Research

Research Themes

Mechanism of salt rejection in desalination membranes

(Noga Fridman-Bishop, Vesselin Kolev)

In desalination membranes the salts are separated from water in a very thin (10-200 nm) selective layer made of polyamide, however, how that happens and how different ions are separated is still not well understood. We develop models and methods to study  salt transport in RO and NF and study the mechanism of using various experimental techniques, in particular, electrochemical impedance spectroscopy (EIS). We also use atomistic molecular dynamics (MD) simulations  to gain better understanding of molecular mechanisms involved in salt and water transport.

sea water composition

Given sea water composition, what will be the composition of permeate and retentate?

Principle of EISPrinciple of EIS:  membrane conductivity supplies unique signatures of transport mechanism.

polymer density distribution

The polymer density distribution of a polyamide membrane obtained by MD and the proposed random resistor network model for water and ion transport.

 

Recent Publications:

E. Dražević, K. Košutić, V. Kolev, V. Freger, Does hindered transport theory apply to desalination membranes? Environ. Sci & Technol.  48 (2014)  11471–11478

V. Kolev, V. Freger, Hydration, Porosity and Water Dynamics in the Polyamide Layer of Reverse Osmosis Membranes: a Molecular Dynamics Study, Polymer, 55 (2014) 1420-1426

O Nir, N. Fridman-Bishop, O Lahav, V Freger, Modeling pH variation in reverse osmosis, Water Res., 87 (2015) 328-335

N. Fridman-Bishop, O. Nir, O. Lahav, V. Freger, Predicting the rejection of major seawater ions by spiral-wound nanofiltration membranes, Environ. Sci & Technol., 49 (14) (2015) 8631-8638

V. Kolev, V. Freger, Molecular dynamics investigation of ion sorption and permeation in desalination membranes, J. Phys. Chem. B, 119 (2015) 14168–14179

Membrane Modification

(Maria Bass, Katie Baransi-Karkaby, Shiran Shultz)

The selective layer of RO and NF membranes is usually slightly hydrophobic. This helps remove salts, but causes various problems, e.g.,  membrane foul by organics and biofilms and poorly remove some uncharged contaminants (bisphenol-A, boric acid etc.). We improve the selectivity towards contaminants and reduce propensity to fouling and facilitate cleaning by grafting a thin layer of acrylic polymer on the polyamide surface. We also insert certain molecules into polyamide structure to improve selectivity.

 polyamide structureprinciple of grafting –  the coating (blue) changes surfaces properties and seals imperfections of the polyamide layer underneath

Plugging for Banother principle –  insertion of “plug” molecules into polyamide as a way to enhance selectivity

 insertion of "plug" molecules into polyamidea STEM cross-section of a modified NF membrane showing the coating (dark) covering a thin polyamide layer (bright line)  on top of a porous support (light grey).

chart before and after modificationEffect of surface grafting on removal of several representative contaminants. Note the log scale for the vertical axis.

 

Recent Publications:

M. Bass, V. Freger, Facile evaluation of coating thickness on membranes using ATR-FTIR. J. Membr. Sci., 492 (2015) 348-354

Fouling, biofouling and bacterial deposition

(Maria Bass, Katie Baransi-Karkaby, Eli Margalit)

Bacteria may stick to and colonize nearly every surface by forming biofilms. In membrane processes this leads to membrane biofouling, which very difficult to predict and control.  The first critical step of biofouling is deposition and adhesion of bacteria to the surface.  We study and model the mechanism of bacterial deposition experimentally (QCM-D, parallel plate chambers) and theoretically, with the purpose to understand how it is related to the properties of the surface and to biofouling and how to modify surfaces to minimize their fouling. This work includes collaboration with colleagues from BGU, Technion, Germany and Korea.

stages of biofilm formationstages of biofilm formation; stage 1 is initial deposition.

a parallel plate flow cella parallel plate flow cell (PPFC) for studying deposition.

a setup for studying deposition

a setup for studying deposition with a PPFC mounted under microscope

numerical simulations can predict well bacterial deposition data

numerical simulations can predict well bacterial deposition data

 

Recent Publications:

I.  Marcus, M. Herzberg, S. Walker, V. Freger, Pseudomonas aeruginosa attachment on QCM-D Sensors: The role of cell and surface hydrophobicities, Langmuir, 28 (15) (2012) 6396–6402

E. Margalit, A. Leshansky, V. Freger, Modeling and analysis of hydrodynamic and physicochemical effects in bacterial deposition on surfaces, Biofouling, 28 (8) (2013)  977-989

R. Bernstein, V. Freger, J.-H. Lee, Y.-G. Kim, J. Lee, M. Herzberg, “Should I stay or should I go?”: Bacterial attachment versus biofilm formation on surface-modified membranes, Biofouling,  30 (2014) 367–376

“Next-Generation” Membranes

Membranes are a mature field and the performance of current membranes is often good. Nevertheless, we always seek for still better performance and novel, currently unavailable, types of membranes, which requires new research and unorthodox approaches. We are working on a few such projects, such as development of biomimetic membranes based on aquaporins (water channel membrane proteins used by all living organisms) and so-called mosaic and other novel nanofiltration membranes that have a uniquely high permeability to salts.

Biomimetic  Membranes and Microfluidics

(Rona Ronen, Yair Kaufman)

Inspired by unique characteristics of biological membranes and aquaporins, we explore how to make biomimetic ones. For this purpose we design and use supported biomimetic structures and study them in dedicated microfluidic cells.

Recent Publications:

Y. Kaufman, R. Kasher, R G.H. Lammertink, V. Freger, Microfluidic NF/RO Separation: Cell Design, Performance and Application, J. Membr. Sci., 396 (2012) 67-73

Y. Kaufman, S. Grinberg, C. Linder, E. Heldman, J. Gilron, V. Freger, Fusion of Bolaamphiphile Micelles: A method  to prepare stable supported biomimetic membranes, Langmuir, 29 (2013) 1152–1161

Y. Kaufman, S. Grinberg, C. Linder, E. Heldman, J. Gilron, Yue-xiao Shen, M. Kumar, V. Freger, Towards Supported Bolaamphiphile Membranes for Water Filtration: Role of Lipid-Support Interactions, J. Memb. Sci., 457 (2014)  50–61

R. Ronen, Y. Kaufman, V. Freger, Array of Pore-Spanning Lipid Membranes: Membrane Formation Mechanism and Water/Ion Transport, submitted
photoNovel Nanofiltration Membranes for Water Recycling

(Stanislav Levchenko)

We develop novel desalination membranes with uniquely high permeation of multivalent ions, highly beneficial for water recycling using the principle of mosaic membranes and other approaches. Such novel membrane will help to reduce membrane scaling, recover more water for irrigation, and save on chemicals and fertilizers for agriculture.

phohocurrent NF membranes completely remove hardness calcium and phosphate from secondary wastewater, resulting in severe scaling and low recovery.

 

photoa commercial NF  gets scaled and looses permeability (blue line), while a novel membrane has a better balanced Ca and PO4  rejection vs NaCl rejection and flux remains stable (red line).

 

photoThe principles of mosaic membrane and high salt permeability: cations and anions permeate through different nanodomains.

Membranes for fuel cells

(Robert Gloukhovski, Maria Bass)

A proton conducting membranes is at the heart of fuel cells of PEFC type. At present Nafion is the benchmark membranes material that combines high chemical stability and good proton conductivity. Nafion is composed of elongated polymeric micelles that can be aligned to enhance conductivity in the required direction, as well as stability and selectivity of Nafion.  We study various fundamental questions related to Nafion structure and its alignment using theoretical modeling and structural characterization methods, especially, surface-sensitive. Presently, in collaboration with Prof. Y. Tsur we explore embedding Nafion in nanopores of solid porous membranes, which serve as a template for aligning Nafion micelles.

Recent Publications:

V. Freger, Hydration of Ionomers and Schroeder’s Paradox in Nafion, J. Phys. Chem. B, 113(1) (2009) 24-36

M. Bass, A. Berman, A. Singh, O. Konovalov, V. Freger, Surface-induced orientation of micelles in films of Nafion, Macromolecules, 44 (2011) 2893–2899

R. Gloukhovski, V. Freger, Y. Tsur, A novel composite Nafion/Anodized Aluminium Oxide proton exchange membrane, accepted to Fuel Cells

photo

Alignment of Nafion micelles next to different surfaces and interfaces (after Bass et al., 2011)

 

photo

Straight nanopores of an Anodisc alumina membranes, in which Nafion micelles may be aligned