Efficient & Selective Ion Pumps based on Ratchet Mechanisms

Project Information

ESIP-RM

Grant agreement ID: 101039804

DOI

10.3030/101039804

EC signature date 17 February 2022

Start date 1 October 2022

End date 30 September 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 609 470,00

EU contribution

€ 1 609 470,00

Coordinated by

TEL AVIV UNIVERSITY
Israel

Periodic Reporting for period 1 - ESIP-RM (Efficient & Selective Ion Pumps based on Ratchet Mechanisms)

Reporting period: 2022-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

Ion selective separation with membrane-based processes may advance dramatically technologies for water treatment, resource extraction from sea water, ion specific sensors and many other applications. Moreover, since about 10-15% of the global energy consumption is used for chemical separations, a high efficiency, membrane-based ion separation processes can reduce greenhouse gas emissions significantly. However, membrane-based ion selective separation is a longstanding unmet challenge in science and engineering. Although conventional membrane-based separation is extremely efficient in unselective separation processes such as reverse osmosis water desalination, membrane-based processes showed limited success in ion specific separations. Furthermore, the need for a molecular level control of the membrane properties, limits the scalability of most of the membrane-based ion selective separation techniques that are currently being studied.
The goal of this project is to develop ratchet-based ion pumps for selective ion separation. These devices are driven with a ratchet mechanism which utilizes modulations of a spatially asymmetric electric field to induce a non-zero net ion flux up a concentration gradient. We utilize a fundamental ratchet process in which the ratchet input signal drives particles with the same charge but different transport properties in opposite directions, to design highly selective, fit-to-purpose, and real-time controlled ion separation systems thereby bypassing the limitations faced by current technologies.
In this research we combine theory, simulation and experiment to improve our understanding of the ratchet mechanism, design and optimize ratchet-based ion pumps, demonstrate ion selective ratchet-based separation systems, and set their thermodynamic performance limits.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We have shown by simulation of a simple sawtooth model that same-charged ions with a relative diffusion coefficient difference as small as 1% can be driven in opposite directions with a velocity difference as high as 1.2 mm/s. In this work we describe the transport mechanism that underlies ratchet-based ion separations, which is the frequency dependent velocity reversal, and the operating conditions that enable it. It was shown that this ability can pave the way for rapid extraction of trace ions from solutions, such as the case in Lithium extraction from sea water, where conventional membrane-based separation processes do not offer sufficient selectivity.
The next step is to realize more complex membranes structures that can allow a direct control of the spatial potential distribution. In a recent study, we presented a model for a stack-layered membrane that is composed of alternating electrodes that are separated by insulating layers in an asymmetric design. The model includes adjacent electrolyte reservoirs and ion-ion interactions, which were not accounted for in prior models, and thus provides a more realistic understanding of the driving mechanism and potential capabilities. It was shown that, unlike most other proposed ion pumps, the stacked-layered RBIP drives both cations and anions in the same direction and overcomes substantial concentration gradients. This makes the membrane an excellent candidate for distributed water desalination and bio-medical applications. Moreover, it was shown that velocity reversal is possible under more realistic conditions, making it possible to achieve extremely high ion-ion selectivity.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In our work we have combined concepts from two different disciplines (ratchets and ion separation), to conceive a new method for selective ion separation. Since this research is the first to connect ratchets with selective ion separation, all the results obtained are beyond the state of the art. Many of the terms, definitions, and performance metrics for ratchet driven ion selective ion pumping are also defined for the first time.
Our theory shows that selective ion separation using ratchets is unmatched in its ability to resolve specific ions, and to control its selectivity in real-time using simple electric signals. We provide the guidelines for ion separation with high resolution and how this method can be used for specific applications such as harvesting Lithium from sea water, heavy metal removal from drinking water, and separating monovalent ions such as Potassium from Sodium.
We also show that under standard conditions, ratchet-based ion pumps drive both cations and anions in the same direction, a process we term ambipolar pumping. This implies that ratchet-based ion pumps can be used for water desalination systems with no moving parts and do not rely on energy costly electrochemical reactions nor batch processes (as in electrodialysis and capacitive deionization). We show that ratchets in moderately saline water can drive ions up a five-fold concentration gradient with input signals with amplitudes below 1V. Thus, ratchet based ion pumping may be applicable for brackish water desalination.

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