Synthetic polymer membranes are enabling components in key technologies at the water–energy nexus, including desalination and energy conversion, because of their high water/salt selectivity or ionic conductivity. However, many applications at the water–energy nexus require ion selectivity, or separation of specific ionic species from other similar species. Here, the ion selectivity of conventional polymeric membrane materials is assessed and recent progress in enhancing selective transport via tailored free volume elements and ion–membrane interactions is described. In view of the limitations of polymeric membranes, three material classes—porous crystalline materials, 2D materials, and discrete biomimetic channels—are highlighted as possible candidates for ion‐selective membranes owing to their molecular‐level control over physical and chemical properties. Lastly, research directions and critical challenges for developing bioinspired membranes with molecular recognition are provided.
Minimizing the energy consumption
of desalination processes is
an important goal for augmenting freshwater production and mitigating
water scarcity. Chemical, civil, mechanical, and environmental engineering
students can derive and analyze the energy consumption of desalination
processes by applying engineering fundamentals such as thermodynamics,
transport phenomena, and process design. We explore the fundamental
thermodynamic limits of the most prominent desalination technologies
in a format designed for engineering students and instructors. Two
thermodynamically reversible processes for reverse osmosis (RO) and
electrodialysis (ED) are developed to demonstrate that reversible
processes consume the theoretical minimum energy, which is the Gibbs
free energy of separation. We then quantify the practical minimum
energy consumption for RO and ED, showing that the energy consumption
of these processes approaches the minimum thermodynamic limit with
increased process staging.
Despite decades of dominance in separation
technology, progress
in the design and development of high-performance polymer-based membranes
has been incremental. Recent advances in materials science and chemical
synthesis provide opportunities for molecular-level design of next-generation
membrane materials. Such designs necessitate a fundamental understanding
of transport and separation mechanisms at the molecular scale. Molecular
simulations are important tools that could lead to the development
of fundamental structure–property–performance relationships
for advancing membrane design. In this Perspective, we assess the
application and capability of molecular simulations to understand
the mechanisms of ion and water transport across polymeric membranes.
Additionally, we discuss the reliability of molecular models in mimicking
the structure and chemistry of nanochannels and transport pathways
in polymeric membranes. We conclude by providing research directions
for resolving key knowledge gaps related to transport phenomena in
polymeric membranes and for the construction of structure–property–performance
relationships for the design of next-generation membranes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.