Tris(2-aminoethyl)amine in-situ modified thin-film composite membranes for forward osmosis applications

Photothermal-Assisted Interfacial Polymerization toward Microstructure Regulation of a Polyamide Membrane with Enhanced Separation Performance

A highly permeable thin-film composite (TFC) polyamide membrane with efficient salt rejection is valuable for numerous industrial processes. To achieve this objective, it is essential to innovate the membrane fabrication process to produce an ultrathin polyamide separation layer. In this study, a photothermal-assisted interfacial polymerization (IP) strategy was proposed to fabricate TFC polyamide membranes by incorporating carboxylated carbon nanotubes (CNTs) with exceptional photothermal properties. CNTs absorb solar energy and convert it into heat, significantly elevating the temperature in their microregions, thereby accelerating the reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC) during the IP process. Exploiting the self-inhibition characteristics of IP, the preformed polyamide layer suppresses the subsequent diffusion of MPD into the reaction interface, resulting in the formation of an ultrathin polyamide layer. Consequently, the CNTs-modified polyamide membrane with photothermal assistance obtains a thickness of approximately 94 nm, significantly thinner than the control membrane (189 nm). Furthermore, it demonstrates a superior water flux of 54.4 L m-2 h-1, higher than that of the pristine TFC membrane without CNTs and the conventional CNTs-modified membrane, while maintaining a NaCl rejection of ∼96%. The photothermal-assisted IP strategy provides some inspiration for engineering high-performance polyamide membranes available in various advanced separations.

Recent advances in surface tailoring of thin film forward osmosis membranes: A review

The recent advancements in fabricating forward osmosis (FO) membranes have shown promising results in desalination and water treatment. Different methods have been applied to improve FO performance, such as using mixed or new draw solutions, enhancing the recovery of draw solutions, membrane modification, and developing FO-hybrid systems. However, reliable methods to address the current issues, including reverse salt flux, fouling, and antibacterial activities, are still in progress. In recent decades, surface modification has been applied to different membrane processes, including FO membranes. Introducing nanochannels, bioparticles, new monomers, and hydrophilic-based materials to the surface layer of FO membranes has significantly impacted their performance and efficiency and resulted in better control over fouling and concentration polarization (CP) in these membranes. This review critically investigates the recent developments in FO membrane processes and fabrication techniques for FO surface-layer modification. In addition, this study focuses on the latest materials and structures used for the surface modification of FO membranes. Finally, the current challenges, gaps, and suggestions for future studies in this field have been discussed in detail.

Constructing dense and hydrophilic forward osmosis membrane by cross-linking reaction of graphene quantum dots with monomers for enhanced selectivity and stability

This paper reports a novel thin-film nanocomposite (TFN) membrane with a dense, flat, and hydrophilic polyamide (PA) layer. The atypical PA structure was obtained by the cross-linking reaction of graphene oxide quantum dots containing amino groups (NH₂-GOQDs) with triacyl chloride and polyamide oligomers. And the resulting TFN membrane showed a flat (small-scale ridge structure) and smooth surface. Meanwhile, the introduction of oxygen-containing and amino functional groups increased surface hydrophilicity. The reaction of amino groups on the NH₂-GOQDs with acid chloride groups and the carboxyl groups (in the linear part of the polyamide) enhanced the degree of cross-linking of the PA layer, forming a compact surface. Owning to the dense surface structure, excellent hydrophilicity, and small water transmission distance, the optimized TFN membrane exhibited an enhanced water flux of 26.57 L⋅m^-2⋅h^-1 with a low reverse salt flux of 6.0 g⋅m^-2⋅h^-1. Furthermore, nano-indentation/scratch results showed the interface adhesion between substrate and PA layer was improved due to the physical anchoring of NH₂-GOQDs in the substrate. And in the long-term FO test, the TFN membrane showed stable selectivity. This work proves that the targeted structural design of the PA layer at the nanoscale will have a positive impact on desalination field.

Tailoring Charged Nanofiltration Membrane Based on Non-Aromatic Tris(3-aminopropyl)amine for Effective Water Softening

High-performance positively-charged nanofiltration (NF) membranes have a profound significance for water softening. In this work, a novel monomer, tris(3-aminopropyl)amine (TAEA), with one tertiary amine group and three primary amine groups, was blended with trace amounts of piperazine (PIP) in aqueous solution to fabricate a positively-charged NF membrane with tunable performance. As the molecular structures of TAEA and PIP are totally different, the chemical composition and structure of the polyamine selective layer could be tailored via varying the PIP content. The resulting optimal membrane exhibited an excellent water permeability of 10.2 LMH bar⁻¹ and a high rejection of MgCl₂ (92.4%), due to the incorporation of TAEA/PIP. In addition, this TAEA NF membrane has a superior long-term stability. Thus, this work provides a facile way to prepare a positively charged membrane with an efficient water softening ability.

Self-Cleaning Nanofiltration Membranes by Coordinated Regulation of Carbon Quantum Dots and Polydopamine

Performance declination of nanofiltration (NF) membranes caused by concentration polarization (CP) and membrane fouling has severely restricted their practical application in many fields. This work reports the construction of a novel interlayer between the substrate and the selective layer of conventional composite membranes by coordinating regulation of carbon quantum dots (CQDs) and polydopamine (PDA). Unlike traditional methods that treat CP and fouling separately, the new strategy grants the membrane with dual functions at one time. First, the insertion of the PDA-CQDs layer reformulates the interfacial polymerization process that reduces the solute transport resistance and mitigates the CP issue. Second, the sandwiched photoactive CQDs can degrade organic molecules adsorbed on the membrane surface under visible light, which is promising for low-cost fouling remediation. This study may offer valuable insights into the preparation of durable self-cleaning NF membranes for the effective treatment of complex wastewater in various industries.

A Bifunctional Zwitterion That Serves as Both a Membrane Modifier and a Draw Solute for Forward Osmosis Wastewater Treatment

Producing clean water and simultaneously recovering valuable compounds are a big challenge in wastewater treatment. Here we designed a bifunctional zwitterion of (1-(3-aminopropyl)imidazole) propanesulfonate (APIS) for membrane modification and being a draw solute as well for water production and protein enrichment via forward osmosis (FO). Immobilized to the membrane surface by a fast amidation reaction, APIS endows the membrane with favorable properties benefiting the FO process. The APIS-modified sulfonated poly(ether sulfone) (APIS-sPES) membrane produces a water flux 101% higher than that of the nascent membrane (from 9.3 to 18.7 LMH) with 0.5 M NaCl as the draw solution. The APIS-sPES membrane also exhibits higher fouling resistance with a much smaller decline in water permeation and stronger renewability with the flux restored to 88% of the original value compared to a 59% recovery rate of the nascent membrane after 20-h experiments against a 200 ppm ovalbumin solution. APIS produces a fair good water flux coupled with negligible reverse diffusion when used as a draw solute and can be readily regenerated via pH regulation. Unlike the conventional NaCl draw solute, APIS does not contaminate or damage protein structure. The APIS-sPES membrane and APIS draw solute prove a perfect match in protein-containing wastewater treatment and protein enrichment.

Layer-by-layer self-assembly of pillared two-dimensional multilayers

We report Layer-by-Layer (LbL) self-assembly of pillared two-dimensional (2D) multilayers, from water, onto a wide range of substrates. This LbL method uses a small molecule, tris(2-aminoethyl) amine (TAEA), and a colloidal dispersion of Ti₃C₂T_x MXene to LbL self-assemble (MXene/TAEA)_n multilayers, where n denotes the number of bilayers. Assembly with TAEA results in highly ordered (MXene/TAEA)_n multilayers where the TAEA expands the interlayer spacing of MXene flakes by only ~ 1 Å and reinforces the interconnection between them. The TAEA-pillared MXene multilayers show the highest electronic conductivity of 7.3 × 10⁴ S m^-1 compared with all reported MXene multilayers fabricated by LbL technique. The (MXene/TAEA)_n multilayers could be used as electrodes for flexible all-solid-state supercapacitors delivering a high volumetric capacitance of 583 F cm^-3 and high energy and power densities of 3.0 Wh L^-1 and 4400 W L^-1, respectively. This strategy enables large-scale fabrication of highly conductive pillared MXene multilayers, and potentially fabrication of other 2D heterostructures.

Thin film nanocomposite hollow fiber membranes comprising Na+-functionalized carbon quantum dots for brackish water desalination

We have incorporated Na⁺-functionalized carbon quantum dots (Na-CQDs) into the polyamide layer via interfacial polymerization reaction and developed novel thin film nanocomposite (TFN) hollow fiber membranes for brackish water desalination. Comparing with the conventional thin film composite (TFC) membranes, the TFN membranes comprising Na-CQDs have a larger effective surface area, thinner polyamide layer and more hydrophilic oxygen-containing groups in the polyamide layer. Besides, the interstitial space among the polyamide chains becomes larger due to the presence of Na-CQDs. As a result, the incorporation of 1 wt% Na-CQDs into the polyamide layer could improve the pure water permeability (PWP) of the membranes from 1.74 LMH/bar to 2.56 LMH/bar by 47.1% without compromising their NaCl rejection of 97.7%. Interestingly, stabilization of the TFN hollow fiber membranes containing 1 wt% Na-CQDs at 23 bar could further promote the PWP to 4.27 LMH/bar and the salt rejection to 98.6% under the same testing conditions due to the deformation of the membranes under a high hydraulic pressure. When using a 2000 ppm NaCl aqueous solution as the feed, the optimal water flux and rejection of the newly developed TFN membranes at 15 bar are 57.65 ± 3.26 LMH and 98.6% ± 0.35% respectively. The Na-CQDs incorporated TFN hollow fiber membranes show promising applications in the field of brackish water desalination.

Interfacial Polymerization of Zwitterionic Building Blocks for High-Flux Nanofiltration Membranes

A simple scalable strategy is proposed to fabricate highly permeable antifouling nanofiltration membranes. Membranes with a selective thin polyamide layer were prepared via interfacial polymerization incorporating building blocks of zwitterionic copolymers. The zwitterionic copolymer, poly(aminopropyldimethylaminoethyl methacrylate)- co-poly(sulfobetaine methacrylate) with an average molecular weight of 6.1 kg mol^-1, was synthesized in three steps: (i) polymerization of dimethylaminoethyl methacrylate to yield the base polymer by atom transfer radical polymerization (ATRP), (ii) fractional sulfobetainization via quaternization, and (iii) amination via quaternization. The effect of the zwitterionic polymer content on the polyamide surface characteristics, fouling resistance, and permeance is demonstrated. The zwitterion-modified membrane becomes more hydrophilic with lower surface roughness, as the zwitterionic polymer fraction increases. The excellent fouling resistance of the zwitterion-modified membrane was confirmed by the negligible protein adsorption and low bacteria fouling compared to a pristine membrane without zwitterionic segments. In addition, the zwitterion-modified membranes achieve a water permeation around 135 L m^-2 h^-1bar^-1, which is 27-fold higher than that of the pristine membrane, along with good selectivity in the nanofiltration range, confirmed by the rejection of organic dyes. This permeance is about 10 times higher than that of other reported loose nanofiltration membranes with comparable dye rejection. The newly designed membrane is promising as a highly permeable fouling resistant cross-linked polyamide network for various water treatment applications.

A low-cost and high-performance thin-film composite forward osmosis membrane based on an SPSU/PVC substrate

A low-cost sulfonated polysulfone (SPSU)/poly(vinyl chloride) (PVC) substrate based high-performance thin-film composite (TFC) forward osmosis (FO) membrane was fabricated in this work. The results showed that the morphologies of the substrates were looser and more porous, and the porosity, pure water permeability, surface hydrophilicity, and average pore size of the substrates significantly improved after the SPSU was introduced into the PVC substrates. Furthermore, the SPSU/PVC-based TFC membranes exhibited rougher, looser and less crosslinked polyamide active layers than the neat PVC-based TFC membrane. The water permeability obviously increased, and the structure parameter dramatically declined. Moreover, the FO performance significantly improved (e.g. the water flux of TFC2.5 reached 25.53/48.37 LMH under FO/PRO mode by using 1.0 M NaCl/DI water as the draw/feed solution, while the specific salt flux exhibited a low value of 0.10/0.09 g/L). According to the results, it can be concluded that 2.5% of SPSU was the optimal blend ratio, which exhibited the lowest sulfonated material blend ratio compared to the data reported in the literature. Hence, this is a feasible and low-cost fabrication approach for high-performance FO membrane by using the cheap PVC and low blend-ratio SPSU as the membrane materials.

High-performance thin-film composite forward osmosis membrane fabricated on low-cost PVB/PVC substrate

The incorporation of the PVB significantly improved the performance of the PVB/PVC substrates based thin-film composite forward osmosis membrane.