Polypiperazine-amide Nanofiltration Membrane Research Articles

How to understand the effect of relative humidity on the morphology and performance of polypiperazine-amide NF membrane during heat curing process

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 Na2SO4 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.

Novel Insight on the Effect of the Monomer Concentration on the Polypiperazine-Amide Nanofiltration Membrane

Novel Insight on the Effect of the Monomer Concentration on the Polypiperazine-Amide Nanofiltration Membrane

Microwave heating assistant preparation of high permselectivity polypiperazine-amide nanofiltration membrane during the interfacial polymerization process with low monomer concentration

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 Na2SO4 rejection of 97.7% under 0.6 MPa. Meanwhile, such NF membrane showed extraordinary selectivity to Cl- and SO42− 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.

How to understand the effects of heat curing conditions on the morphology and performance of polypiperazine-amide NF membrane

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na2SO4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane.

Effect of varying piperazine concentration and post-modification on prepared nanofiltration membranes in selectively rejecting organic micropollutants and salts

Nanofiltration (NF) is considered as a promising technology for the removal of trace organic compounds (TrOCs) for wastewater reclamation, while a simultaneous low rejection of salts is desirable for the ease of using the reclaimed water. This study was conducted to exploit the potential of polypiperazine-amide NF membranes in achieving selective separation of TrOCs and NaCl by varying the concentration of the diamine monomer, piperazine (PIP), for interfacial polymerization and by modifying the nascent membrane surface with hydrophilic monomers, diethanolamine (DEA) and monoethanolamine (MEA). Results showed that increasing PIP concentration could decrease the membrane pore size and reduce the surface negative charge density, which led to an increased rejection of xylose and a reduced rejection of NaCl. The grafting of DEA or MEA molecules could further decrease the NaCl rejection, substantially improve the water permeability and maintain an effective removal for eight pharmaceuticals (PhACs). The optimal membrane prepared with a PIP concentration of 2.0 wt% and subsequently modified by MEA exhibited a rejection of NaCl at 33.1% and an average rejection of PhACs at 90.8% in a 10 mmol/L NaCl solution under an applied pressure of 6 bar. The membrane could have an even higher selectivity when the NaCl concentration was increased to higher levels. These results demonstrated the feasibility and versatility of the membrane in separating TrOCs from NaCl for wastewater reclamation.

Understanding the chlorination mechanism and the chlorine-induced separation performance evolution of polypiperazine-amide nanofiltration membrane

Although the tertiary amide bonds are quite stable to oxidants, the typical polypiperazine-amide (PPA) nanofiltration membranes (NFMs) were still reported to be susceptible to chlorine degradation. However, the understanding of the chlorination mechanism and the chlorine-induced separation performance evolution of the PPA NFMs still remains incomplete, significantly limiting the development of chlorine-resistant NFMs. In this work, two types of self-made PPA NFMs with different physicochemical structures and separation performance were employed to investigate the chlorination processes. The regeneration behaviour of the chlorinated PPA NFMs was studied for the first time. Our results indicated that the deterioration of the PPA separating layer upon chlorine exposure follows two pathways: reversible chlorine substitution of the -NH group to -NCl group, and oxidation of the -NH group to imine group. Part of the -NCl groups could be reduced to -NH groups during the regeneration process. No cleavage of tertiary amide bonds in the PPA polymer occurred. Separation performance evolution of the PPA NFMs after chlorination or regeneration was mainly induced by the variation of -NH group content in the PPA separating layer. The loss of -NH groups after chlorination and the reformation of -NH groups after regeneration could not only affect the density of the PPA separating layer through hydrogen bonds but also the electrostatic interaction between the PPA separating layer and ions. Additionally, the regenerated PPA NFMs showed good stability under elevated pressure or continuous filtration.

Improving the chlorine-tolerant ability of polypiperazine-amide nanofiltration membrane by adding NH2-PEG-NH2 in the aqueous phase

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) (NH2-PEG-NH2) 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 NH2-PEG-NH2. The solute rejections and chlorine tolerance were improved remarkably, while the permeate flux remained almost at the same level. When the NH2-PEG-NH2 (2kDa) 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 34.9Lm−2h−1 along with Na2SO4, MgSO4, MgCl2 and NaCl rejections of 99.5%, 99.2%, 90.9% and 58.3% (2000ppm, 6bar, 25°C), respectively. Moreover, the NF membrane performance was maintained after being treated by 14,000ppm NaClO for 1h. Therefore, adding a small amount of NH2-PEG-NH2 in the aqueous phase could be considered to be an effective way to improve the polypiperazine-amide NF membrane chlorine-tolerant ability.

Polypiperazine-amide Nanofiltration Membrane Modified by Different Functionalized Multiwalled Carbon Nanotubes (MWCNTs).

In this work, three modified multiwalled carbon nanotubes (MWCNTs) with carboxyl (MWCNT-COOH), hydroxyl (MWCNT-OH) and amino groups (MWCNT-NH), respectively, were added into the aqueous phase containing piperazine (PIP) to fabricate the nanocomposite nanofiltration (NF) membranes via interfacial polymerization. The influences of functional groups of MWCNTs on the performance of modified NF membrane were investigated. The MWCNTs were characterized by TEM, FT-IR and TGA; meanwhile, the properties of the membranes were evaluated by XPS, TEM, AFM and contact angle. The XPS results proved the successful incorporation of MWCNT in the active layer of modified NF membrane. When the MWCNT concentration is 0.01% (w/v), all the nanocomposite membranes possessed the optimal separation properties, among which the membrane incorporated with MWCNT-OH demonstrated the highest water flux of 41.4 L·m(-2)·h(-1) and the Na2SO4 rejection of 97.6% whereas the one with MWCNT-COOH had the relative lowest rejection of 96.6%. Furthermore, the increased hydrophilicity of functional groups in modified MWCNTs resulted in different nodular surface morphologies, thicknesses and hydrophilicities of the nanocomposite membranes. All the membranes possessed a molecular weight cutoff (MWCO) within 300 Da and good operation stability.

Graphene oxide polypiperazine-amide nanofiltration membrane for improving flux and anti-fouling in water purification

In this study, a facile polypiperazine-amide (PPA) composite nanofiltration (NF) membrane with nanomaterial graphene oxide (GO) incorporated into a polyamide (PA) layer for high water flux and anti-fouling was fabricated by interfacial polymerization (IP). The chemical composition, structure and surface properties of the fabricated PPA/GO and PPA composite NF membranes were characterized by FTIR, XPS, FE-SEM, AFM, zeta-potential and contact angle measurements. The separation properties and anti-fouling ability of the PPA/GO NF membrane were investigated and discussed. The experimental results indicated that the water flux of the PPA/GO (300 mg L−1 GO) membrane increased from 66 (L m−2 h−1) to 87.6 (L m−2 h−1) under the operating pressure of 0.6 MPa, almost 1.4 times that of the PPA (without GO) membrane. However, the high salt rejection was still retained in the order of Na2SO4 (98.2%) > MgSO4 (96.5%) > NaCl (56.8%) > MgCl2 (50.5%). An anti-fouling test revealed that the PPA/GO membrane had excellent anti-fouling properties due to the enhanced hydrophilicity and decreased roughness induced by the GO nanosheets. Thus, the PPA/GO membrane can be efficiently and endurably applied in water purification.

Polypiperazine-amide nanofiltration membrane incorporated with poly(ethylene glycol) derivative for electrodialysis concentrate treatment

Abstract We report a facile approach to prepare antifouling nanofiltration (NF) membrane to treat electrodialysis (ED) concentrate which contained anionic polyacrylamide (APAM). The NF membrane was fabricated through trimesoyl chloride (TMC) reacting with the hydrophilic poly(ethylene glycol) (PEG) derivative (i.e. Jeffamine) in piperazine (PIP) aqueous solution by means of interfacial polymerization (IP). The membrane surface characterization, performance of permeation flux and antifouling property were throughly investigated in this paper. The presence of Jeffamine in the polyamide matrix was verified by the Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The salts and APAM rejection was raised up and the permeation flux decline was slowed down for the ED concentrate treatment, which indicated that the antifouling performance was improved through adding Jeffamine. The optimized Jeffamine addition amount was 15 wt% (in the piperazine solution) at which the largest pure water flux enhancement and the best antifouling performance were achieved. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the polypiperazine-amide NF membrane exhibited that the surface smoothness was improved. Accordingly, it could be concluded that the addition of Jeffamine improved the NF membrane hydrophilicity and surface smoothness which could lead to the permeation flux enhancement and the antifouling property improvement.

Poly(styrene sulfonic acid) sodium modified nanofiltration membranes with improved permeability for the softening of highly concentrated seawater

Poly(styrene sulfonic acid) sodium salt (PSSS)/polypiperazine-amide nanofiltration (NF) membrane and PSSS/SiO2/polypiperazine-amide NF membrane were prepared by interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on polyethersulfone (PES) supporting membrane. Effect of PSSS and silica concentrations were discussed. The active surface of the membrane was characterized by using SEM and AFM. The results showed that PSSS/polypiperazine-amide NF membrane prepared under the optimum conditions exhibited Na2SO4 rejection of 96.1% and water flux with 55.7Lm−2h−1 at operation pressure of 0.6MPa. The rejection of Na2SO4, MgSO4, MgCl2 and NaCl follows a decreasing in order of 96.1%, 85.2% 45.4% and 21.1% respectively. After addition of 0.2% (w/v) silica in the aqueous phase, the water flux increased 42.7% compared with only polypiperazine-amide NF membrane. The PSSS/polypiperazine-amide NF membrane shows a promising capability for softening highly concentrated seawater from 8–20wt.%.

Polypiperazine-amide nanofiltration membrane containing silica nanoparticles prepared by interfacial polymerization

Silica/polypiperazine-amide nanofiltration (NF) membranes were prepared by interfacial polymerization on polyethersulfone (PES) supporting membrane. Different preparation conditions and NF membrane performances were discussed, including silica concentrations, monomer concentrations, reaction time and salt rejections. The chemical structure characterizations of polyamide composite membrane were carried out by attenuated total reflectance infrared (ATR-IR). The surface images and cross sections were observed by scanning electron microscope (SEM) and atomic force microscopy (AFM). The results showed that polypiperazine-amide NF membrane prepared under the optimum conditions exhibited Na2SO4 rejection of 97.4% and water flux of 46.8l.m−2.h−1. After addition of silica sol in the aqueous phase, the rejection of the resulting membrane changed slightly, but the water flux increased 21.1% than polypiperazine-amide NF membrane. According to the rejection of polyethylene glycols (PEGs), the molecular weight cut-off (MWCO) of the resulting membrane was under 600Da.