Ultrathin Membrane Sifts Oil From Water

Researchers in Japan have coated a polymer with silica to devise a membrane that effectively separates oil from water.

AsianScientist (Jan. 17, 2020) – Oil and water don’t mix, but when an oil spill occurs, separating the two liquids can be extremely difficult. Scientists in Japan have developed an ultrathin membrane that could be used in the clearing up of oil pollution in various contexts. Their findings are published in the Journal of Materials Chemistry A.

Compared with traditional purification methods including centrifugation and chemical coagulation, membrane separation has been proposed as a low cost, energy efficient method to remove oil from water. However, most existing membranes suffer from fouling issues, whereby droplets of oil get irreversibly absorbed onto the surface. This leads to membrane pore blocking, subsequently reducing the membrane’s lifespan and efficiency.

To recover membrane function, surface treatments with strong acid, alkaline and salt solutions may be used. Unfortunately, these treatments also alter the original surface structure of the membrane surface, leading to deterioration of the membrane material.

In this study, researchers led by Professor Matsuyama Hideto and Professor Yoshioka Tomohisa at Kobe University’s Research Center for Membrane and Film Technology, Japan, have succeeded in developing an ultrathin membrane with a fouling-resistant surface for high performance separation of oil from water.

The team used a porous polyketone (PK) support with a ten-nanometer thick silica layer applied on the top surface. This silica layer was formed onto the PK fibrils using electrostatic attraction—the negatively charged silica was attracted to the positively charged PK.

The PK membrane exhibited a high water permeance due to its large pores and high porosity. Meanwhile, the addition of silica to the PK fibrils provided a strong oil-repellant coating to protect the membrane.

The researchers noted that another advantage of their membrane is that it requires no large pressure application to achieve high water penetration. The membrane exhibited water permeation by gravity, even when the water level was as low as 10 cm.

In addition, their membrane was able to reject 99.9 percent of oil droplets, including those as small as 10 nanometers in size. Oil did not become adsorbed onto the surface of the membrane, so oil droplets could be easily cleaned off.

The researchers estimate that 6,000 liters of wastewater can be treated in one hour under an applied pressure of 1 atmosphere using a 1 m2 membrane. They also demonstrated that their membrane could tolerate a variety of acidic, alkaline, solvent and salt solutions. In the future, the membrane could be used in the treatment of industry waste water, the researchers said.

The article can be found at: Zhang et al. (2019) An Ultrathin in situ Silicification Layer Developed by an Electrostatic Attraction Force Strategy for Ultrahigh-performance Oil–water Emulsion Separation.


Source: Kobe University; Photo: Unsplash.
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