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According to the Freeman theory, increasing the backbone stiffness to some extent is an effective way to obtain the remarkable membrane with both high permeability and selectivity. In this work, a high performance nanofiltration (NF) membrane was prepared via tailoring the polyester/polyamide backbone stiffness. The flexible monomer-piperazine (PIP) and the rigid monomer-bisphenol F (BPF) were selected as the aqueous phase monomers, and they were interfacial reacted with trimesoyl chloride (TMC) on the polyethersulfone (PES) UF membrane to generate the polyester/polyamide layer. By mixing PIP with BPF, both of the polyester/polyamide backbone stiffness and microporosity degree enhanced. As a result, the PIP/BPF NF membrane possessed a 2.6-fold pure water flux (PWF) of the PIP NF membrane (the salt rejection remained at the same level), and 4.8-fold PWF of the BPF NF membrane. Our results revealed a novel and facile way to improve the NF membrane performance. [ABSTRACT FROM AUTHOR]

A novel polypiperazine-amide nanofiltration (NF) membrane with very high salt rejection was successfully developed in this work. The NF membrane chlorine-tolerant ability were improved greatly after mixing a small amount of α,ω-diamino poly(ethylene glycol) (NH 2 -PEG-NH 2 ) with piperazine (PIP) in the aqueous phase. The XPS result demonstrated that the polymerization degree of the NF membrane was notably enhanced with the addition of NH 2 -PEG-NH 2 . The solute rejections and chlorine tolerance were improved remarkably, while the permeate flux remained almost at the same level. When the NH 2 -PEG-NH 2 (2 kDa) content in the total amine was 1%w/w (0.01%w/v in the aqueous solution), NF membrane performance was optimal. This membrane exhibited a pure water flux (PWF) of 34.9 L m −2 h −1 along with Na 2 SO 4 , MgSO 4 , MgCl 2 and NaCl rejections of 99.5%, 99.2%, 90.9% and 58.3% (2000 ppm, 6 bar, 25 °C), respectively. Moreover, the NF membrane performance was maintained after being treated by 14,000 ppm NaClO for 1 h. Therefore, adding a small amount of NH 2 -PEG-NH 2 in the aqueous phase could be considered to be an effective way to improve the polypiperazine-amide NF membrane chlorine-tolerant ability. [ABSTRACT FROM AUTHOR]

Novel high-flux thin film composite (TFC) nanofiltration (NF) membranes were fabricated by the sodium hypochlorite (NaClO) pre-oxidation of the mixed diamine monomers of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) in the aqueous phase solution, and via interfacial polymerization (IP) with trimesoyl chloride (TMC) on the polysulfone (PSF) ultrafiltration (UF) membrane. The chemical change of the pre-oxidation aqueous phase solution was characterized by LC-MS. By optimizing the NaClO and NaOH content in the aqueous phase solution, the pure water flux was improved greatly and the salt rejection kept on a high level (>90%). The properties of NF membranes were characterized by XPS, SEM, AFM and contact angle. Through the NaClO pre-oxidation of the mixed diamine monomers of PIP and BHTTM in the aqueous phase solution, the active layer of NF membrane became thinner and the pore size of NF membrane was enlarged. Besides, after oxidation treatment by 3000 ppm active chlorine solution for 1 h, the NF membrane exhibited pure water flux (PWF) with 161 (LMH) and Na 2 SO 4 rejection of 92.1% under 0.6 MPa. The molecular weight cut-off (MWCO) of the NF membrane was greater than 500, which was calculated from the carbohydrates rejection. The good performance and the satisfactory stability of the novel high-flux NF membrane demonstrated its good potential in the practical application. [ABSTRACT FROM AUTHOR]

Using Polysulfone (PSF) ultrafiltration (UF) membrane as porous support, a chlorine-tolerant nanofiltration (NF) membrane was prepared by interfacial polymerization of piperazine (PIP) and 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4'-methylenedianiline (BHTTM) mixture with trimesoyl chloride (TMC). The XPS, SEM, AFM and contact angle methods were employed to characterize the physicochemical properties and morphology of the prepared NF membranes. The effects of preparation conditions such as reaction time, monomers mixing ratio and oxidation treatment on NF membrane performance were investigated. The salt rejection of the NF membrane met the order of Na 2 SO 4 >MgSO 4 >NaCl, indicating the membrane possessed a negative surface charge. The results showed the NF membrane prepared under the optimum conditions exhibited pure water flux (PWF) with 79.1 (L/m 2 h) and Na 2 SO 4 rejection of 99.5% under 0.6 MPa. The optimized post oxidation condition was treated by 3000 ppm NaClO solution for 1 h. The best NF membrane had a molecular weight cut-off (MWCO) less than 300 Da, corresponding to the pore size of 1 nm, which was calculated from the rejection of carbohydrates. The robustness of the NF membrane was proven by showing satisfactory stability in the long time running. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the temperature and time of the heat curing process have important effects on the nanofiltration (NF) membrane structure and properties. However, the mechanism of the relative humidity (RH), as one of the important factors in the heat curing of NF membranes, is still unclear. To analyze the specific effect of RH, we compared the heat curing results of the NF polyamide (PA) membranes fabricated with different monomer concentrations at various RH. The nanofiltration performance of the membranes appeared to be non-uniform when the RH was in the range of 40 %–60 %. Within the appropriate RH range, the rejection of Na 2 SO 4 was preserved at about 98.5 % for the manufactured NF membranes. At high concentrations, the increasing RH created a discontinuous condensate layer on the PA layer surface, which affected the morphology and physicochemical properties of the NF membrane causing a doubling of pure water permeability (PWP) to 8.33 L m−2 h−1·bar−1. At low concentrations, the PA layer was not significantly changed with the increase of RH, but the evaporation of water from the smaller capillary pores in its PES substrate was slowed down, which reduced the capillary stress on the substrate and prevented the collapse of the substrate pore size, resulting in a nearly 20 times increase in its PWP to 39.7 L m−2 h−1·bar−1. This work reveals the effect of RH during heat curing and gives significant guidance to the design and synthesis of high-performance NF membranes. [Display omitted] • The effect of relative humidity during heat curing on TFC nanofiltration membranes was investigated. • Capillary stress was introduced to reveal the mechanism of nanofiltration membranes flux variation. • The surface morphology of nanofiltration membranes changed with the relative humidity. • The relative humidity affects the nanofiltration membrane uniformity. [ABSTRACT FROM AUTHOR]

By causing the water molecule vibration to generate heat, microwave has become a rapid and efficient heating method which is widely used in industrial production. Herein, microwave heating assistant interfacial polymerization (IP) process was innovatively applied to fabricate polypiperazine-amide nanofiltration (NF) membrane for the first time. With microwave heating, a uniform and faultless polyamide (PA) layer could be generated with low monomer concentration. The pure water flux (PWF) of the NF membrane fabricated with microwave heating was 157.1 L m-2 h-1 with the Na 2 SO 4 rejection of 97.7% under 0.6 MPa. Meanwhile, such NF membrane showed extraordinary selectivity to Cl- and SO 4 2− for a series of mixing solution with different concentrations. This new insight into microwave heating assistant IP provides a feasible method for the high-permselectivity NF membranes fabrication. Image 1 • The microwave heating was applied for the IP process to fabricate TFC NF membrane for the first time. • The uniform and faultless PA layer could be generated with low monomer concentration with microwave heating. • The NF membrane showed good permeability and rejection and high selectivity to Cl- and SO 4 2−. [ABSTRACT FROM AUTHOR]

• A novel TFC NF membrane was fabricated by incorporation of β-CD into polyamide backbone. • The effect of β-CD on the NF membrane performance was studied thoroughly. • Such NF membrane showed a high permselectivity performance. Based on the Freeman theory, tailoring polymer backbone stiffness can improve membrane performance. Therefore, a rigid monomer—bisphenol F—to enhance the backbone stiffness of polyester/polyamide was utilized to prepare high performance nanofiltration (NF) membranes in the previous work. Here, the three-dimensional (3D) hollow-bowl-structure monomer—beta cyclodextrin (β-CD)—is added into the polyester/polyamide backbone to fabricate a 3D-microstructure NF membrane. With the incorporation of β-CD, the pure water flux (PWF) increases by 68% (up to 152 L m−2 h−1, 0.6 MPa), while the rejection of Na 2 SO 4 remains high (96.8%). Surprisingly, such NF membrane exhibits a very low rejection of NaCl (1.1%) and high rejection of Na 2 SO 4 (up to 95.8%) when dealing with a Na 2 SO 4 /NaCl mixed solution. The fabricated 3D-microstructure NF membrane shows the potential to be applied in the monovalent/divalent anion separation field. [ABSTRACT FROM AUTHOR]

A novel chitosan (CS)-piperazine (PIP) composite nanofiltration (NF) membrane with satisfied characteristics for brackish water and seawater desalination was successfully developed. PIP was mixed with CS during the interfacial polymerization (IP) process to enhance the NF membrane permeate flux. The resultant NF membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), contact angle. Effects of CS concentration, trimesoyl chloride (TMC) concentration, reaction time and the mixing ratio of CS/PIP on NF membrane performance were investigated thoroughly. When PIP in the aqueous phase monomers reached to 25% (w/w), the PWF (60.6 L·m−2·h−1) was synergistically improved by nearly 2 times without a significant reduction of Na2SO4 rejection (89.1%). Moreover, the NF membranes possessed excellent performance for the desalination of brackish water and seawater, which showed high potential to be applied in the desalination process for water treatment. [ABSTRACT FROM AUTHOR]

Monomers are elementary units that constitute the polyamide layer, which determines the properties of nanofiltration membranes. The design of nanofiltration membranes with both high separation performance and outstanding chemical stability remains a challenge. In this study, two typical monomers, heterocyclic monomer molecule-piperazine (PIP) and carbon ring molecule-1,4-cyclohexane diamine (CHDA), were applied as aqueous monomers for interfacial polymerization to generate polyamide nanofiltration membranes. The physicochemical properties of the two nanofiltration membranes were comprehensively investigated. The results demonstrated that the nanofiltration membrane fabricated via CHDA exhibited more chemical stability than that fabricated via PIP. The mechanisms influencing the chemical stability difference were elucidated via multiscale simulation. The CHDA polyamide has higher levels of HOMO-LUMO energy and Gibbs-free energy, which make it more stable under harsh chemical environments. Overall, this work presents the effect of the diamine structure on the chemical stability of polyamide NF membranes, which can inspire highly chemically stable nanofiltration membrane fabrication. [Display omitted] • Effect of diamine structure for NF membrane chemical stability was investigated. • Carbon ring molecule had better chemical stability than heterocyclic molecule. • Experimental study showed a high correlation with simulation calculations. [ABSTRACT FROM AUTHOR]

Currently, most nanofiltration membranes exhibit satisfactory separation performance on the anions or cations, and few membranes could concurrently separate anion and cation. Therefore, preparing nanofiltration membranes with excellent separation performance for both anionic and cationic ions remains a challenge. Herein, we have developed a series of nanofiltration membranes using conventional interfacial polymerization with different ratios of trimesoyl chloride (TMC) and piperazine (PIP) concentrations. In the interface polymerization process, the amine groups carried by PIP imparted a positive charge, while the hydrolysis of acyl chloride groups resulted in the generation of carboxylic acid groups that introduced a negative charge. The mix-charged nanofiltration membrane could be fabricated by varying PIP/TMC concentration ratios. The optimized membrane exhibited high rejection rates for bivalent ions (Na 2 SO 4 rejection of 96.6 %, MgCl 2 rejection of 93.0 %), and its selectivity for Mg2+/Li+ mixed solution was improved significantly. This work provides a novel approach for the development of nanofiltration membranes capable of effectively separating mono-/divalent ions. [Display omitted] • Fabrication of mixed-charged polyamide membranes via regulating the PIP/TMC ratio directly. • High PIP/TMC ratio leads more unreacted amine groups in the polyamide which was beneficial to MgCl 2 rejection. • Such NF membrane showed excellent separation efficiency to Mg2+/Li+ and SO 4 2−/Cl−. [ABSTRACT FROM AUTHOR]

This work describes a novel nanofiltration membrane fabrication strategy in which the octadecylamine-grafted GO with the organophilic property is incorporated in organic phase during interfacial polymerization (IP) in order to protect the polyamide backbone from the attack of free chlorine. Meanwhile, the aqueous phase containing mixed amines of piperazine (PIP) and the fluorine-containing monomer (2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline, BHTTM) enables further improvement in chlorine resistance of the thin film nanocomposite (TFN) membrane. The modified GO was systematically characterized by TEM, FT-IR, TGA and XRD. And the membrane properties were investigated by XPS, TEM, AFM and dynamic contact angle. The octadecylamine-grafted GO TFN membrane (TFNMA-GO-ODA) exhibits measurably smoother and less hydrophilic surface compared to TFC membrane with mixed amines as well as the similarly fabricated GO TFN membrane. The TFNMA-GO-ODA demonstrated a pure water flux of 49.6 L m −2 h −1 (0.6 MPa), which was nearly 2.5 times than that of pristine PIP TFC membrane and 1.6 times than that of mixed-amine TFC membrane, while keeping high Na 2 SO 4 rejection of 98.4%. More importantly, the TFNMA-GO-ODA presented excellent chlorine resistance, benefiting from the existence of fluorine-containing groups in BHTTM and the protective effect of stable graphene nanosheets. The results indicate great potential of such membrane in water desalination and purification in industrial scale. [ABSTRACT FROM AUTHOR]

Thin film composite (TFC) hollow fiber nanofiltration (NF) membranes were fabricated via interfacial polymerization, with mixed diamines of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) as water phase and trimesoyl chloride (TMC) as organic phase. Fabricated membranes were characterized for ATR-FTIR, SEM, AFM, and water contact angle. Formation conditions of the selective polyamide layer have been optimized for a good NF membrane performance. The pure water flux of NF membrane prepared under optimized conditions was 31.2 L·m − 2 ·h − 1 and the rejection for Na 2 SO 4 was 99.7% at 6 bar. The rejections of NF membranes for different salts followed the order: Na 2 SO 4 > MgSO 4 > NaCl > MgCl 2 . The molecular weight cut-off of NF membrane was around 300 Da. The performance of NF membranes was stable during a 7-day filtration process for rejecting different species ions including heavy metal ferric ion (FeCl 3 and Fe 2 (SO 4 ) 3 ) and oxyanions (SO 4 2 − and HPO 4 2 − ), in addition to different inorganic salts. Also, the NF membranes exhibited chlorine tolerant property. This work demonstrates the potential of PES outer-selective TFC hollow fiber membranes for desalination or water softening process, provides database to fabricate suitable NF membranes for long-term salts removal and raise a simple technique to form a thin chlorine-tolerant polyamide layer. [ABSTRACT FROM AUTHOR]