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An excellent positively charged nanofiltration (NF) membrane is of great significance for water softening. In this work, a novel positively charged composite PEI/TMA NF membrane was prepared by gradient cross-linking polyethyleneimine (PEI) with trimesic acid (TMA) on polyethersulfone ultrafiltration (PESU) membrane. The effects of concentration of PEI and TMA, the cross-linking reaction temperature and reaction time on membrane structure and performance were investigated in detail. The effects of PEI and TMA, reaction temperature and time on the membrane structure, composition and performance were investigated. The optimized preparation conditions of PEI/TMA NF membrane were fixed at 0.6% (m/v) PEI, 0.1% (m/v) TMA, 0.15% (m/v) SDS at 90 °C for 10 min. The as-prepared membrane exhibited a pure water flux of 19.1 L m−2 h−1 bar−1 and a rejection of MgCl2 93.0%, NaCl 38.2%, MgSO4 20.4%, and Na2SO4 8.8%. The functional layer is ultra-thin. Its high selectivity mainly results from Donnan effect. The long-term testing of our PEI/TMA NF membrane show a high stability. Compared with other positively charged membranes, the PEI/TMA NF membrane had unique advantages in the production process and a comprehensive performance.

Preparation of novel swelling resistance membrane by interpenetrating an immiscible flexible polyisobutylene (PIB) polymer into a rigid polyamide (PA) network by interfacial polymerization. Due to the force interlocking of flexible PIB, polyamide network has high strength and excellent resistance to methanol. The PA layer was characterized by mechanical strength, attenuated total reflection fourier transforms infrared spectroscopy (ATR-FTIR), small angle X-ray scattering (SAXS), contact angle, field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM). RO membrane performances were evaluated based on small molecule alcohol (methanol and ethanol) solution of Safranin O. The results show that the flexible PIB interpenetrates well in the rigid polyamide network and improves mechanical strength and swelling resistance. With an increasing concentration of PIB from 0% to 0.30% in the organic phase during the fabrication, the mechanical strength of the PA layer becomes 2.8 times that of the original, and the rejection of Safranin O increased from 95.43% to 99.43%, and the permeability coefficient (Bs) decreased from 5.22 to 0.47.

The enhancement in selectivity of nanofiltration (NF) membranes is of great significance for extending the application areas and improving the process economy, especially for the separation of monovalent/divalent ions. The characteristics of moderately increased pore size, fewer nonselective defects and a more uniform structure are conducive to NF membrane exhibiting higher rejection of divalent ions but lower rejection of monovalent ions. Nonylphenol polyoxyethylene ether (NP-10) was introduced in interfacial polymerization process in this study to optimize the microstructure and surface properties of polyamide (PA) layer to manufacture highly selective NF membranes. The hydrophobic benzene ring and aliphatic chain in NP-10 could form a local space that restricted the interfacial polymerization reaction on the side of the oil phase, thereby appropriately increasing the pore size of the PA layer. It was advantageous to the permeation of water molecules and monovalent ions with a smaller radius. The long hydrophilic oxyethylene group as a guide could facilitate the uniform diffusion of the monomer to the water/hexane interface. NP-10 as an amphiphilic substance would form a self-assembled network at the water/hexane interface, which was expected to optimize the distribution of aqueous amine monomers at the phase interface. Meanwhile, introducing NP-10 can form a stable interface and reduce the interface disturbance, thus inhibiting the formation of non-selective macropores (or “defects”) in PA layer, which could improve the separation selectivity of monovalent/divalent ions. In addition, the hydrophilicity and electronegativity were also enhanced. The results showed that the MWCO of NF membrane increased from 210.1 Da (TFC-0) to 269.6 Da (TFC-0.25), and the average pore radius increased from 0.248 nm to 0.276 nm. The water flux of optimized membrane was doubled compared to the control membrane. Most important, the optimized exhibited higher rejection of divalent Na2SO4 (from 98.07% to 99.43%), and meanwhile lower rejection of monovalent NaCl (from 54.07% to 27.52%). NaCl/Na2SO4 separation factor reached up to 130.53, which was about four times of TFC-0 membrane.

Thin film nanocomposite (TFN) membranes with improved permeability is important in the energy-efficient reverse osmosis membrane processes. In this paper, we demonstrate a facile method for the formation of polyamide/silica TFN membranes by an in-situ interfacial polymerization of aqueous amine and acid chloride/silicon tetrachloride (SiCl4) solutions. Water permeability is greatly enhanced with minimal loss in NaCl rejection. Polyamide/silica TFN membranes with 0.04% w/v SiCl4 exhibit a pure water permeability up to 9.7 L m−2 h−1 bar−1, which is 2.02 times more than that of the pristine thin film composite (TFC) membranes, while high rejection to NaCl (96.5%) is maintained. TEM tomograms confirm the existence of silica nanoparticles (NPs) in the thin PA film. More permeable voids are created in the cross-section of TFN membranes. Outer voids are buried underneath the PA protuberances and overhanging crumples. Inner voids and silica NPs are both encapsulated by polyamide. Top surfaces become more hydrophilic and negatively charged. With the optimal amount of SiCl4 loading, the formation of non-selective voids around the particles is minimized. Covalent and hydrogen bonds are formed between SiCl4 and PA polymers. These polyamide/silica nanocomposite membranes outperform many other TFN membranes in water permeability and salt rejection.

Novel high boron removal thin film composite (TFC) membranes with semi-interpenetrating networks were fabricated by interfacial polymerization (IP) with m-phenylenediamine (MPD) and 1,3,5-benzenetricarbonyl trichloride (TMC). The polyisobutylene (PIB) was added to the organic phase prior to IP. The membranes were characterized by attenuated total reflectance Fourier transform infrared spectrometry (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and the zeta potential and contact angle analysis. The results of this study demonstrate that the novel TFC membrane exhibited superior separation performance at a relatively low concentration of PIB (0.30%, m/v). As the concentration of the interpenetrating PIB in the membrane increased, the membrane morphology changed distinctly. Furthermore, the permeability coefficient of boron decreased from 20.84 to 3.26, and the rejection of boron increased from 81.36% to 93.12%.

Membrane separation has great potential for carbon dioxide capture, and materials play paramount important role in the membrane technology. In this paper, the mixed-monomer strategy is proposed for synthesis of a functional porous aromatic framework (PAF) named as PAF-45DPA. The monomer of diphenyl is employed for formation of the porous network and another monomer of diphenylamine is introduced to yield basic nitrogen sites. As a consequence, the prepared PAF-45DPA material possesses a surface area of 679 m2 g-1 with dominant pore size of ~0.58 nm which educes selective adsorption property toward carbon dioxide with IAST selectivity of 63.1 and CO2 uptake of ~45.3 cm3 g-1 at 298 K and 101 kPa measured from CO2 and N2 adsorptions. PAF-45DPA is subsequently used to fabricate hollow fiber membranes by hybridization with polysulfone (PSF) through the technique of dry jet-wet quench. Gas permeation analysis of CO2 and N2 reveals that the separation performance of PAF-45DPA/PSF is superior to those of PAF-45 and PDPA built from unary monomers. The PAF-45DPA/PSF membrane shows a dramatic improvement in the CO2/N2 separation factor (24.2) compared to PAF-45/PSF (15.4) and a significant enhancement in the CO2 permeance (72.6 GPU) compared to PDPA (51 GPU) at 298 K and 0.12 MPa. High stability of the PAF-45DPA/PSF membrane is also demonstrated together with its low cost and scale up production possibilities, which shed a light on advanced CO2 capture technology development for industrial gas exhausts.

The structure of the polyamide (PA) nanofilm formed via interfacial polymerization (IP) is vital to the permeance-selectivity of composite membranes. However, it is challenging to control the morphology (e.g., nodules, ridge-and-valley) of the PA nanofilm due to the fast IP kinetics. Herein, we deconstructed the kinetic pathways of IP to probe the structure of the PA nanofilm and demonstrated that (I) the main skeleton of the nanofilm was composed of sub-10 nm nanoclusters; (II) the growth and assembly of nanoclusters shaped the nanofilm structure. Furthermore, we controlled PA nanofilm structure via adjusting the monomers' stoichiometric ratio at the new reaction interface, and the resulted nodules with controlled size and surface characteristics endowed tunable water-salt transport properties. This work offered a detailed understanding of the formation and structure of IP PA nanofilm; these insights can potentially guide the production of high-performance polyamide-based thin-film composite membranes.

The separation of dyes and salts is very challenging in regards to treating high salinity textile wastewater. To effectively dispose dye/salt mixtures, it has become urgent to develop highly permeable and antifouling nanofiltration membranes. Herein, a novel loose nanofiltration membrane was fabricated by combining blending with interfacial polymerisation. Polyvinylidene fluoride (PVDF)/styrene-maleic anhydride (SMA) copolymer membranes with uniform microstructures were achieved via phase inversion by controlling the miscibility. Numerous carboxyl groups were gathered on the surface due to the amphiphilic SMA segregation during the membrane formation. Carboxylated carbon nanotubes (CNT-COOH) were used to further tune the membrane microstructures and promote the carboxyl groups segregation onto the surface. Ultimately, polyethylenimine (PEI) and triethanolamine (TEA) were co-deposited on the membrane surface by the amidation reaction and hydrogen bonding to form a loose structure. The optimized membrane exhibited high dye rejections to Congo red (99.9%), methyl blue (96.7%), acid fuchsin (96.1%), and low salt rejections to NaCl (1.7%), MgCl2 (4.5%), MgSO4 (1.2%). Significantly, it possessed a permeate flux of up to 251.6 L/m2·h·bar during the dye/salt mixtures filtration. Moreover, the optimized membrane also performed excellent antifouling properties toward proteins and dyes. Overall, this work provides a promising loose nanofiltration membrane for textile wastewater treatment.

Construction of high performance nanofiltration (NF) membrane is of critical importance in dye desalination. In this paper, a novel composite NF membrane with good dye/salt separation performance was prepared via blending and crosslinking method. Firstly, the membrane matrix was prepared by blending styrene-maleic anhydride (SMA) with polyether sulfone (PES) via non-solvent induced phase separation (NIPS), then polyethylenimine (PEI) was introduced on the membrane surface by crosslinking reaction with SMA. Single component filtration tests of the prepared NF membrane showed that the rejection of the dye with the molecular weight greater than 696 Da reached more than 99% and the membrane possessed high flux of above 23 L/m2 h bar. The separation tests of Congo red and NaCl mixed solution at optimized conditions exhibited 99.4% rejection for Congo, and 2.5% rejection for NaCl, moreover, the separation performance remained stable in the test run for 36 h. All these indicate that the prepared NF membrane can be applied to dye desalination.

The removal of small and neutral boron molecules from seawater remains a critical challenge in energy-saving and low-cost desalination. In this paper, a high boron removal reverse osmosis (RO) membrane was designed by embedding sulfonyl moleculars in the polyamide (PA) network. The swelling PA structure has enlarged free volumes. It would induce more facile penetration of 4-nitrobenzenesulfonyl chloride (NBS). Evaporation of solvent molecules contracts the PA network and leads to the fixation of the NBS molecules into the PA network. The swelling of the polyamide network was studied systematically. The most suitable swelling solvent was selected based on the solubility parameter and the restoration capability. The “swelling-embedding-shrinking (SES)” strategy reconstruct the free volume of PA chains. It resulted in significantly higher rejection of neutral boron molecules due to enhanced steric hindrance by embedded NBS plugs and synergistic exclusion effect by –SO3H groups. Meanwhile, the alteration of membrane composition and structure were kept minimal. Further, the impacts of key determining factors (polarity, steric hindrance, and affinity) on boron separation performance were systematically analyzed by boron-containing compounds with different numbers of hydrogen bonding sites (or dipole moments) or molecular volumes. Under simulated seawater conditions, the boron rejection of the SES modified reverse osmosis membranes increased from 82.12% to 93.10%, and the salt rejection rate increased to 99.57%. Our study shows that the swelling induced embedding of NBS molecules can be readily adopted to regulate the permselectivity of the PA layer towards removal of boron species.

PVDF/PMMA blend microporous membranes were fabricated via thermally induced phase separation (TIPS) process using a single diluent. Then the blend membranes were soaked in a liquid electrolyte to form polymer electrolytes. Finally, the polymer electrolytes were assembled in coin cells to test electrochemical properties. The effects of PMMA/PVDF weight ratio on the phase diagram of PVDF/PMMA/diluent system, morphology, crystallinity, crystal structure, mechanical properties and porosity of the membranes were discussed. The electrochemical properties of corresponding polymer electrolytes, such as ionic conductivity, cell charge–discharge capacity and discharge performance at different current densities, electrochemical stability windows, were also investigated in this paper. It was found that the cloud point of the system decreased and the membrane morphology changed from cellular structure to network structure with an increase in the amount of PMMA. Both electrolyte uptake of blend membranes and ionic conductivity of corresponding polymer electrolytes also increased with an increase in the amount of PMMA. The maximum ionic conductivity was found to reach 3.38×10 −3 S/cm at 25 °C. The graphite/polymer electrolyte/LiFePO 4 cells of blend membranes showed higher charge–discharge capacity and better discharge performance at different current densities. Electrochemical stability window was stable up to 4.7 V (vs. Li + /Li).