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Abstract A polyvinyl chloride (PVC)-based positively-charged nanofiltration membrane was fabricated from polyvinyl chloride- graft -poly(N,N -dimethylaminoethyl methacrylate) by heating and crosslinking treatment. We characterized the surface chemical compositions, membranes structures, surface hydrophilicity and surface charges of the prepared membrane. The estimated membrane pore diameter is 1.98 nm and the pore diameters are in the range of 0.5–2.0 nm. The membrane exhibits excellent water permeability (9.3 L m−2 h−1 bar−1) and salt rejection (93.1% with MgCl 2 solution). Both the heating treatment and crosslinking reaction can diminish the pore size of the precursor membrane. The membrane hydrophilicity is improved after quaternization, leading to higher water permeability compared with the membrane treated by heating only. Moreover, surface quaternization and crosslinking offer the membrane excellent pressure resistance and long-term stability. The prepared nanofiltration membrane has great promise in many applications including water softening and multivalent ion removal. Highlights • Positively charged nanofiltration membrane was directly fabricated from polyvinyl chloride copolymer. • The membrane was formed after the heating treatment and crosslinking reaction. • The membrane exhibited 9.3 L m−2 h−1 bar−1 of water permeability and 93.1% of MgCl 2 rejection. • The membrane had excellent pressure resistance and long-term stability. [ABSTRACT FROM AUTHOR]

Abstract Different from the typical interfacial polymerization for nanofiltration membrane fabrication, we proposed a novel method to prepare charged nanofiltration membrane via rapid immersion thermal annealing process with the ultrafiltration membrane, which was prepared from the amphiphilic copolymer, poly(vinyl chloride) -g- poly(2-(dimethylamino)ethyl methacrylate) (PVC -g- PDMA) via non-solvent induced phase separation. The pore structures and chemical properties of the membranes, and annealing conditions including the media where the membrane was annealed, annealing temperature and time, were investigated in detail. It is found that the porous separation layer was collapsed to be a stable, defect-free, and smooth film as the dense separation layer of nanofiltration membrane when it was annealed in n -heptane above its glass transition temperature (T g) for only 1 min while the pore size cutoff was tailored from 20 nm to 2 nm. Salt rejections were in the order of MgCl 2 > NaCl > MgSO 4 > Na 2 SO 4 at neutral condition due to Donnan repulsion, indicating a typical positively charged nanofiltration membrane. Overall, this rapid immersion thermal annealing process provides a facile and effective strategy to tailor ultrafiltration membrane toward nanofiltration applications for amphiphilic copolymer based membranes. Graphical abstract fx1 Highlights • NF membrane was formed rapidly via thermal annealing from ultrafiltration membrane. • Pore size of NF membrane could be tailored by the annealing condition. • The positively charged NF membranes showed high divalent cations rejection and water permeace. • Outstanding adhesive strength between the supports and the separation layer was attained. [ABSTRACT FROM AUTHOR]

A metal-organic composite membrane with sub-2 nm pores was developed via interfacial coordination reaction in biphasic systems for the first time. Herein, tannic acid (TA) was dissolved in water, as aqueous phase; iron(III) acetylacetonate (Fe(acac) 3), used as Fe(III) source, was dissolved in n -hexane as organic phase. A detailed study was conducted to obtain the defect-free TA-Fe(III) separation layer, including the salt concentration in aqueous solution, pH of the aqueous solution and the ratio of TA to Fe(acac) 3. The results indicated that the defect-free TA-Fe(III) composite membrane formed when the tris-complex (TA 3 -Fe(III)) was achieved. The optimal condition for preparing TA-Fe(III) composite membrane was using aqueous solution containing 0.4 M NaCl at pH = 6 with the ratio of TA to Fe(acac) 3 of 10. Different from the typical separation layer formed on the membrane surface by interfacial polymerization, the TA-Fe(III) separation layer was formed in the pores of the substrate, which is attributed to the higher diffusion coefficient of Fe(acac) 3 from organic phase to aqueous phase. This work provided a novel strategy to fabricate metal-organic composite membrane with sub-2 nm pores; meanwhile, the new-prepared membrane shows a high Na 2 SO 4 rejection of 97.3% with the water permeance of 8.6 L m−2 h−1 bar−1, and a high VB 12 rejection of 97.6%, indicating an excellent ion/molecule separation performance. Image 1 • TA-Fe(III) composite membrane with sub-2 nm pores was fabricated via interfacial coordination reaction for the first time. • Defect-free TA-Fe(III) composite membrane formed when the tris-complex (TA 3 -Fe(III)) was achieved. • Separation layer is formed in the pores of the substrate. • The membrane exhibited 8.6 L m−2 h−1 bar−1 of water permeance and 97.3% of Na 2 SO 4 rejection. [ABSTRACT FROM AUTHOR]

Positively-charged nanofiltration (NF) membranes have attracted more attention compared with traditional negative NF membranes. In this work, one-step self-assembly strategy was designed to prepare positively-charged NF separation layer by the close packing of poly(styrene- r -quaternized 2-(dimethylamino)ethyl methacrylate) (P(St- r -QDMA)) nanoparticles (NPs) with intramolecular crosslinking structure. Meanwhile, the pore size of NF membrane was tailored by regulating the aggregation of the NPs using different ions and annealing conditions. Herein, water was used as a dispersant to obtain P(St- r -QDMA) NPs dispersion, which is non-toxic and green. The pore size cut-off (PSCO) of the separation layer is well controlled in the range of 0.98–4.04 nm. The optimal membrane showed molecular weight cut-off (MWCO) of 380 Da (i.e., PSCO, 0.98 nm) with the isoelectric point of 9.4, which effectively improved the separation performance for divalent cations (97.2 % for MgCl 2 and 96.0 % for CaCl 2) and neutral small molecules (97.7 % for VB 12 and 92.5 % for PEG400). This work gives a novel and convenient method to construct positively-charged NF membrane with controlled pore sizes, which will be a promising candidate for water softening and molecular separation. [Display omitted] • Positively-charged nanofiltration membrane was prepared by nanoparticles assembly. • The pore size of membrane was tailored by ion concentration and annealing temperature. • It is a novel and convenient preparation method. • The membrane is promising in water softening and molecular separation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel binary organic phosphonic acid was firstly integrated into nanofiltration membrane. • The rejection of membrane incorporated with AA was improved, while the permeability exhibited no decline. • Mono-/divalent anion selective separation factor surpass 500 even in high saline solution up to 20 g/L. • The membrane exhibit excellent chlorine resistance and anti-fouling performance. Nanofiltration membrane (NF) have become increasingly crucial in ion separation. However, traditional polyamide (PA) NF suffers from poor selectivity for mono-/divalent anions due to weak charges and structure defects. Thus, a novel binary organic phosphonic acid, alendronic acid (AA), was firstly used as an aqueous co-monomer via interfacial polymerization (IP) to create negatively charged nanofiltration membranes with both higher charge density and pore size homogeneity for the separation of mono-/divalent anions. Both structure characterization and performance tests demonstrated the successful introduction of AA in the separation layer. Compared with pristine membrane, the NaCl/Na 2 SO 4 selectivity of membrane incorporated with AA was four times improved, while the permeability exhibited no decline. Simultaneously, the separation efficiency of Cl-/SO 4 2- was tested in NaCl/Na 2 SO 4 binary mixed solutions with varying total concentrations and different mass ratios, and the separation factor consistently exceeded 500 across a concentration range of 1 g/L to 20 g/L. Moreover, the AA-integrated membrane exhibited excellent chlorine resistance after 20000 ppm·h of chlorine treatment, which is promising for high efficiency separation of mono-/divalent anions in industrial applications. [ABSTRACT FROM AUTHOR]

To enhance hexavalent chromium (Cr(VI)) removal performance under acidic conditions, the nanofiltration (NF) membrane with enhanced negative charge was fabricated via introducing 2, 5-diaminobenzenesulfonic acid (DABSA) into polyamide layer. The control membrane (NF-P) was directly prepared from piperazine and 1, 3, 5-benzenetricarbonyltrichloride. Surface chemical compositions, morphology, surface charge, pore size, permeability and pH-dependent separation performance of the fabricated membranes were characterized. The membranes showed the similar water permeance (∼11.5 L m-2 h−1 bar−1) and Na 2 SO 4 rejections (∼98%) under neutral environments. The DABSA introduced NF membrane (NF-PD) was negatively charged in the pH range of 2.5–11, while the isoelectric point for NF-P was ∼pH 4.0. Cr(VI) removal ability was then evaluated under various concentrations and pH environments. The results indicated that NF-PD showed the better Cr(VI) rejection performance in all tested conditions than NF-P, especially under acidic environments (e.g., pH 4 and pH 5). Moreover, there was a fluctuation of the rejection with the increase of Cr(VI) concentration under acidic environments, which was mainly caused by the formation of Cr 2 O 7 2− species. The harmful Cr(VI) was efficiently removed by the NF membrane with enhanced negative charge under acidic environments, which indicated the wider application range of the NF membrane. [ABSTRACT FROM AUTHOR]

Organic solvent nanofiltration (OSN) has been regarded as a promising membrane-based separation technology with great potential in many fields. In this work, based on the strong electrostatic interaction between nanoparticles (NPs) prepared by the quaternized P(VC- r -DMAEMA) (Q-PVD) and hydrolyzed polyacrylonitrile (HPAN) substrate membranes, separation nanochannels were successfully constructed on the surface of membranes by a one-step coating method. The types of the substrates and concentrations of NPs were optimized to obtain the proper performance. The surface morphology, chemical compositions, surface wettability, surface charge, and pore size were characterized. The obtained thin-film nanocomposite (TFN) membranes exhibited excellent stability in various common organic solvents, such as n -heptane, acetonitrile, ethanol, etc. Furthermore, composite membranes showed excellent retention for dyes with specific molecular weights, with a molecular weight cut-off (MWCO) of 825 Da. In particular, the rejection rates of Coomassie brilliant blue (BB) and Bengal rose red (RB) were 96.6% and 97.9%, respectively. Given the above characteristics, the composite membranes are expected to be used in the field of OSN. [Display omitted] • The amphiphilic copolymer nanoparticles were assembled to construct nanochannels. • The one-step coating method simplified the preparation procedure of OSN TFC membranes. • The membrane showed excellent separation capacity for dyes with specific molecular weights. • Further development of this technology is expected for tailor-made OSN membranes. [ABSTRACT FROM AUTHOR]

To prepare thin film composite (TFC) nanofiltration (NF) membranes with improved flux and rejection performance at low pressure, hyperbranched polyester (HPE) was selected as the nano-sized macromonomer and successfully incorporated into the skin layers on PVC hollow fiber substrates via interfacial polymerization between trimesoyl chloride and the mixtures of hydroxyl-terminated HPE/piperazine (PIP). The resultant NF membranes were characterized using ATR-FTIR, FESEM, AFM and surface zeta potential, while their performance was evaluated in terms of permeate flux and rejection rates of different inorganic salts and neutral solutes. When the HPE content was lower than 60 wt% in HPE/PIP mixtures, the increased membrane surface roughness and the HPE embedded in skin layer effectively enhanced the permeate flux without sacrificing salt rejection for the prepared TFC NF membranes. Further increasing HPE content in HPE/PIP mixtures yielded looser polyamide skin layer, which led to the decline of solute rejection. Due to the larger size and good interfacial compatibility with cross-linked polyamide matrix, the incorporated HPE could exist stably in the skin layer. And thus, the prepared TFC NF membranes showed good flux and rejection stability in a long-term filtration process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Permeation channel was constructed via amphiphilic copolymer nanoparticles packing. • The copolymer nanoparticles were prepared by soap-free emulsion polymerization. • The membrane showed the high selectivity towards amino acids and biopeptides. • This method simplified preparation of NF membrane via nanoparticles packing route. Nanofiltration (NF) as a promising candidate is widely used in charge-based separation of ampholytic biomolecules. Construction of strongly charged permeation channel of NF membrane is one of the key factors for this process. In this work, random amphiphilic copolymer (RACP) nanoparticles were first packed to prepare nanoscale permeation channel. The RACP emulsion was firstly prepared by soap-free emulsion polymerization between [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride (DMC) and methyl methacrylate (MMA), and then directly depositing onto porous substrate to form nanochannel selective layer of NF membrane. The optimal NF membrane shows a relatively large pore structure (i.e., cut-off pore size is 1.43 nm) and high pure water permeance (PWP) of 13.3 L·m−2·h−1·bar−1. Moreover, it shows a desirable rejection of basic amino acids and biopeptides (i.e., ∼95%) and allows neutral or acidic ones with similar molecule weight to permeate through. This work provides an innovative and facile method directly from RACP emulsion to construct NF membrane via nanoparticle packing, which greatly simplifies the preparation procedure for NF membrane. In addition, this novel NF membrane also demonstrates great potential in charge-based separation of biomolecules. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membrane has an extensive application in the field of water treatment, but weakly negative surface-charge and even charge inversion in acidic environment restrict wide applications of traditional aromatic polyamide (PA) thin film composite (TFC) NF membrane in a broad pH range. In this work, 4, 4′-diaminostilbene-2, 2′-disulfonic acid (DSDA), a novel acidic aqueous monomer, was introduced into interfacial polymerization to fabricate a TFC NF membrane with enhanced negative charge and pH stability. The effects of interfacial polymerization parameters were investigated to improve membrane performance. The optimal membrane exhibits a pure water permeance (PWP) of 10.0 ± 0.5 L m−2 h−1·bar−1 and a high Na 2 SO 4 rejection (i.e., ~97.0%). The resultant membrane remains a strongly negative charge when the pH value is changed from 2 to 12. Due to enhanced negative charge, Donnan exclusion plays a significant role in membrane separation process, which results in a huge superiority in removal of Na 2 SO 4 , Na 3 PO 4 and K 2 Cr 2 O 7 in a broad pH range especially in acidic environment. Hence, it is demonstrated that the negative-charged NF membrane prepared in this work has improved and stable separation performance under a broad pH range, which expands application scopes of NF membrane, especially in removing Cr (VI) and phosphate in acidic environments. Besides, this study also provides a feasible route for preparation of suitable TFC NF membrane for working in acidic environment via introducing strongly acidic groups in selective layer. [Display omitted] • The thin film composite nanofiltration membrane with enhanced negative charge was fabricated. • A novel monomer-4, 4′-diaminostilbene-2, 2′-disulfonic acid was used for interfacial polymerization. • The membrane had great superiority in removal of Cr (VI) and phosphate in acidic environment. • This novel membrane expands the application range of nanofiltration in wastewater treatment. [ABSTRACT FROM AUTHOR]

High-efficient separation of molecules is of great significance in food, biotechnology, pharmaceutical and dairy industries. To this end, cationic hyperbranched poly (amido-amine)s (HBPs) with different numbers of quaternary ammonium groups were employed as a new kind of 3D spherical macromonomers to fabricate nanofiltration (NF) membranes, through interfacial polymerization (IP) between cationic HBPs and trimesoyl chloride (TMC) on a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane surface. Apart from the inner voids inside cationic HBP molecules for fast transport of water molecules, sizes and charge properties of the outer voids between cationic HBP molecules can be modulated by changing the numbers of quaternary ammonium groups on cationic HBP molecule surfaces for enhancing both high permeability and selectivity (water permeance and MgCl 2 rejection rate of the resultant NF membrane are up to 310.5 L m−2 h−1 MPa−1 and 92.0% respectively). Based on the separation mechanism of combined steric and Donnan effects, the resultant NF membrane exhibits ultrahigh retentions to molecules with high molecular weights (MWs) or positive charges, thus molecular-level selectivity to VB12/VB2 (neutral molecules with distinct MWs) or VB1/VB2 (cationic/neutral molecules with similar MWs) can be achieved. [Display omitted] • Cationic HBPs were synthesized as a novel kind of macromonomers for IP. • Nanochannel in NF membrane selective layers were engineered by cationic HBPs. • HBP-TAC2/TMC membrane exhibits higher water permeability and MgCl 2 rejection. • Separation of molecule mixtures can be achieved based on steric and Donnan effects. [ABSTRACT FROM AUTHOR]

Nanofiltration membranes (NFMs) with negatively-charged nanochannels (NCNs) are of critical significance for enhancing the rejection of divalent anions. Herein, NFMs with NCNs are fabricated through a facile coating-heating route. Sulfonated polysulfone (SPSF) nanoparticles (13–40 nm) dispersed in aqueous phase are used to generate a dense layer on PES ultrafiltration (UF) membranes with different molecular weight cut-off (MWCO). It is found that the differences in the roughness of the substrates have significant contributions to the packing process of the SPSF nanoparticles, which indicate the smooth surface can be the better one. Scanning electron microscopy (SEM) images suggest the successful fabrication of the dense layer about 200 nm on different substrates. The resultant membranes feature selective layers with the nanochannels from 0.7 to 1.2 nm in average and zeta potential measurements indicate the nanochannel layers are negatively charged, causing the salts rejection in the following sequence: Na 2 SO 4 > NaCl > MgSO 4 > MgCl 2. Furthermore, the constructed membranes exhibit an excellent separation performance with the water flux of 7.2 L m−2 h−1 bar−1 and the rejection rate for Na 2 SO 4 of 94%, which demonstrates a novel economic and effective approach towards fabrication of nanofiltration membranes. Image 1 • Negatively-charged nanochannels were successfully fabricated from aqueous sulfonated polysulfone nanoparticles. • A smoother substrate is benefit to the coating of the SPSF nanoparticles for a better performance. • The prepared nanofiltration membranes exhibited enhanced rejection of divalent anions. [ABSTRACT FROM AUTHOR]