A multidisciplinary initiative involving several research institutes based in the United Kingdom have discovered a new means of separating oil and water that uses the exfoliated two-dimensional (2D) form of a natural clay material known as vermiculite as a fouling resistant coating.
The research team includes members of three research institutes located in the University of Manchester (Manchester, United Kingdom): the Department of Chemical Engineering & Analytical Science, the Henry Royce Institute, and the National Graphene Institute. Researchers from these three Manchester institutes collaborated with researchers from University College London (UCL) (London, United Kingdom) in the study that was published in Nature Communications.
According to a university press release, the research team has made significant progress in overcoming membrane fouling, one of the biggest obstacles in membrane technology. During membrane separation, fouling will inevitably occur as a result of blockages in membrane pores. These blockages prevent the normal operations of a membrane by stopping the flow of water and causing oil droplets to stick onto its surface.
However, Manchester researchers have learned that vermiculite membranes have wetting properties that can be tuned from hydrophobic, meaning that it repels water, to hydrophilic, meaning that it can be wetted by water. There is broad consensus in the scientific community that membranes with increased wettability and decreased oil adhesion can reduce fouling—however, attempts to develop such hydrophilic materials as antifouling coatings were not successful over the long term.
By contrast, the technique pioneered by the Manchester researchers involves stacking multiple layers of 2D vermiculite sheets that are made super-hydrophilic by exchanging the cations present on the surface and between the layers of vermiculite. “Developing antifouling membranes for oil-water separation is a long-sought objective for scientists and technologists, which is evident from the rapid growth in the number of publications in this area,” says Rahul Raveendran Nair, a professor of materials physics at the University of Manchester.
In addition, the research team used superhydrophilic lithium-exchanged vermiculite (lithium vermiculite) as a coating layer for commercial microfiltration membranes, which will reduce membrane fouling during oil-water filtration.
“Lithium vermiculite membranes not only provide superhydrophilicity but also repel oil droplets during filtration due to their underwater superoleophobic property,” says Kun Huang, a PhD student at the University of Manchester and the lead author of the paper in Nature Communications. “The under-water oil adhesion on vermiculite coated microfiltration membranes was more than 40 times lower than the noncoated membrane.”
Membrane-based separations have a number of useful applications in such processes as water filtration and oil and gas separation. The use of 2D materials in membrane technology has attracted researchers who see potential in the tunability of these materials. The superhydrophilic antifouling membranes developed by the Manchester team could be expanded to other areas such as developing self-cleaning surfaces and antifouling filters for biofiltration, the researchers claim. “We believe our work provides a major advance in the fundamental understanding of wetting properties of solids down to the molecular level and is a notable milestone in the development of robust fouling resistant membrane technologies,” says Nair.
Source: University of Manchester, www.manchester.ac.uk.