A team of researchers at the University of Manchester has developed a new technology that will address one of the biggest issues in membrane technology. Published in the journal Nature Communications, the team describes how they can overcome the problem of membrane fouling by using the exfoliated two-dimensional form of vermiculite as a fouling resistant coating for oil-water separation.
2D Materials Show Promise in Solving Fouling Problem
Various processes rely on membrane-based separations like water filtration as well as oil and gas separation. Fouling is a major problem in this process. It describes the common occurrence where pores in the membrane become blocked, having the effect of preventing the flow of substances through the membrane. Oil separation technology is particularly vulnerable to fouling because of the ease at which oil droplets attach themselves to the membrane’s surface.
Currently, graphene and other 2D materials are being used to address this problem as they have been shown to filter the impurities in ways previously thought impossible. The team at Manchester set out to improve on this and aimed to create a new method using a 2D material to facilitate the separation of oil to overcome the problem of fouling.
Decreasing Oil Adhesion
A known solution to reducing membrane fouling caused by oil deposition is to increase the wettability of water and to decrease the adhesiveness of oil. Previously, scientists have focussed on developing methods to enhance water wettability, whereas techniques focussing on decreasing the adhesiveness of oil have been neglected. While attempts to increase water wettability have been successful, a long-term solution to fouling has yet to be achieved.
The Manchester-based team aimed to resolve this. Their research led to the discovery that it is possible to tune the wetting properties of vermiculite membranes from super-hydrophilic to hydrophobic by facilitating an exchange of cations from the surface to the layers of vermiculite.
In addition, the researchers also showed that this property could be exploited by commercial microfiltration membranes in a coating of superhydrophilic lithium exchanged vermiculite (lithium vermiculite).
This lithium coating provides superhydrophilicity as well as superoleophobicity which repels oil droplets. Tests demonstrated that the vermiculite coated microfiltration membranes showed a 40 lower under-water oil adhesion than the noncoated membrane.
The team believes that their innovation will not only solve the problem of membrane fouling, but it will also be adaptable to applications such as antifouling filters for biofiltration and self-cleaning surfaces.
A successful long-term approach to resolving membrane fouling has long eluded researchers, leading to problems facing technologies involved in water filtration as well as oil and gas separation. The Manchester-based team of scientists has significantly advanced the understanding of wetting properties of solids at the level of the molecule. Their innovation will enable the development of more effective fouling resistant membrane technologies in the future.
The findings of the study elucidate details regarding how water molecules interact with surfaces and ions at the atomic-scale. The scientists explain how water molecules arrange themselves in a unique format on the surface of lithium vermiculite, which allows it to have a high affinity for water, and therefore, a reduced oil droplet interaction.
In addition, ions present on the surface of the vermiculite membrane facilitated the adhesion of water molecules onto the vermiculite membrane, a property that was apparent even when the vermiculite had been exposed to oil over a long time period. This unique characteristic of the vermiculite coated membrane will likely see it being adopted in the development of other similar technologies and is expected to be successful as a long-term antifouling coating, improving the functioning of water filtration and oil and gas separation.