Omnifarious performance promotion of the TFC NF membrane prepared with hyperbranched polyester intervened interfacial polymerization

Highly Permeable Nanofibrous Composite Nanofiltration Membranes by Controllable Interfacial Copolymerization

An ultrathin nanofibrous composite nanofiltration (NF) membrane was developed through controlled interfacial copolymerization where an electrospun sulfonated poly(ether sulfone) (SPES) nanofibrous membrane serves as the substrate and 2,5-diaminobenzenesulfonic acid (2,5-DABSA) and piperazine (PIP) serve as aqueous phase monomers. The integration of the electrostatic interaction and hydrogen bonding between SPES nanofibers and PIP/2,5-DABSA triggered the controlled diffusion rate of monomers into the organic phase, resulting in the fabrication of an ultrathin polyamide barrier layer (∼56 nm). Additionally, a polyamide structure was created through the ternary interfacial copolymerization of PIP/2,5-DABSA and trimesoyl chloride (TMC), which offers high permeability to the composite NF membrane. Meanwhile, the -SO3H groups on 2,5-DABSA issued highly negative charges to the polyamide barrier layer, leading to a significant improvement in the rejection ratio against SO42- and fouling resistance against bovine serum albumin. The impact of 2,5-DABSA monomer on the cross-linking degree and pore size distribution of the polyamide barrier layer was investigated by optimizing the proportion of PIP and 2,5-DABSA monomers in the interfacial polymerization (IP) process. The ion selectivity and robustness of the composite NF membrane was determined and compared with conventional and commercial NF membranes comprehensively. Molecular dynamics simulations were conducted to demonstrate the mechanism of the controlled diffusion of monomers; the cross-linking degree and fractional free volume of the polyamide barrier layer were also evaluated. The NF-M(1:1) composite membrane exhibited a significant enhancement in the permeation flux as 137.4 L/m2·h at 0.5 MPa, which was 4 times higher than that of conventional NF membranes, while maintaining excellent divalent salt rejection against Na2SO4 at 99.4%, compared with 98.0% of the conventional NF membrane, effectively breaking through the trade-off effect in the long-term filtration performance.

Nanofiltration Membrane with Enhanced Ion Selectivity Based on a Precision-Engineered Ultrathin Polyethylene Supporting Layer

Nanofiltration (NF) technology is increasingly used in the water treatment and separation fields. However, most research has focused on refining the selective layer while overlooking the potential role of the supporting layer. With expertise in ultrathin polymer films, particularly in the production of polyethylene (PE) membranes, we explore the possibility of improving NF membrane performance by precisely controlling the structure and surface properties of the ultrathin supporting layer in this work. Here, we introduced an innovative NF membrane that used a submicrometer ultrathin PE membrane produced through a biaxial stretching process, which is significantly thinner than commercial PE membranes available on the market. The core innovations are as follows: first, we focused on precise control of the supporting layer rather than just the selective layer, achieving significant enhancements in overall NF membrane performance; second, the ultrathin PE supporting layer served as a tunable interface for interfacial polymerization, offering possibilities for structural control of the selective layer and advancing membrane performance innovations. The resulting NF membrane boasts an overall thickness of ∼630 nm, which represents the thinnest NF membrane documented to date. This ultrathin NF membrane showed an ultrahigh Cl-/SO42- selectivity of 338.03, placing it at the forefront of existing literature. This study sheds light on the important role of the supporting layer in the preparation of selective layers. We believe that this approach has the potential to contribute to the development of ultrathin, high-performance NF membranes.

Synergistic interfacial polymerization between hydramine/diamine and trimesoyl chloride: A novel reaction for NF membrane preparation

Polyester-amide (PEA) thin film composite (TFC) NF membranes have rapidly evolved towards a competitive performance, benefiting from their remarkable antifouling capability and superior chlorine resistance. In this report, a new concept of synergistic interfacial polymerization is explored, which promptly triggers the reaction between hydramines and trimesoyl chloride (TMC) in the presence of a trace amount of diamines. This rapid-start mode enables the formation of defect-free PEA films without the requirement of catalysis. A comprehensive characterization of physicochemical properties using high-resolution mass spectrometer (HRMS) reveals that the recombination and formation of a "hydramine-diamine" coupling unit plays a decisive role in activating the synergistic interfacial polymerization reaction with TMC molecules. Taking the pair of serinol and piperazine (PIP) as an example, the PEA-NF membrane fabricated with 0.1 w/v% serinol mixed with 0.04 w/v% PIP as water-soluble monomer and 0.1 w/v% TMC as oil phase monomer was found to have a pure water permeability (PWP) of 18.5 L·m-2·h-1·bar-1 and a MgSO4 rejection of 95.5 %, which surpasses almost all the reported PEA NF membranes. Findings of the current research provide more possibilities for the low-cost and rapid synthesis of high-performance PEA membranes aiming for water purification.

Enhancing membrane separation performance in the conditions of different water electrical conductivity and fouling types via surface grafting modification of a nanofiltration membrane, NF90

A commercialized and widely applied nanofiltration membrane, NF90, was in-situ modified through a surface grafting modification method by using 3-sulfopropyl methacrylate potassium salt and initiators. The effects of water electrical conductivity (EC) and fouling types on membrane separation efficiency were examined before and after membrane modification. Results reveal that both the pristine membrane (PTM) and surface grafting modification membrane (SGMM) had a declining permeate flux and salt (NaCl) removal efficiency but an increasing trend of pharmaceuticals and personal care products (PPCPs) removal with increasing water EC from 250 to 10,000 μs cm-1. However, SGMM exhibited a slightly declining permeate flux but 13%-17% and 1%-42% higher rejection of salt and PPCPs, respectively, compared with PTM, due to electrostatic repulsion and size exclusion provided by the grafted polymer. After sodium alginate (SA) and humic acid (HA) fouling, SGMM had 17%-26% and 16%-32% higher salt rejection and 1%-12% and 1%-51% greater PPCP removal, respectively, compared with PTM due to the additional steric barrier layer contributed by the foulants. The successful grafting and increasing hydrophilicity of the SGMM were confirmed by contact angle analysis, which was beneficial for mitigating membrane fouling. Overall, the proposed in-situ surface grafting modification of NF90 can considerably mitigate organic and biological fouling while raising the rejection of salt and PPCPs at different background water EC, which is beneficial for practical applications in producing clean and high quality water for consumers.

A review on polyester and polyester-amide thin film composite nanofiltration membranes: Synthesis, characteristics and applications

Nanofiltration (NF) membranes have been widely used in various fields including water treatment and other separation processes, while conventional thin film composite (TFC) membranes with polyamide (PA) selective layers suffer the problems of fouling and chlorine intolerance. Due to the abundant hydrophilic hydroxyl groups and ester bonds free from chlorine attack, the TFC membranes composed of polyester (PE) or polyester-amide (PEA) selective layers have been proven to possess enhanced anti-fouling properties and superior chlorine resistance. In this review, the research progress of PE and PEA nanofiltration membranes is systematically summarized according to the variety of hydroxyl-containing monomers for membrane fabrication by the interfacial polymerization (IP) reaction. The synthesis strategies as well as the mechanisms for tailoring properties and performance of PE and PEA membranes are analyzed, and the membrane application advantages are demonstrated. Moreover, current challenges and future perspectives of the development of PE and PEA nanofiltration membranes are proposed. This review can offer guidance for designing high-performance PE and PEA membranes, thereby further promoting the efficacy of nanofiltration.

Molecular Design of the Polyamide Layer Structure of Nanofiltration Membranes by Sacrificing Hydrolyzable Groups toward Enhanced Separation Performance

Nanofiltration (NF) is an effective technology for removing trace organic contaminants (TrOCs), while the inherent trade-off effect between water permeance and solute rejections hinders its widespread application in water treatment. Herein, we propose a novel scheme of "monomers with sacrificial groups" to regulate the microstructure of the polyamide active layer via introducing a hydrolyzable ester group onto piperazine to control the diffusion and interfacial polymerization process. The achieved benefits include narrowing the pore size, improving the interpore connectivity, enhancing the microporosity, and reducing the active layer thickness, which collectively realized the simultaneous improvement of water permeance and enhancement of TrOCs rejection performance. The resulting membranes were superior to both the control and commercial membranes, especially in water-TrOCs selectivity. The effects of using the new monomers on the membrane physicochemical properties were systematically studied, and underlying mechanisms for the enhanced separation performance were further revealed by simulating the polymerization process through density functional theory calculation and measuring the trans-interface diffusion rate of monomers. This study demonstrates a novel promising NF membrane synthesis strategy by designing the structure of reaction monomers for achieving excellent rejection of TrOCs with a low energy input in water treatment.

Dependable Performance of Thin Film Composite Nanofiltration Membrane Tailored by Capsaicin-Derived Self-Polymer

To address trade-off and membrane-fouling challenges during the development of nanofiltration membranes, a thin-film composite membrane was prepared on the basis of interfacial polymerization regulated by adjusting the capsaicin-derived self-polymer poly N-(2-hydroxy-5-(methylthio) benzyl) acrylamide (PHMTBA) on the polysulfone substrate in this study. Through the self-polymerization of the monomer HMTBA with varied contents, microwave-assisted technology was employed to develop a variety of PHMTBAs. It was discovered that PHMTBA is involved in the interfacial polymerization process. Piperazine and PHMTBA competed for the reaction with trimesoyl chloride, resulting in a flatter and looser membrane surface. The PHMTBA-modified membrane presented a typical double-layer structure: a thicker support layer and a thinner active layer. The addition of PHMTBA to membranes improved their hydrophilicity and negative charge density. As a result, the PHMTBA-modified membrane showed dependable separation performance (water flux of 159.5 L m⁻² h⁻¹ and rejection of 99.02% for Na₂SO₄) as well as enhanced anti-fouling properties (flux recovery ratio of more than 100% with bovine serum albumin-fouling and antibacterial efficiency of 93.7% against Escherichia coli). The performance of the prepared membranes was superior to that of most other modified TFC NF membranes previously reported in the literature. This work presents the application potential of capsaicin derivatives in water treatment and desalination processes.

Hyperbranched polymers as superior adsorbent for the treatment of dyes in water

The effective control on environmental pollutants is crucial for the proper management of diverse environmental systems (e.g., soil, water, and air). In this respect, the utility of various functional materials such as hyperbranched polymers (HPs) has been recognized due to their great potentil as adsorbent for the mitigation of numerous environmental pollutants. Here, we highlight the latest progress achieved in the design and construction of HPs with high adsorption potentials. We focus on adsorption mechanisms, functionalization methods, the role of functional groups in adsorption capacity, and the choice of HPs in adsorption of cationic and anionic dyes. Recent published reports are reviewed to quantify and qualify the removal efficiency of pollutants through adsorption. We also evaluate the adsorbing efficiency of the constructed HPs and compared their performance with other such systems. The utilization potential of new materials (magnetic, polar, and biological) is highlighted along with the methods needed for their preparation and/or modification (surface, end-group, and zwitterionic) for the construction of efficient adsorbing systems. Finally, the advantages and limitations of adsorbing systems are described along with the existing challenges to help establish guidelines for future research. This article is thus expected to offer new path and guidance for developing advanced HP-based adsorbents.