Unveiling the role of residual PVP in substrate-mediated interfacial structure regulation for high-performance polyamide nanofiltration membranes

How to understand the effects of heat curing conditions on the morphology and performance of polypiperazine-amide NF membrane

Nanofiltration (NF) membranes with outstanding performance are highly demanded for more efficient desalination and wastewater treatment. However, improving water permeance while maintaining high solute rejection by using the current membrane fabrication techniques remains a challenge. Herein, polyamide (PA) NF membrane with arch-bridge structure is successfully prepared via interfacial polymerization (IP) on a composite support membrane of salt-reinforced hydrophilic bacterial cellulose nanofibers (BCNs) nanofilm/polytetrafluoroethylene (BCNs/PTFE). The strong hydration of BCNs promotes Marangoni convection along water/organic solvent interface during the IP process, which creates extra area for interfacial reaction and produces a thin PA active layer with arch-bridge structures. These arch-bridge structures endow the resulting PA active layer with substantial larger active area for water permeation. Consequently, the PA NF membrane exhibits exceptional desalination performance with a permeance up to 42.5 L m−2 h−1 bar−1 and a rejection of Na2SO4 as high as 99.1%, yielding an overall desalination performance better than almost all of the state-of-the-art NF membranes reported so far in terms of perm-selectivity.

Polyamide (PA) nanofiltration (NF) membranes represent a promising approach to safe drinking water production. Yet, selective removal of contaminants while retaining essential minerals remains a critical challenge for cost-effective water treatment processes. Here, we employed ammonia bicarbonate (AB) as an economical additive to modify interfacial polymerization (IP) for developing high-performance NF membranes suitable for drinking water applications. Comprehensive characterization coupled with molecular dynamics simulations demonstrate that AB modulates the IP process through three mechanisms: (1) controlling the diffusion kinetics of piperazine (PIP) at the aqueous-organic interface, (2) the reaction between HCO3- and H+ produced by IP achieves nanofoaming, and (3) the thermal decomposition of AB releases additional gaseous products (NH3 and CO2), enhancing the dual nanofoaming effect. This controlled reaction kinetics and increased nanobubble formation produced a thinner, more wrinkled PA selective layer with an optimized microstructure. The optimized NF-AB-8 membrane demonstrated enhanced permeance (28.5 LMH/bar) during actual surface water purification, while maintaining selective separation between minerals and dissolved organic matter (KCa2+/DOM = 34.5). In addition, the improved microstructure and separation performance enhanced the antiscaling and antifouling properties of the NF membrane. This study explored the application of dual-nanofoaming mechanisms in NF membranes, providing insights for designing NF membranes that simultaneously improve permeance and selectivity, which may promote the preparation of high-performance NF membranes and their application in drinking water production.

An efficient co-solvent tailoring interfacial polymerization for nanofiltration: enhanced selectivity and mechanism

Double positively charged polyamide nanofiltration membrane with PEI/Zr4+ for Cr3+ and trimethoprim removal

Enhanced performance polyamide membrane by introducing high-porosity SOD/GO composite interlayer to tailor the interfacial polymerization process

High-performance and acid-resistant nanofiltration membranes prepared by solvent activation on polyamide reverse osmosis membranes

Hydrogel-regulated interfacial polymerization: A gateway to effective nanostructure tuning of polyamide nanofiltration membranes

The polyamide (PA) nanofiltration (NF) membrane has the potential to remove endocrine-disrupting compounds (EDCs) from water and wastewater to prevent risks to both the aquatic ecosystem and human health. However, our understanding of the EDC removal-water permeance trade-off by the PA NF membrane is still limited, although the salt selectivity-water permeance trade-off has been well illustrated. This constrains the precise design of a high-performance membrane for removing EDCs. In this study, we manipulated the PA nanostructures of NF membranes by altering piperazine (PIP) monomer concentrations during the interfacial polymerization (IP) process. The upper bound coefficient for EDC selectivity-water permeance was demonstrated to be more than two magnitudes lower than that for salt selectivity-water permeance. Such variations were derived from the different membrane-solute interactions, in which the water/EDC selectivity was determined by the combined effects of steric exclusion and the hydrophobic interaction, while the electrostatic interaction and steric exclusion played crucial roles in water/salt selectivity. We further highlighted the role of the pore number and residual groups during the transport of EDC molecules across the PA membrane via molecular dynamics (MD) simulations. Fewer pores decreased the transport channels, and the existence of residual groups might cause steric hindrance and dynamic disturbance to EDC transport inside the membrane. This study elucidated the trade-off phenomenon and mechanisms between EDC selectivity and water permeance, providing a theoretical reference for the precise design of PA NF membranes for effective removal of EDCs in water reuse.

Efficient capture of endocrine-disrupting compounds by a high-performance nanofiltration membrane for wastewater treatment

Construction of sub-10nm ultra-thin polyamide layer using porous GOQDs-AGQDs interlayer

Tailored design of highly permeable polyamide-based nanofiltration membrane via a complex-dissociation regulated interfacial polymerization

Corolliform morphology thin film composite polyamide membrane constructed via Tröger's base PIM for enhancing nanofiltration separation performances

Regulating the monomer diffusion during interfacial polymerization (IP) process is the key for tailoring the pore structure and desalination performance of thin‐film composite polyamide nanofiltration (NF) membrane. Recently a surfactant‐assembly strategy to regulate IP process and NF membranes with sub‐Å separation precision is proposed. However, little is known for the role of the molecular structure of surfactant on IP process and membrane performance. In this work, five sulfate surfactants with different length of alkyl chains are used to construct surfactant monolayer assembly at the water/hexane interface to regulate IP process. The results show that for the sulfate surfactants, the longer the alkyl chain, the more uniform the pore size distribution of polyamide active layer is and the higher the ion separation selectivity of NF membrane is. Among them, the NF membrane prepared from sodium n‐hexadecyl sulfate (SHS) exhibits the highest separation performance with the rejection of Na2SO4, MgSO4, MgCl2, and CaCl2 up to 99.39%, 99.12%, 98.09%, and 97.38%, respectively. Overall, this study further confirms the regulatory role of surfactant‐assembled monolayer during IP process and provides important insights into how the polyamide structure and the resulting NF membranes are influenced by the alkyl chain length of the surfactants.

Innovative role of polyvinylpyrrolidone in tailoring polyamide layer for high-performance nanofiltration membranes