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[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]

[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]

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]

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]

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]

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]