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Ion transport through graphene

Graphene is increasingly studied as a potential material for membrane applications. It does not have any separation capability in its pristine state, however a perforated monolayer graphene membrane can selectively separate material due to steric or electrostatic exclusion [1, 2].  In our work, we use ion-bombarded perforated monolayer graphene membrane supported on a polymer foil to study diffusional ion transport properties through graphene [3]. This membrane allows positive ions to pass through and blocks negative ions, acting as a cation-exchange membrane (CEM). We have studied the selectivity of the membrane with varying concentrations from range where Donnan potential dominates to concentrations where the diffusion potential dominates and the membrane loses all its selectivity. We have also analyzed our experimental results with theory, based on Donnan equilibrium and the Teorell, Mayer and Sievers (TMS) theory.  

 

So far, we have done our measurements without applying any electric field across the membrane and the observations are based on diffusional ion transport. Now, we need to explore how the ions transport through the membrane when an electric field is applied across the membrane. The aim of the current master’s project is to study the ion transport behaviour of the graphene membrane with the application of electric field. Also, in the later part of the project the ion transport will be studied with varying number of pores in the membrane. Finally, the experimental result will be validated with theoretical understanding.  

For more information, feel free to contact Madakranta (Dona) Ghosh:
m.ghosh@utwente.nl

[1] O’Hern et al. “Selective Ionic Transport through Tunable Subnanometer Pores in Single-Layer Graphene Membranes.” Nano Lett. 2014, 1234-1241

[2] Rollings et al. “Ion selectivity of graphene nanopores” Nature Comm., 2016, 7, 11408

[3] Madauß et al. “Fabrication of nanoporous graphene/polymer composite membranes” Nanoscale, 2017, 9, 10487

Theoretical Investigation of Electroforming MOFs on Copper Hollow Fibers

Recently in the Films in Fluids group a novel technique for producing highly controllable hollow fibres using an environmentally friendly ionic-gelation technique has been developed. Through the addition of nanoparticles, metallic oxide or metallic hollow fibres can be easily fabricated. Using this technique, the FiF group has pursued the intriguing idea of utilizing this simple fibre production technique in order to fabricate copper-based metal organic frameworks (MOFs). MOFs are metal-ions which are coordinated to organic ligands, forming network structures (1d, 2d or 3d) that can be porous. MOFs are of potential interest in catalysis, sensing and gas separation and having the capacity to form high specific surface area hollow fibres is an attractive option for making use of the unique MOF properties.

Research has been carried out in fabricating Cu(BTC) using an electrochemical synthesis method. In this approach, a Cu hollow-fibre is used as the working electrode in a cell containing an ethanol-water mixture containing an organic ligand - trimesic acid (BTC). BTC then reacts with copper to form Cu-BTC, a copper-hollow fibre MOF. The underlying mechanism behind this transformation and its enhancement using applied potential has been postulated but not confirmed.

It is the goal of this proposed Masters assignment to develop a theoretical model to understand this system, which we are presently investigating experimentally. This model framework can then be implemented in a 2 or 3d numerical simulation (COMSOL) in order to predict or fit experimental results. For example, what is the role of the electric-field distribution within the system, ion dissociation in the water-ethanol mixture, etc. This will greatly aid in understanding of the potential of this approach for synthesis of MOF hollow-fibres and its potential applicability at larger scales.

For more information, please contact:

Özlem Haval Demirel (o.h.demirel@utwente.nl), Films in Fluids, Meander 322

Jeff Wood (j.a.wood@utwente.nl), Soft Matter, Fluidics and Interfaces, Meander 313

[1] Schäfer et al. Unraveling a two-step oxidation mechanism in electrochemical Cu-MOF synthesis. Chem. Comm. 2016. 52: 4722

MSc Assignment: Simultaneous coating during hollow fiber support fabrication- an attempt for fast fabrication

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 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

Reference:

[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

slippery liquid infused membranes (SLIMs)

The rapid industrial growth in the field of oil and gas and petrochemical has lead to the production of large amount of oily waste water. Due to the environmental issues, the necessity to treat oily waste water is an inevitable challenge. Polymeric membranes have shown to be a good candidate for oily waste water treatment mainly due to their facile fabrication procedures. However, the main disadvantage of application of polymeric membranes is fouling [1]. To improve the anti-fouling properties of membranes, different strategies have been examined as follows [2,3]:
-       Physical/chemical surface modification
-       Blending with hydrophilic additives
-       Superhydrophobic/superolephilic membranes

In this project, application of a new type of membrane, called, slippery liquid-infused membrane (SLIM) for treating oily waste water will be investigated. The concept of SLIM is inspired by slippery liquid-infused porous surfaces (SLIPS) which have shown anti-biofouling properties and multi-phase transport capability without clogging [4]. The liquid-filled pore will be opened in response to the system pressure. Therefore, a liquid-lined path is made for passage of the transport fluid. Once the pressurizing is stopped, the infusion liquid (fluorinated oil) can be re-infused back and closed status of the pore can be recovered. This is called gating mechanism which is schematically shown in figure 1 [5].


Figure 1. Schematic of gating mechanism in SLIM and comparison of a dry pore (a) to liquid-filled pore (b).

The presence of the thin liquid layer on the pore wall is essential for anti-fouling properties of SLIMs. So far, the retention of the infusion liquid has been tested by pushing pure water as well as different types of surfactant solutions (anionic, cationic, non-ionic and zwitterionic) through SLIM. As schematically shown in figure 2, displacement of the infusion liquid by water (immiscible displacement) has lead to the preferential flow path ways for water transport through the membrane. The displacement mechanism corresponds to capillary fingering invasion regime which was confirmed by microfluidic experiments using a chip mimicking porous membrane (figure3) [6].


Figure 2. Immiscible displacement in SLIM showing preferential flow path ways for water transport.


Figure 3. Liquid-liquid displacement in the microfluidic chip. The chip is infused with oil (yellow phase) and water is pushed at flow rate of 0.2 ml/s from the right side (blue phase).

In order to better investigate the effect of surfactants on retention of the infusion liquid on the pore wall, new type of microfluidic experiments have been planned [7]. Particle image velocimetry (PIV) will be used to investigate the velocity profiles and better understand Maragoni type stresses on the liquid-lined wall.

For more information, please contact Hanieh Bazyar: h.bazyar@utwente.nl

[1] M. Padaki, R. Surya Murali, M. S. Abdullah, M. Misdan, A. Moslehyani, M. A. Kassim, N. Hilal, A. F. Ismail, Desalination, 2015357, 197.
[2] A. Mansourizadeh, A. J. Azad, Journal of Polymer Research201421, 1.
[3] L. Feng, Z. Zhang, Z. Mai, Y. Ma, B. Liu, L. Jiang, D. Zhu, Angewandte Chemie International Edition, 200443, 2012.
[4] X. Hou, Y. Hu, A. Grinthal, M. Khan, J. Aizenberg, Nature, 2015519, 70.
[5] H. Bazyar, S. Javadpour and R. G. H. Lammertink, Adv. Mater. Interfaces20163, 1600025.[6] H. Bazyar, P. Lv, J. A. Wood, S. Porada, D. Lohse, R. G. H. Lammertink, Soft Matter2017, submitted.
[7] M. A. Sikkink. Superhydrophobic Non-Newtonian Slip Flow, 2017, graduation thesis.

MSc Assignment: Exploration of suitable membrane structures for green-energy water purification

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 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

Reference:

[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

BSc or MSc Assignment: Further improvement of the FO membrane active layer in order to achieve a higher salt rejection

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 which is assumed to be a green-energy technique. 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 [1]. Hollow fibers (HF) are the best choice for FO supports because of high control on their structure in the fabrication step and their high surface area. The supports are initially fabricated by phase inversion technique and subsequently, an active layer is coated on their surface. Alternatively, instead of coating the membrane after support fabrication, the coating reaction can be included in the phase inversion process (simultaneous coating).

Recently, we managed to simultaneously coat the HFs during their fabrication by using two polyelectrolytes as active layer formers [Figure 1]. These HF membranes showed 45% NaCl rejection at 2 bars. However, the rejection should be further increased (>60%) to achieve a better FO performance. This improvement can be realized by post-treating the HF membranes by techniques such as: interfacial polymerization (IP coating) [2], layer-by-layer assembly (LBL coating) or chemically/thermally crosslinking [3]. These three different post-treatments will be tested in this assignment.

For more information, please contact:

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

Reference:

[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] Hongxia Guo, Mengmeng Chen, Qiang Liu, Ziming Wang, Suping Cui, Guojun Zhang; LbL assembly of sulfonated cyclohexanone–formaldehyde condensation polymer and poly(ethyleneimine) towards rejection of both cationic ions and dyes; Desalination 365 (2015) 108–116