Polyamide membranes with nanoscale ordered structures for fast permeation and highly selective ion-ion separation

Abstract

Fast permeation and effective solute-solute separation provide the opportunities for sustainable water treatment, but they are hindered by ineffective membranes. We present here the construction of a nanofiltration membrane with fast permeation, high rejection, and precise Cl-/SO42- separation by spatial and temporal control of interfacial polymerization via graphitic carbon nitride (g-C3N4). The g-C3N4 nanosheet binds preferentially with piperazine and tiles the water-hexane interface as revealed by molecular dynamics studies, thus lowering the diffusion rate of PIP by one order of magnitude and restricting its diffusion pathways towards the hexane phase. As a result, membranes with nanoscale ordered hollow structure are created. Transport mechanism across the structure is clarified using computational fluid dynamics simulation. Increased surface area, lower thickness, and a hollow ordered structure are identified as the key contributors to the water permeance of 105 L m2·h−1·bar−1 with a Na2SO4 rejection of 99.4% and a Cl-/SO42- selectivity of 130, which is superior to state-of-the-art NF membranes. Our approach for tuning the membrane microstructure enables the development of ultra-permeability and excellent selectivity for ion-ion separation, water purification, desalination, and organics removal.

MOF-808/Polyamide Thin-Film Nanocomposite Membranes for Efficient Nanofiltration

“…Compared to the pristine TFC membrane (NF-0), the O/N ratios of the optimized TFN membranes are slightly lower, implying that the incorporation of nanoparticles increases the degree of cross-linking . This cross-linking degree may be related to the distribution of nanoparticles in the oil phase in which the preoccupancy of MOF-808 in the water–oil interface blocked the process of the IP reaction, and therefore the polyamide layer developed into a loose structure . However, when more excessive MOF-808s were incorporated, although this affected the polymerization of the polyamide, those nanoparticles aggregated on the membrane to form a cake-like layer, which will limit the transmission of water and will not be facilitated by the superiority of water permeance .…”

Interfacial polymerization at unconventional interfaces: an emerging strategy to tailor thin-film composite membranes

“…Techniques for adjusting film properties, such as the inclusion of additives, implementation of interlayers, design of monomer structures, addition of nanomaterials, and post-processing, are predominantly based on these interfaces to synthesize the polymer films, and the common method for creating these interfacial systems involves depositing the aqueous and organic phases on a flat substrate via dip-coating in sequential order. [24][25][26][27][28][29] Despite its numerous advantages, the conventional alkane-water interface encounters limitations when confronted with increasingly diverse separation requirements and heightened performance expectations.…”

Precise Regulation of Monomer Reactive Sites Enhances the Water Permeance and Membrane Selectivity of Polyamide Nanofiltration Membranes

“…While at a lower pH, the reduced nonprotonated PIP with more protonated species can lead to the formation of polyamide with less or ineffective cross-linking (Figure b,c). Indeed, several studies performed IP at different pH values to tailor membrane performance. − However, the critical role of the pH-regulated reactive sites on PIP monomers in polyamide properties and membrane performance has not yet been systematically investigated.…”