinants of water permeation through aquaporin-1, Nature, 2000. 407(6804).

4. Decher, G., Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites, Science, 1997. 277(5330).

3. Polyelectrolytes for new generation reverse osmosis hollow fiber membranes

Dennis Reurink (1), Wiebe M. de Vos (1)

(1)Membrane Surface Science (MSuS)

Introduction

Nowadays most membranes for nanofiltration (NF) and reverse osmosis (RO) are based on thin film composite (TFC) membranes. On a TFC membrane, a thin film is coated on a porous support with interfacial polymerization. A major disadvantage is that defect free hollow fiber membranes based on the TFC principle is merely impossible [1]. A new versatile technique for membrane the self-assembly of oppositely charged polyelectrolytes (PEs) on the surface 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 [2]. Such a polyelectrolyte multilayer (PEM) coating is easily applied on all geometries. In this study, the focus will be to create a PEM based membrane suitable for RO applications. In order to achieve RO performance, PEMs should be made as dense as possible by means of crosslinking and the use of different kinds of PEs. Subsequently, the layer will be characterized and tested on its RO performance.

Study

Creating more intrinsic bonds will increase the rejection properties of an active membrane layer. Crosslinking is a manner to create more intrinsic bonds and can easily be done by heat or a catalyst. Many moieties of PEs are amines or carboxylic acids which can easily be crosslinked, as shown in Figure 1.

Crosslinking of PEMs has already shown to be a promising way to create an active layer capable of retaining salts [3]. For FO purposes, the layer has to be as dense as possible in order to cope with highly concentrated saline streams. In order to control the layer density, different materials can be used that influence the intermolecular distance.

In this MSc project, different types of crosslinking techniques and materials will be evaluated. Materials will vary from aliphatic, branched, to aromatic structures while controlling and monitoring the performance of the membrane. 

Methods

PEMs can be made by dip-coating silicon wafers or membranes in a solution containing a certain polyelectrolyte. The growth and properties of these multilayers can be monitored by using techniques like reflectometry, ellipsometry, contact angle, and zeta potential measurements. 

Crosslinking can be done catalyzed or non-catalyzed. Non-catalyzed reactions take place under the influence of heat. To see if crosslinking has taken place, the layer will be characterized by, e.g., FTIR measurements.

The knowledge obtained from model surfaces (silicon wafers) will be translated into hollow fiber membranes. The membranes will be coated and crosslinked under the same conditions as the model surfaces and will be tested on their performances in forward osmosis operating conditions.

Figure 1: Crosslinking of polyelectrolyte multilayers [4].

References

1. Lau, W.J., et al., A recent progress in thin film composite membrane: A review, Desalination, 2012. 287.

2. Decher, G., Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites, Science, 1997. 277(5330).

3.  Park, J., et al., Desalination membranes from pH-controlled and thermally-crosslinked layer-by-layer assembled multilayers, Journal of Materials Chemistry, 2010. 20(11).

4.  Sullivan, D.M. and M.L. Bruening, Ultrathin, cross-linked polyimide pervaporation membranes prepared from polyelectrolyte multilayers, Journal of Membrane Science, 2005. 248(1-2).

4. Exploration of suitable membrane structures for green-energy water purification

Mehrdad Mohammadifakhr (1)

(1) Advanced Membranes for Aqueous Applications (AMAA)

Project Outline and description

In this project, we have a close cooperation with a membrane company in Denmark (Aquaporin A/S) to fabricate forward osmosis (FO) membranes. Membrane technology is the most applied method for water purification. Recently increasing attention is being paid to the FO technology. FO technology is a green technique which can solve unique challenges where other techniques such as RO, NF and UF struggle [1]. Fabrication of biomimetic membranes based on aquaporins has attracted a lot of attention in recent years. Aquaporins are cell proteins which act as small water channels to allow fast transport of only water molecules, meanwhile blocking all other types of molecules [2]. FO membranes consist of a thin, selective separating layer on top of a porous support. Both layers are important for the properties of the membrane such as its water flux, reverse salt flux, and salt rejection. So far, RO-type supports have been mostly used for FO membranes which however result in high internal concentration polarization (ICP) and low water flux due to their dense and thick layer. These pressure resistant supports are unnecessary due to the low pressure applied in FO. Therefore, it seems essential to fabricate an ideal and custom-made support for FO. However, there is an uncertainty about the suitable support structure in literature. Some claim that a finger-like is the best structure while in others sponge-like structures are assumed as the most suitable [Figure 1].

The degree of ICP is determined by its S-factor (eq.1), in which A (water permeation) and B (salt permeation) are measured in a low-pressure RO experiment, including the water flux (Jw) as determined in an FO experiment. In order to measure the S-factor, application of the active layer is pre-requisite. The application of the active layer is performed by so-called interfacial polymerization technique.

Hollow fibers are the best choice for FO supports because of high control on their structure in the fabrication step. Hollow fiber supports are fabricated using a solution containing base-polymer (dissolved in solvent) (dope solution) and a solution of non-solvent (bore solution). These two solutions are used in a spinning machine where they get in contact with each to form the hollow fiber.

Trying different polymers as base-polymer and changing the polymer-to-solvent ratio would lead to different recipes where different morphologies can be obtained (finger-like and sponge-like structures), while the surface properties remain the same. After application of an active layer, these membranes will be tested for their FO performance to obtain the S-factor. Finding the most suitable morphology for FO membranes is the outcome of this project.

For more information, please contact:

Mehrdad Mohammadifakhr (m.mohammadifakhr@utwente.nl): Advanced Membranes for Aqueous Applications (AMAA), Meander 323

References:

[1] Tzahi Y. Cath, Amy E. Childress, Menachem Elimelech; Forward osmosis: Principles, applications, and recent developments; Journal of Membrane Science 281 (2006) 70–87

[2] Lingling Xia, Mads Friis Andersen, Claus Hélix-Nielsen, and Jeffrey R. McCutcheon; Novel Commercial Aquaporin Flat-Sheet Membrane for Forward Osmosis; Ind. Eng. Chem. Res. 2017, 56, 11919-11925

5. Simultaneous coating during hollow fiber support fabrication- an attempt for fast fabrication

Mehrdad Mohammadifakhr (1)

(1) Advanced Membranes for Aqueous Applications (AMAA)

Project Outline and description

In this project, we are cooperating with a membrane company in Denmark (Aquaporin A/S) to fabricate forward osmosis (FO) membranes. Membrane technology is an often-applied method for water purification. Increasing attention is being paid to the FO technology. FO technology is a less energy consuming technique which can solve unique challenges where other techniques such as RO, NF and UF struggle. FO membranes consist of a thin, selective separating layer on top of a porous support. Both layers are important for the properties of the membrane such as its water flux, reverse salt flux, and salt rejection. The FO supports are fabricated by phase inversion technique and subsequently, an active layer is coated on their surface [1]. Hollow fibers (HF) are the best choice for FO supports because of the excellent control of their structure in the fabrication step and their high surface area. HF supports are being fabricated using a solvent containing a base-polymer (dope) and a non-solvent (bore). These two are brought in contact with each in a spinning machine to form the hollow fiber. These HF supports are then post-treated by either interfacial polymerization (IP) technique or layer-by-layer (LbL) technique to apply the active layer.

Interfacial polymerization (IP) is a reaction between two highly reactive monomers that are dissolved in two immiscible liquids (one dissolved in an aqueous and the other in an organic phase) [Figure 1] [2].

In the Layer-by-Layer (LbL) technique, the film is formed by physically binding alternating layers of oppositely charged materials (polyelectrolytes) with wash steps in between [Figure 2] [3].

So far, the active layers formed by the LbL technique haven’t shown the high salt rejection which is necessary for FO membranes. On the other hand, the IP coated supports showed better results in terms of better FO performance (high salt rejection and high water flux). However, IP coating has its own disadvantages of being a laborious and in some cases, irreproducible technique.

Therefore, a new coating procedure which reduces the coating defects as much as possible seems essential. Alternatively, instead of coating the membrane after support fabrication, the coating reaction can be included in the phase inversion process itself by adding one monomer/polyelectrolyte in the dope solution and the other monomer/polyelectrolyte in the bore solution. This simultaneous coating is going to be tested in this assignment which should lead to a more uniform and suitable active layer for FO.

Several experiments are expected to be carried out in this assignment such as hollow fiber fabrication, pure water permeability, pore size measurements, SEM analysis, FO performance, and low-pressure RO.

For more information, please contact:

Mehrdad Mohammadifakhr (m.mohammadifakhr@utwente.nl): Advanced Membranes for Aqueous Applications (AMAA), Meander 323

References:

[1] Tzahi Y. Cath, Amy E. Childress, Menachem Elimelech; Forward osmosis: Principles, applications, and recent developments; Journal of Membrane Science 281 (2006) 70–87

[2] Michiel J.T. Raaijmakers, Nieck E. Benes; Current trends in interfacial polymerization chemistry; Progress in Polymer Science 63 (2016) 86–142[3] Joseph J. Richardson, Mattias Björnmalm, Frank Caruso; Technology-driven layer-by-layer assembly of nanofilms; Science 348 (6233), aaa2491