Search

[Display omitted] • Cationic poly(amido-amine)s (PAMAMs) were synthesized for a novel PA nanofilm. • Cationic PAMAM incorporated polyamide (PA) nanofilm is Janus charged. • Selectivity of the Janus charged PA nanofilm to mono-/divalent ions is up to 65. • The Janus charged PA nanofilm shows enhanced hard water softening performance. Nanofiltration (NF) membranes with ultra-high separation selectivity to both mono-/divalent anions and cations are desirable for treatment of practical water with complex composition of ions. In this work, a facile and universal method for fabricating polyamide (PA) NF membranes with both ultra-high separation selectivity to mono-/divalent anions and cations was developed. Cationic poly(amido-amine) (PAMAM) dendrimers with different numbers of terminal quaternary ammonium groups were synthesized and incorporated into the polyamide (PA) matrix by interfacial polymerization (IP) to modulate both charge properties and network structures of the PA nanofilms. Contributed by the heterogenous distribution of PAMAM G5-TAC2, a Janus charged PA nanofilm was successfully fabricated. The negatively charged top surface of the PA nanofilm leads to a high electrostatic repulsion to divalent anions while its positively charged back surface exerts a high electrostatic repulsion to divalent cations. Moreover, the network structures of the PA nanofilms are precisely modulated to accelerate the transport of water molecules (103.5 L m−2h−1 MPa−1). Based on the synergistic effect of steric and Donnan effects, the transports of both divalent anions and cations through the G5-TAC2/PIP membrane are hindered, while the transports of monovalent ions are free, so that both ultra-high separation selectivity to mono-/divalent anions and cations (both above 65) can be achieved. Compared to PIP only membrane, G5-TAC2/PIP membrane exhibits high-efficiency in mixed ion separation process. [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 (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]

Nanoscale permeation channels are a key factor for molecules or/and ions separation in membrane field. In this work, molecular deposition strategy is designed to construct high-performance nanochannel separation layer for selective separation of small molecules. Herein, octaammonium polyhedral oligomeric silsesquioxane (8NH 3 Cl-POSS) and tannic acid (TA), two kinds of multifunctional molecules with a size of about 1 nm, were used to prepare robust and perm-selective composite membrane through covalently-bonded layer-by-layer (LbL) self-assembly method. The optimized TA-POSS composite membrane exhibited a narrowed pore size distribution from 0.3 to 1.6 nm with a high water permeance of 21 L m−2 h−1 bar−1. The membrane showed desirable rejection of antibiotics (>90%) and enabled to separate them from NaCl solution. In addition, TA-POSS composite membrane showed outstanding stability due to the high degree of crosslinking between TA and 8NH 3 Cl-POSS and their rigid structures. This work gives a novel and green strategy to construct nanochannel composite membranes, which can efficiently separate molecules and salt. Image 1 • TA-POSS membrane was prepared by covalently-bonded LbL self-assembly method. • The membrane showed a permeance of 21 LMH/Bar with MWCO of 440 Da. • The membrane enabled to efficiently separate the antibiotics and NaCl solution. • The membrane showed good stability performance due to the cross-linked structure. [ABSTRACT FROM AUTHOR]