Electrospraying a better desalinization membrane

August 16, 2018

Following 30 years during which the membrane hasn't changed much, researchers have introduced a new method for making the membranes used to turn saltwater fresh. Commercial water desalination makes use of thin composite membranes that feature an ultrathin layer of a polyamide film full of pores. The pores are large enough to allow water to flow through, but too small for salt ions in saltwater to slip by. These films are grown on the surface of the composite membranes through a chemical reaction between an amine in a water phase and an acid chloride in an oil phase. However, this method results in a relatively thick and rough polyamide film (between 100 and 200 nanometers in thickness), which impact the desalinization efficiency of the membrane. Despite the processes' limitations, it's remained the industry standard for decades. Here, Maqsud Chowdhury et al. advance an additive method of polyamide formation, which allows for greater control over both the thickness and texture of the ultrathin films, by building them layer by molecular layer. According to the authors, while others have advanced similar approaches, the complex methods involved in their approaches are difficult to scale for commercial production. Chowdhury et al., by contrast, used an electrospray technique. In this method, high-voltage, nanoscale droplets of monomers are finely dusted onto a substrate where they combine to form the polyamide film. The electrospray technique was able to produce films as thin as four nanometers and with greatly improved surface roughness . Furthermore, the results suggest better desalinization performance than currently available reverse osmosis membranes.
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American Association for the Advancement of Science

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