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 student’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. Visualization of the ion transport with dyes will be possible by FLIM (Fluorescence Lifetime Imaging Microscopy).  Finally, the experimental result will be validated with theoretical understanding in terms of Nernst Planck framework. 

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

Catalytically Induced Convective Flow

The electrochemical decomposition of hydrogen peroxide  has been reported to generate interfacial fluid flow by micro-pumps, and interdigitated microelectrodes[1], as well as the motion of bimetallic platinum/gold nano-motors [2]. In principle, the immersion of platinum/gold nanorods in hydrogen peroxide, triggers a series of oxidation and reduction reactions, where  is oxidized at the platinum anode into protons, electrons, and oxygen molecules, while reduction takes place at the gold cathode. The resulting ionic flux generates an electric field that is coupled with the charge density, thereby inducing an electric body force that drives interfacial fluid motion.The heterogeneous rate constant which largely influences ionic flux by way of proton generation and consumption is an important parameter that needs to be understood under steady state and transient conditions.

The kochi and Kolinger’s approach [3] will be used in determining the reaction rate constant. Several electrochemical experimental techniques such as chronoamperometry, chronopotentiometry and cyclic voltammetry, will be used in determining important parameters such as, diffusion coefficient, charge transfer, number of electrons, and peak potentials needed for evaluating the rate constant. The experimental heterogenous rate constant will be implemented in existing numerical models by way of the Damköhler’s number to ascertain its influence on the reaction flux, proton distribution, induced potential and convective flow.

For more information, contact:

Abimbola ASHAJU (a.a.ashaju@utwente.nl), Soft Matter, Fluidics and Interfaces, Meander 317)

[1]          T. R. Kline, W. F. Paxton, Y. Wang, D. Velegol, T. E. Mallouk, and A. Sen, “Catalytic micropumps: Microscopic convective fluid flow and pattern formation,” J. Am. Chem. Soc., vol. 127, no. 49, pp. 17150–17151, 2005.

[2]          T. R. Kline, W. F. Paxton, T. E. Mallouk, and A. Sen, “Catalytic Nanomotors: Remote-Controlled Autonomous Movement of Striped Metallic Nanorods**,” pp. 744–746, 2005.

[3]          R. J. Klingler and J. K. Kochi, “Electron-transfer kinetics from cyclic voltammetry. Quantitative description of electrochemical reversibility,” J. Phys. Chem., vol. 85, no. 12, pp. 1731–1741, 1981.

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, 2015, 357, 197.
[2] A. Mansourizadeh, A. J. Azad, Journal of Polymer Research, 2014, 21, 1.
[3] L. Feng, Z. Zhang, Z. Mai, Y. Ma, B. Liu, L. Jiang, D. Zhu, Angewandte Chemie International Edition, 2004, 43, 2012.
[4] X. Hou, Y. Hu, A. Grinthal, M. Khan, J. Aizenberg, Nature, 2015, 519, 70.
[5] H. Bazyar, S. Javadpour and R. G. H. Lammertink, Adv. Mater. Interfaces, 2016, 3, 1600025.[6] H. Bazyar, P. Lv, J. A. Wood, S. Porada, D. Lohse, R. G. H. Lammertink, Soft Matter, 2017, submitted.
[7] M. A. Sikkink. Superhydrophobic Non-Newtonian Slip Flow, 2017, graduation thesis.

Diffusio phoresis of photocatalytic particles

The generation of flow within the interfacial structure due to concentration gradients was described quantitatively for the first time by Anderson [1] and extended by Ajdari and Bocquet [2] for solvophobic surfaces. The flow is driven by an osmotic pressure gradient which builds up inside the interfacial layer where the interaction potential between the chemical species and solid spans (Fig. 1). Moreover, if the surface is reactive, the diffusio-osmotic flow could be promoted without any external input, through self-generated concentration gradients. If the solid surface is not immobilized, e.g in a colloidal system, the surface flow will propel small particles.

In this project, the migration of photocatalytic particles (TiO2) under self-generated concentration gradients will be studied systematically in a microreactor where an aqueous solution of an organic contaminant is contacted under continuous flow with a particle suspension containing various concentrations of the same contaminant. When UV light is turned on, the photocatalytic particles decompose the contaminant lowering the concentration inside the colloidal stream. The difference in concentration that is generated via the photocatalytic reaction leads to the migration of particles toward the higher concentration site (Fig 2).

Figure 1: Concept illustration for diffusio-osmosis

Figure 2: A methylene blue (MB) solution is contacted with a TiO2 suspension stream containing the same MB concentration in a 200 µm width channel. The dotted line is used as a guideline to show the spreading of the colloidal stream upon illumination. a. UV off b. UV on

Please do not hesitate to contact Aura Visan for additional information! (a.visan@utwente.nl)

[1] J. L. Anderson, Annu. Rev. Fluid Mech., 1989, 21, 61–99.

[2] A. Ajdari and L. Bocquet, Phys. Rev. Lett., 2006, 96, 1–4.

Ionic Diode Behaviour in Nanoporous Materials

Ionic-diodes are devices which show asymmetric transport of ions depending on the direction of the applied bias. Essentially, this means that the current in one bias (positive or negative) is very different vs. the opposite bias. This opens up the possibility for use as sensors or in desalination applications. Recently, it has been experimentally demonstrated that zeolitic imidazolate frameworks (ZIFs) can demonstrate such behaviour [1].

The mechanism for this diodic behaviour is, however, still relatively unknown. It has been postulated to be related to cation/anion size-asymmetry and shown to be influenced by pH. It is the goal of this masters work to perform detailed investigations into the charge-transport mechanism, both within the ZIF material and the surrounding fluid reservoirs, under various operating conditions. In this manner, the suitability of these materials for various desalination applications can be assessed.

The proposed masters work will involve synthesis of ZIF materials in glass (transparent) systems in order to form charge-selective interfaces. After this synthesis, detailed investigation into the ion-transport phenomena will be carried out through direct electrical characterization (conductance), along with characterization of specific ionic species transport through the use of fluorescence-sensitive dyes (fluorescence lifetime imaging microscopy) and other transport mechanisms. In this manner, the direct transport of various ionic species can be tracked throughout the system and a greater understanding behind the charge-transport mechanism obtained.

For further information, please do not hesitate to 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] Madrid et al. “Ion flow in a zeolitic imidazolate framework results in ionic diode phenomena.” Chem. Comm. 2016. 52: 2792

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