Molecular Insights into the Composition–Structure–Property Relationships of Polyamide Thin Films for Reverse Osmosis Desalination

Abstract

A molecular-level understanding of the structure–property relationship of polyamide (PA) active layers in thin-film-composite membranes remains unclear. We developed an approach to build and hydrate the PA layer in molecular dynamics simulations and reproduced realistic membrane properties, which enabled us to examine the composition–structure–permeability relationships at the molecular level. We discovered the variation of pore size distributions in the dry PA structures at different monomer compositions, leading to different water cluster distributions and wetting properties of hydrated PA films. Membrane swelling was linearly dependent on the degree of cross-linking (DC), and higher water flux was obtained in the more swelling-prone PA films because of the transition in water transport mechanisms. Continuum-like and jumping transport both occurred in PA films with smaller DC, where visible and more persistent channels existed. In the denser films, water molecules relied only on the on-and-off channels to jump from one cavity to another; however, jumping transport was more pronounced even in the less dense PA films, and all the PA structures exhibited oscillations, which provided evidence for the solution-diffusion model rather than the pore-flow model. The results not only contribute to fundamental understanding but also provide insights into the molecule-level design for next-generation membranes.

Molecular insights into the structure-property relationships of 3D printed polyamide reverse-osmosis membrane for desalination

“…Additionally, as viewed through the pore size distribution, many structures were inconsistent with one another. Zhang et al improved upon the existing methods by developing a repeatable and realistic MD model for PA membranes, which can reproduce the atomic composition, structure, and properties of dry and hydrated PA RO membranes in experiments [45]. Furthermore, their flexible method allowed them to tune the MPD/TMC ratio of the membrane during in silico fabrication.…”

High-Performance, Free-Standing Symmetric Hybrid Membranes for Osmotic Separation

“…Many efforts have been made to reduce ICP in previous research, such as adjusting the porosity, thickness, or tortuosity of porous support substrates to enhance the diffusion of the DS. − Nonetheless, because of the inherent asymmetric structure of current FO membranes, ICP cannot be eliminated by the abovementioned method. An ideal solution for eliminating ICP is to fabricate symmetric FO membranes without porous support substrates.…”

Application of Desalination Membranes to Nuclide (Cs, Sr, and Co) Separation

“… 24 Also, the RO membrane-based separation process is the key technology consistently providing clean water because of its high performance and cost efficiency. 25 …”

“…24 Also, the RO membrane-based separation process is the key technology consistently providing clean water because of its high performance and cost efficiency. 25 In this work, we describe the NF and RO techniques using commercial membranes for application in desalination and aqueous nuclide separation. Membranes used in NF and RO are studied to understand the physicochemical properties and permeation characteristics of aqueous nuclide solutions such as Cs, Sr, and Co in single and mixed streams.…”

“…NF membranes are widely applied for desalination and separation of wastewater to achieve low operation pressures and high permeation fluxes . Also, the RO membrane-based separation process is the key technology consistently providing clean water because of its high performance and cost efficiency …”