Preparation and separation properties of polyamide nanofiltration membrane

A nanofiltration membrane prepared by PDA-C3N4 for removal of divalent ions

In this study, a positively charged nanofiltration (NF) membrane was prepared by interfacial polymerization for separation of divalent cations, whereby a nanomaterial (modified graphitic carbon nitride (g-C₃N₄) with poly(dopamine), PDA-C₃N₄) was incorporated into the active layer of the NF membrane. PDA-C₃N₄ sheets were synthesized from g-C₃N₄ sheets prepared by thermal oxidation of melamine, and the preparation conditions of NF membrane were also optimized. The results show that the roughness of PDA-C₃N₄ embedded NF membrane decreases, and the hydrophilicity and the permeation increase. The membrane also shows high rejection for divalent cations (Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺ and Zn²⁺) but low rejection (36.8%) for monovalent cation (Li⁺), as well as good fouling resistance performance. The fabricated membrane has the potential for treatment of industrial wastewater.

Degradation of Polyamide Membranes Exposed to Chlorine: An Impedance Spectroscopy Study

Polyamide is the key material in modern membrane desalination; however, its well-known and incompletely understood drawback is its low tolerance to chlorine, the most efficient in-line disinfectant. Here we report a first investigation of the mechanism and kinetics of chlorine attack using electrochemical impedance spectroscopy (EIS) that directly probes changes in ion permeation upon chlorination at different pH values, focusing on its early stages and low chlorine concentrations (15-197 ppm). EIS results partly conform to an established two-stage mechanism that proceeds as N-chlorination followed by either C-chlorination in acidic conditions or amide bond scission in alkaline conditions. However, early time kinetics in acidic conditions shows inconsistencies with this model, explained by possible effects of direct ring chlorination and finite polymer relaxation rates. The findings indicate that (a) N-chlorination reduces membrane polarity and ion permeability, while C-chlorination has an opposite effect; (b) chlorination in acidic conditions must involve other reactions, such as direct ring chlorination, in addition to N-chlorination and Orton rearrangement; and (c) the ultimate chemical transformations (C-chlorination or amide bond scission) result in an irreversible increase in membrane polarity and loss of ion rejection. The results highlight the potential of EIS as a powerful and sensitive tool for studying chemical degradation of ion-selective materials that may assist in developing new chlorine-resistant membranes.

Tailoring polyamide thin film composite nanofiltration membranes by polyethyleneimine and its conjugates for the enhancement of selectivity and antifouling property

Post modification of poly(piperazineamide) membrane with polyethyleneimine conjugates provides membranes with novel properties such as high monovalent to divalent ion selectivity and improved antifouling properties, suitable for water purification.

Preparation and performance of silver nanoparticle incorporated polyetherethersulfone nanofiltration membranes

Studies on the preparation of nanofiltration (NF) membranes with silver nanoparticle (Ag-Np) were conducted. The membranes were synthesized with different concentrations of Ag-Np by the phase inversion method, using 1-methyl-2-pyrrolidone (NMP) as the solvent and deionized water as the coagulant. Ag-Np was prepared by the simple chemical reduction method. The formation, structure, morphology and size of Ag-Np were characterized by ultraviolet–visible spectroscopy, x-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polyetherethersulfone/Ag-Np flat-sheet membranes were prepared by the phase inversion method and investigated in terms of compaction, pure water flux, water content, hydraulic resistance, molecular weight cut-off (MWCO), porosity, hydrophilicity and mechanical properties. The morphology of the membranes was studied by SEM. The elemental composition of the membranes was evaluated by energy dispersive x-ray (EDX). Performance of the membranes was evaluated by mono and divalent metal ion rejection studies. Antibacterial activity studies of the membranes were evaluated by the Muller-Hinton disk diffusion method, against the gram negative (bacterium) of Escherichia coli ( E.coli) and the gram positive bacterium of Staphylococcus aureus (S. aureus). The results revealed that the incorporation of Ag-Np increases the performance of the membranes.

Solvent resistant nanofiltration: separating on a molecular level

Over the past decade, solvent resistant nanofiltration (SRNF) has gained a lot of attention, as it is a promising energy- and waste-efficient unit process to separate mixtures down to a molecular level. This critical review focuses on all aspects related to this new burgeoning technology, occasionally also including literature obtained on aqueous applications or related membrane processes, if of relevance to understand SRNF better. An overview of the different membrane materials and the methods to turn them into suitable SRNF-membranes will be given first. The membrane transport mechanism and its modelling will receive attention in order to understand the process and the reported membrane performances better. Finally, all SRNF-applications reported so far - in food chemistry, petrochemistry, catalysis, pharmaceutical manufacturing - will be reviewed exhaustively (324 references).