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Acyl chloride monomers have been serving as the dominant acylation reagent for preparing thin‐film composite (TFC) nanofiltration (NF) membranes over the past few decades. Herein, a novel acylation reagent (trimellitic anhydride, TMA) was exploited in conjunction with trimesoyl chloride (TMC) to undergo interfacial polymerization with piperazine (PIP) on the polysulfone substrate membranes. The introduction of TMA enabled the deeper diffusion of PIP monomers into the organic phase, resulting in the creation of novel circular‐shaped protuberances on the top surface of the polyamide layer and the significant increase in the effective membrane area. Besides, abundant in‐situ carboxylic groups were generated in the polyamide layer, conducive to both the surface hydrophilicity and negative charge density. Consequently, with an addition of 0.03 wt% TMA, pure water flux reached up to 15.3 L m−2 hour−1 bar−1, almost 2.2 times that of the pristine membrane, and high rejection of Na2SO4 (97.3%) was maintained, evincing the superior desalination performance of the TMA‐modified membranes. The interaction mechanism between TMA, TMC, and PIP was described in detail. Furthermore, the TMA‐modified membranes exhibited a stable separation performance over the long‐running process. [ABSTRACT FROM AUTHOR]

Abstract: Based on the existing carboxylic acid groups on surface of used commercial thin film composite polyamide reverse osmosis membrane, two kinds of poly(ethylene glycol) derivatives with different chains were grafted by carbodiimide-induced method to improve the antifouling property. The membranes before and after modification were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and static contact angle measurement. Moreover, the water flux, NaCl rejection and fouling experiments were also conducted. The changes of chemical composition and morphology on membrane surfaces indicated the successful grafting of poly(ethylene glycol) derivatives. Compared to unmodified membrane, the modified membranes were more resistant to fouling in protein and cationic surfactant feeding solutions. The method in this study provided a new way for surface modification of commercial polyamide reverse osmosis membranes. [Copyright &y& Elsevier]

Abstract: A novel method of surface modification by grafting hydrophilic poly(ethylene glycol) (PEG) chains onto the surface of a thin-film composite (TFC) polyamide reverse osmosis (RO) membrane was performed. Aminopolyethylene glycol monomethylether (MPEG-NH2) was used as grafting monomer. The membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The changes in chemical composition and morphology of the membranes'' surface indicated the successful grafting process. Furthermore, a preliminary experiment confirmed that the grafting of PEG chains improved membrane antifouling property. [Copyright &y& Elsevier]

• The SWRO brine desalination process by a submerged vacuum membrane distillation system was investigated. • The reasons for flux attenuation were distinguished by the combination of experiment and theoretical calculation. • Flux attenuation could be alleviate by changing the operation mode. • NaCl Crystallization behavior was affected by both the existence of foreign ions and operation mode. This work studied the concentration of seawater reverse osmosis (SWRO) brine by a submerged vacuum membrane distillation (SVMD) process. Factors for flux attenuation including CaSO 4 crystallization,vapour pressure depression, the increase of heat transfer resistance and membrane fouling were distinguished by the combination of experiment and theoretical calculation. It was suggested that CaSO 4 crystallization was the main reason for flux attenuation, which should be eliminated by appropriate feed pretreatment with additional of Na 2 CO 3 and HCl. The combined effect of other three factors was another important reason for flux attenuation. Although the effect of CaSO 4 crystallization was eliminated, there still existed a critical VCF after which membrane fouling and increase of heat transfer resistance could not be neglected. The result indicated that this critical VCF was about 2.5 under the experimental condition, which was far less than the VCF at which NaCl solution reached saturation. Therefore, finding an effective method to mitigate membrane fouling was still necessary. It was concluded that decreasing the concentration rate by changing the operation mode could effectively increase the critical VCF to 3.7. Meanwhile, the crystallization behavior of NaCl and the size and quality of crystal products would be affected. [ABSTRACT FROM AUTHOR]

High-performance semi-permeable membranes play a vital role in the membrane-based separation technology for seawater and brackish water desalination. Herein, plasticizer-assisted interfacial polymerization (PAIP) was implemented to fabricate aromatic polyamide layers with improved water flux and comparable salt rejection for the first time. Specifically, plasticizer (i.e., diethyl phthalate, DEP) was introduced into the organic phase to perform interfacial polymerization. Effective regulation of the desalination performance was achieved via meticulously adjusting plasticizer concentration. With the addition of 0.5 wt% DEP, water flux promoted from 1.06 L m−2 h−1 bar−1 of the pristine membrane to 2.85 L m−2 h−1 bar−1, with NaCl rejection decreasing from 98.3% to 98.2%. With the addition of 1.5 wt% and 2.0 wt% DEP, water flux improved to 4.82 L m−2 h−1 bar−1 and 5.95 L m−2 h−1 bar−1, respectively, more than 4.5 and 5.5 times that of the pristine membrane. Nevertheless, NaCl rejection decreased to 96.6% and 95.9%, respectively. The infrared detection revealed that the introduction of DEP disrupted the original intermolecular hydrogen bonding between polyamide chains, thereby enhancing the softness of the polyamide layer, which was demonstrated by the decreased Young's modulus. As a result, the water diffusion efficiency through the polyamide layer was promoted, leading to the significant enhancement of water flux. These findings pave a new route for the synthesis of the aromatic polyamide layer with excellent desalination performance to expand the application of membrane technology. Image 1 • Plasticizer-assisted interfacial polymerization was developed to prepare RO membranes. • Polyamide chain flexibility improved substantially in the presence of plasticizer. • Disruption of inter chain hydrogen bonding caused enhancement of chain flexibility. • Water flux enhanced due to more efficient transport channels for water molecules. [ABSTRACT FROM AUTHOR]

The considerable permeability of fully-aromatic polyamide reverse osmosis (RO) membranes is believed to be strongly dependent on the presence of a mount of internal voids within the polyamide separation layer, which provides additional permeation channels in addition to diffusion through the polyamide matrix. Based on this understanding, herein, we reported a novel strategy of developing highly permeable RO membranes via introducing a void-tailoring agent, (3,3,3-trifluoropropyl)trichlorosilane (TFPTCS) into the traditional interfacial polymerization (IP) system composed of m-phenylenediamine and trimesoyl chloride. During IP process, the fast and violent hydrolysis and aminolysis of TFPTCS caused a significantly increasing pore size and porosity of the incipient polyamide film, which resulted in the formation of double- or multi-layer void structures with higher void fraction in the polyamide film. As a result, the TFPTCS added membrane showed a dramatic enhancement in water permeability, and the optimum condition was observed at the 0.03 wt% of TFPTCS concentration with 3.74 L m−2 h−1 bar−1, which was 2.8 times higher than that of the pristine membrane, while the salt rejection was almost unchanged (around 97.0%). These findings demonstrate the feasibility of void-tailoring inside the polyamide film, and encourage further exploration of new alternative void-tailoring agents to prepare highly permeable polyamide RO membranes for water desalination, which were seldom studied previously. • TFPTCS was introduced into the traditional MPD-TMC IP system to tune the internal void structure of the formed PA films. • The addition of TFPTCS led to an increase in the void volume within PA films, the pore size and porosity of PA back face. • The modified membrane showed a 2.8-fold improvement in water permeability without the loss of salt rejection. [ABSTRACT FROM AUTHOR]

Extraction of lithium from salt lakes is an important route for lithium sources. Due to the unique structure and separation mechanism, i.e., size exclusion and Donnan effect, nanofiltration (NF) is considered as a promising way to separate magnesium (Mg2+) and lithium (Li+) ions. However, the Mg2+/Li+ separation factor of NF membrane fabricated by traditional interfacial polymerization (IP) is usually dissatisfactory. Here, a swelling-embedding-shrinking strategy was proposed to modify polyethyleneimine (PEI)/trimesoyl chloride (TMC) NF membranes using diethylenetriamine (DETA) to improve the performance in Mg2+/Li+ separation. The pristine PEI/TMC NF membrane was swollen with methanol to increase the polyamide chain spacing followed by embedding electropositive DETA as a modifier. The charge properties and pore structure of the active layer could be regulated by optimizing the modification conditions. Within comparison to the pristine membrane (TFC-0), the pure water flux of modified NF membrane (TFC-3) increased by 63.6% because of the rougher surface and the larger pore size. Meanwhile, the embedding of electropositive DETA reduced the electronegative property of membrane surface. In consequence, TFC-3 membrane exhibited higher rejection of MgCl 2 (93.9% against 88.4%) and lower rejection of LiCl (31.0% against 32.1%), thus showing a twofold improvement in Mg2+/Li+ separation factor (S Li, Mg = 11.38 against 5.87). The swelling-embedding-shrinking strategy in this article provided a good reference for the modification of NF membranes in the separation of multivalent and monovalent ions. [Display omitted] • A swelling-embedding-shrinking strategy was proposed to enhance membrane performance. • Surface property and pore size could be regulated by embedding diethylenetriamine (DETA). • Modified PEI/TMC NF membrane had higher rejection of Mg2+ but lower rejection of Li+. • Mg2+/Li+ separation factor reached up to 11.38 compared to 5.87 of pristine membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • New polyamide layer with rigid-flexible microstructure was constructed. • Both internal pores and positive charge density were remolded at molecular level. • "Useless pores" were widened and "defect pores" were repaired simultaneously. • Modified membrane exhibited much higher Mg2+/Li+ selectivity factor of 15.38. Lithium extraction from salt-lake brine with a high Mg2+/Li+ ratio is crucial for mitigating lithium supply shortage. Positively charged polyamide nanofiltration membranes, which are often prepared by performing interfacial polymerization (IP) using polyethyleneimine and trimesoyl chloride, are considered to be promising candidates for Mg2+/Li+ separation owing to their high energy efficiency and low environmental impact. However, the performance of these membranes is severely hindered by "useless pores" and "defects" present in the flexible polyamide layer. Herein, we provide a facile strategy for modifying flexible semi-aromatic polyamide chains by intercalating a rigid electropositive monomer, histamine, to remold the internal pores and positive charge density at a molecular level. Two routes, namely, "swelling-embedding-reacting-shrinking (SERS)" and "in-situ interposition (SIP)" were used to construct a new polyamide layer with rigid–flexible microstructures. The fabricated SERS-0.50 membrane showed a 5-fold higher water flux and 2-fold increase in the Mg2+/Li+ separation factor compared with the IP membrane. Moreover, the SIP-0.15 membrane with an enhanced positive charge density exhibited a considerably higher Mg2+/Li+ separation factor (15.38, 500 % increase compared with that of the IP membrane) for brine with a Mg2+/Li+ ratio of 20. This study provides a reference for developing nanofiltration membranes used for high-efficiency Mg2+/Li+ separation. [ABSTRACT FROM AUTHOR]

Herein, plasticizer-assisted interfacial polymerization was developed to fabricate thin-film composite (TFC) reverse osmosis (RO) membranes with improved water permeability and comparable salt selectivity. Three representative phthalate acid esters, including dimethyl phthalate (DMP), dibutyl phthalate (DBP), and dioctyl phthalate (DOP), served as the plasticizer. FTIR results revealed that the introduction of plasticizers disrupted original amide-amide bonding between polyamide chains, converting polyamide structure from stiff to flexible, thus significantly promoting water diffusion efficiency through the polyamide matrix. Besides, the presence of plasticizers led to the creation of more voids in the polyamide layer, where water transport resistance was relatively low. Specifically, with the addition of 0.6 wt% DMP, water flux enhanced from 19.1 L m−2 h−1 of the virgin membrane to 72.5 L m−2 h−1, with NaCl rejection declining from 99.3% to 98.3%. And 0.6 wt% DBP-modified membrane showed water flux of 44.0 L m−2 h−1 and NaCl rejection of 98.9%. It was interesting to discover that DOP possessed the poorest plasticizing capacity, which contradicted the traditional cognition that DOP is one of the most resultful plasticizers for polymers. We believed it was the sizable alkyl moieties in DOP that suppressed the interaction between DOP molecules and polyamide chains. • Highly permeable RO membranes were prepared via plasticizer-assisted IP. • Three representative phthalate acid esters were used as the plasticizer. • Polyamide chain flexibility enhanced markedly in the presence of plasticizer. • Disruption of interchain bonding led to the enhancement of chain flexibility. [ABSTRACT FROM AUTHOR]