- Energy saving Nafion based nano filtration membranes
- Membranes for fuel cells
- Preparation, mechanics and fouling behavior of mesoscopic hydrogel coatings
- Mechanism of Salt Rejection in Membrane Desalination
- Membrane Modification
- Fouling, Biofouling and Bacterial Deposition
- “Next Generation” Membranes
- Biomimetic Membranes and Microfluidics
- Novel Mosaic NF Membranes for Water Recycling
- Membranes for Fuel Cells
Energy saving Nafion based nano filtration membranes
Ion selectivity of nanofiltration (NF) membranes is a critical factor in NF treatment scaling-prone of multi-ion effluents, such as wastewater. When removal of multivalent ions in such effluents is unnecessary or undesired, adjusting their rejection may mitigate scaling, in which case membranes combining oppositely charged electrolytes enable a tunable selectivity towards such ions. Here we report the preparation of a new tunable and highly stable polyelectrolyte complex NF membrane prepared by successively coating an ultrafiltration membrane support with negatively charged Nafion and positively charged polyvinylamine (PVAm) layers. While Nafion thickness controls the membrane permeability, the second PVAm coating is critical for eliminating defects in the Nafion layer and readily tunes the membrane net charge and, hence, ion selectivity via PVAm concentration in the coating solution. In this manner, a membrane with good permeability, balanced charge, and, therefore, equal (“symmetric”) rejection of divalent anions and cations is obtained. The membrane performance is unaffected by exposure to 10% salt in water; such remarkable stability for a polyelectrolyte-based membrane makes it potentially attractive for the treatment of wastewater effluents and brackish water sources.
Membranes for fuel cells
The proton conducting membrane is at the core of fuel cells of the PEFC type. Presently, Nafion is the gold standard membrane material that provides a high level of chemical stability and proton conductivity. Nafion with elongated polymeric micelles can be aligned in the through-membrane direction which enhancing the proton conductivity. In the early stage we explored Nafion structure and its alignment with the help of theoretical modeling and surface-sensitive structure characterization. Presently, we explore to fabricate the through-plane aligned proton exchange membrane using electrospinning technique and physical folding method in which protons can fast transfer through the aligned Nafion channels. We are attempting to develop the stable and competitive proton transfer channels in Nafion membranes.
Preparation, mechanics and fouling behavior of mesoscopic hydrogel coatings
Surfaces in an aqueous environment, such as water pipes, desalination membranes or even medical implants, are prone to macromolecular and bacterial attachment. We study polymeric coatings that can protect such surfaces from contamination, with a focus on cross-linked and swellable coatings known as hydrogels. After preparing uniform and defined hydrogel coatings, we measure their mechanochemical properties by atomic force microscopy. Then, we investigate the deposition behavior of model particles on the coatings. The goal is to gain a deeper understanding of foulant interactions with soft surfaces.
Mechanism of salt rejection in desalination membranes
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.
Given sea water composition, what will be the composition of permeate and retentate?
The polymer density distribution of a polyamide membrane obtained by MD and the proposed random resistor network model for water and ion transport.
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.
another principle – insertion of “plug” molecules into polyamide as a way to enhance selectivity
Fouling, biofouling and bacterial deposition
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.
a setup for studying deposition with a PPFC mounted under microscope
numerical simulations can predict well bacterial deposition data
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
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.
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
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.
Membranes for fuel cells
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.
R. Gloukhovski, V. Freger, Y. Tsur, A novel composite Nafion/Anodized Aluminium Oxide proton exchange membrane, accepted to Fuel Cells
Alignment of Nafion micelles next to different surfaces and interfaces (after Bass et al., 2011)
Straight nanopores of an Anodisc alumina membranes, in which Nafion micelles may be aligned