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  1. Abstract Polymer membranes have been used extensively for Angstrom-scale separation of solutes and molecules. However, the pore size of most polymer membranes has been considered an intrinsic membrane property that cannot be adjusted in operation by applied stimuli. In this work, we show that the pore size of an electrically conductive polyamide membrane can be modulated by an applied voltage in the presence of electrolyte via a mechanism called electrically induced osmotic swelling. Under applied voltage, the highly charged polyamide layer concentrates counter ions in the polymer network via Donnan equilibrium and creates a sizeable osmotic pressure to enlarge the free volume and the effective pore size. The relation between membrane potential and pore size can be quantitatively described using the extended Flory-Rehner theory with Donnan equilibrium. The ability to regulate pore size via applied voltage enables operando modulation of precise molecular separation in-situ. This study demonstrates the amazing capability of electro-regulation of membrane pore size at the Angstrom scale and unveils an important but previously overlooked mechanism of membrane-water-solute interactions. 
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    Free, publicly-accessible full text available December 1, 2024
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  6. Advantages of various membrane-based desalination processes are compared by analyzing driving forces and transport principles. 
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    Free, publicly-accessible full text available January 6, 2024
  7. null (Ed.)
    Seawater desalination has become an important tool to attain global water security and sustainability. Among the available technologies, reverse osmosis (RO) has become the golden standard for seawater desalination due to its unparalleled energy efficiency. While RO is already efficient after development for half a century, there remains room for over 50% further reduction in energy consumption that can translate into tens of terawatt hours of potential annual energy saving. However, this significant energy saving cannot be achieved under the conventional paradigm of on-ground RO. In this analysis, we assess the idea of operating RO with open modules several hundred meters below the ocean surface ( i.e. , the mesopelagic zone). This new process, namely mesopelagic open reverse osmosis (MORO), can potentially push the energy consumption of seawater desalination to its theoretical limit. We first describe the concept of MORO, and then examine both the theoretical potential of energy saving and the practical challenges facing the implementation of MORO. Our analysis provides a theoretical framework for the future development of MORO for more sustainable desalination. 
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  8. null (Ed.)