Abstract
A practical method is reported to enhance water permeability of thin film composite (TFC) polyamide (PA) membranes by decreasing the thickness of the selective PA layer. The composite membranes were prepared by interfacial polymerization (IP) reaction between meta-phenylene diamine (MPD)-aqueous and trimesoyl chloride (TMC)-organic solvents at the surface of polyethersulfone (PES) microporous support. Several PA TFC membranes were prepared at different temperatures of the organic solution ranging from −20 °C to 50 °C. The physico-chemical and morphological properties of the synthesized membranes were carefully characterized using serval analytical techniques. The results confirmed that the TFC membranes, synthesized at sub-zero temperatures of organic solution, had thinner and smoother PA layer with a greater degree of cross-linking and wettability compared to the PA films prepared at 50 °C. We demonstrated that reducing the temperature of organic solution effectively decreased the thickness of the PA active layer and thus enhanced water permeation through the membranes. The most water permeable membrane was prepared at −20 °C and exhibited nine times higher water flux compared to the membrane synthesized at room temperature. The method proposed in this report can be effectively applied for energy- and cost-efficient development of high performance nanofiltration and reverse osmosis membranes.
Highlights
Membrane separation technologies, mainly nanofiltration (NF) and reverse osmosis (RO), have secured an important role in available water purification processes as a promising single step technique for removing multiple sized solutes and organic pollutants from contaminated water
Before proceeding to examine the effect of the organic solution temperature on the properties of the PA thin film composite (TFC) membranes, it is necessary to understand the mechanism of the interfacial polymerization (IP) reaction
Any variation in the thermodynamic properties of the organic solution is expected to change the solubility, diffusion and partitioning of the MPD molecules into the reaction zone which changes the rate of the polymerization reaction, the final surface morphology and permselectivity of the TFC membranes
Summary
Mainly nanofiltration (NF) and reverse osmosis (RO), have secured an important role in available water purification processes as a promising single step technique for removing multiple sized solutes and organic pollutants from contaminated water. Recent advances were focused on improving the membrane synthesis protocols[10,11], modifying the surface properties by grafting additional polymer onto the surface[12,13] and on developing nanocomposite membranes by the incorporation of hydrophilic metal oxide nanofillers, nanoporous zeolite particles, carbon nanotubes and graphene oxide nanosheets[14,15,16,17,18,19] Most of these efforts have shown promising results in the lab-scale, they are still faced with the challenges of cost-efficient synthesis process and easy scale-up for high volume industrial practices[20]. The improved performance of the TFC membranes (water flux and salt rejection) was correlated to changes in the chemical and morphological structures of the selective layer which were imparted by the variation of the organic solution temperature
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