Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly­(vinyl alcohol) (PVA) interlayered poly­(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES–PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m–2 h–1 bar–1 and a 99.4% Na2SO4 rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

A high-performance nanofiltration (NF) membrane with simultaneously improved desalination and antifouling properties while maintaining regeneration ability is highly desirable in water treatment. Surface modification is an effective approach to enhance the performance of NF membranes. In the present study, a multifunctional thin-film composite NF membrane (Fe–TFC) was fabricated via coating a regenerable ferric ion–tannic acid (FeIII–TA) layer on the nascent polyamide membrane surface. The Fe–TFC membrane exhibited enhanced hydrophilicity, smaller pore size, and lower negative charge compared with the control membrane. The salt rejections and selectivity of divalent to monovalent ions were greatly improved with only a slight decrease in water permeability due to the presence of the coating layer. Meanwhile, dynamic fouling tests with humic acid demonstrated that the Fe–TFC membrane possessed an enhanced antifouling property and excellent flux recovery rate. After coating, the normalized water flux and flux recovery of the Fe–TFC membrane increased from 0.02 to 0.26 and 32.1 to 76.4% at the end of five cycles of fouling tests, respectively. In addition, the resultant membrane exhibited excellent durability and stability under harsh conditions for ∼10 days. Interestingly, the fouled coating layer can be easily removed by HCl cleaning and regenerated through an in situ strategy. Consequently, the regenerated membranes presented stable antifouling properties and desalination performance after several times of regeneration. It was demonstrated that the unique feature of FeIII–TA networks enables the coating layer to act as a protective layer for the underlying polyamide membrane, leading to the high performance of the composite membrane. This study provides a new insight for surface functionalization and easy regeneration of the TFC nanofiltration membrane in water treatment technology.

Ferrous iron/peroxymonosulfate (Fe(II)/PMS) oxidation was employed as a pretreatment method for ultrafiltration process to control membrane fouling caused by natural organic matter, including humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA), and their mixture (HA-SA-BSA). To evaluate the mechanism of fouling mitigation, the effects of Fe(II)/PMS pretreatment on the characteristics of feed water were examined. The degradation of atrazine (ATZ) was also investigated and the species of generated radicals were preliminarily determined. Under the test exposure (15 and 50 μM), Fe(II)/PMS pretreatment effectively mitigated membrane fouling caused by HA, SA and HA-SA-BSA mixture, and the performance improved with the increase of Fe(II) or PMS dose; whereas aggravated BSA fouling at lower doses and fouling alleviation was observed only at a higher dose (50/50 μΜ). The fouling mitigation was mainly attributed to the effective reduction of organic loadings by coagulation with in-situ formed Fe(III). Its performance was comparable or even slightly higher than single coagulation with Fe(III), most likely due to the oxidation by Fe(II)/PMS process. Fe(II)/PMS oxidation showed better performance in reducing DOC and UV, fluorescence intensities of fluorescent components and UV-absorbing compounds than single coagulation. In addition, Fe(II)/PMS pretreatment was efficient in ATZ degradation due to the generation of sulfate and hydroxyl radicals, whereas coagulation was ineffective to remove it.

The demand for thin-film composite (TFC) nanofiltration membranes with superior permeance and high rejection is gradually increasing for seawater desalination and brackish water softening. However, improving the membrane permeance remains a great challenge due to the formation of excrescent polyamide in the substrate pores and thick polyamide film. Herein, we fabricated a highperformance TFC nanofiltration membrane via a classical interfacial polymerization reaction on a two-dimensional lamellar layer of transition-metal carbides (MXene). The MXene layer promoted the absorption of the reactive monomer, and higher amine monomer concentration facilitated the self-sealing and self-termination of interfacial polymerization to generate a thinner outer polyamide film from 68 to 20 nm. The almost nonporous lamellar interface inhibited the formation of inner polyamide in the substrate pores. In addition, the MXene lamellar layer could be eliminated by mild oxidation after interfacial polymerization to avoid imparted additional hydraulic resistance. The resulting TFC membrane conferred a high rejection above 96% for Na 2 SO 4 and excellent permeance of 45.7 L•m −2 •h −1 •bar −1 , which was almost 4.5 times higher than that of the control membrane (10.2 L•m −2 •h −1 •bar −1 ). This research provides a feasible strategy for fabricating a high-performance nanofiltration membrane using two-dimensional nanosheets as a templated interface.

Nanofiltration (NF) membranes have been widely applied in many important environmental applications, including water softening, surface/groundwater purification, wastewater treatment, and water reuse. In recent years, a new class of piperazine (PIP)-based NF membranes featuring a crumpled polyamide layer has received considerable attention because of their great potential for achieving dramatic improvements in membrane separation performance. Since the report of novel crumpled Turing structures that exhibited an order of magnitude enhancement in water permeance (Science2018360518521), the number of published research papers on this emerging topic has grown exponentially to approximately 200. In this critical review, we provide a systematic framework to classify the crumpled NF morphologies. The fundamental mechanisms and fabrication methods involved in the formation of these crumpled morphologies are summarized. We then discuss the transport of water and solutes in crumpled NF membranes and how these transport phenomena could simultaneously improve membrane water permeance, selectivity, and antifouling performance. The environmental applications of these emerging NF membranes are highlighted, and future research opportunities/needs are identified. The fundamental insights in this review provide critical guidance on the further development of high-performance NF membranes tailored for a wide range of environmental applications.