Preparation and characterization of a composite nanofiltration membrane interfacially polymerized fromcis,cis-1,3,5-triaminocyclohexane and trimesoyl chloride

Preparation of Layer-by-Layer Nanofiltration Membranes by Dynamic Deposition and Crosslinking

In recent decades, the advancements in layer-by-layer (LBL) assembly technology have provoked increasing interest in the preparation of multilayer polyelectrolyte membranes with excellent performance. In the current study, a novel nanofiltration (NF) membrane was prepared by pressure-driven layer-by-layer (LBL) assembly of polyethylenimine (PEI) and polyacrylicacid (PAA) on a porous substrate with chemical crosslinking. The effect of deposition pressure on separation performance of the prepared membranes was studied. The surface morphology, hydrophilicity and the charge property of the dynamically-deposited membranes were compared with those prepared by static adsorption. The characterization results showed that dynamic deposition process resulted in a smoother membrane surface with improved hydrophilicity. The mechanism of water-path formation was proposed to interpret the effect of pressure on the membrane performance. Glutaraldehyde (GA) was used as a crosslinker to reduce the number of polyelectrolyte bilayers for obtaining good separation performance. The rejections of different inorganic salts of the dynamically-deposited NF membrane were also investigated.

Tannic Acid/Fe3+ Nanoscaffold for Interfacial Polymerization: Toward Enhanced Nanofiltration Performance

Conventional thin-film composite (TFC) membranes suffer from the trade-off relationship between permeability and selectivity, known as the "upper bound". In this work, we report a high performance thin-film composite membrane prepared on a tannic acid (TA)-Fe nanoscaffold (TFC_n) to overcome such upper bound. Specifically, a TA-Fe nanoscaffold was first coated onto a polysulfone substrate, followed by performing an interfacial polymerization reaction between trimesoyl chloride (TMC) and piperazine (PIP). The TA-Fe nanoscaffold enhanced the uptake of amine monomers and provided a platform for their controlled release. The smaller surface pore size of the TA-Fe coated substrate further eliminated the intrusion of polyamide into the substrate pores. The resulting membrane TFC_n showed a water permeability of 19.6 ± 0.5 L m^2- h^-1 bar^-1, which was an order of magnitude higher than that of control TFC membrane (2.2 ± 0.3 L m^-2 h^-1 bar^-1). The formation of a more order polyamide rejection layer also significantly enhanced salt rejection (e.g., NaCl, MgCl₂, Na₂SO₄, and MgSO₄) and divalent to monovalent ion selectivity (e.g., NaCl/MgSO₄). Compared to conventional TFC nanofiltration membranes, the novel TFC_n membrane successfully overcame the longstanding permeability and selectivity trade-off. The current work paves a new avenue for fabricating high performance TFC membranes.