Indian Institute of Technology Guwahati Researchers have developed two distinct and special membranes that can separate oil and water, even under harsh conditions. The membranes that are super-water repellent in air, and super oil-repellent in water, can separate complex mixtures of oil and water at practically relevant settings. Oil-water separation is all the more important considering its environmental applications like oil spill management.
The research led by Dr. Uttam Manna, Assistant Professor, Department of Chemistry, IIT Guwahati along with his research team Mr. Avijit Das, Ms. Dibyangana Parbat and Ms. Arpita Shome was published in ACS Sustainable Chemistry & Engineering.
The team then developed a prototype of oil-water separation device using these membranes such that the separated oil and water were simultaneously collected in different containers.
Speaking on the need to develop materials that can separate oil and water, Dr. Uttam Manna said, "Oil-water separation is of current relevance because many industries, such as mining, textiles, food and petrochemicals, produce massive volumes of oily wastewater, which must be treated before discharge."
There have been many studies on materials and techniques that can separate oil and water. In recent times, materials scientists have taken cues from nature, for this purpose. The lotus leaf for example, is water repellent so that it does not get soggy in its living space. Fish, on the other hand, has a body surface that repels oil in order to survive in polluted waters.
Scientists have studied the surface structures of lotus leaves and fish scales to understand what gives them their superhydrophobicity (super-water repellence) and superoleophobicity (super-oil repellence), respectively, so that these structures can be replicated artificially for oil-water separation applications. Thus, lotus leaf-inspired superhydrophobic materials and fish scale-inspired superoleophobic materials have been developed--following a single and unique deposition process and tested for gravity-driven removal of oil from water.
While these bio-inspired membranes are individually used to separate oil and water in the recent past, there is accumulation of water or oil on the membrane over time, which blocks further separation.
"There is yet another problem with conventional demonstration, where the superhydrophobic and superoleophobic materials are mostly used for two phase oil/water mixtures. However, those approaches are inappropriate for separation of three-phase mixtures of heavy oil, light oil and water," added Dr. Manna.
In addition, these materials are required to operate under harsh conditions; these materials are subjected to severe stretching and bending during operation, which make them physically unstable.
In order to overcome the above problems, Dr. Manna and his team developed a system of 'super liquid repellent' materials, by combining the lotus leaf superhydrophobicity and fish scale superoleophobicity. Layer-by-layer deposition technique was used to obtain alternating layers of 'chemically reactive polymeric nano-complex' and 'amino graphene oxide nanosheets' on a stretchable and fibrous substrate.
The durable and stretchable membranes that the team developed were super-water-repellent in air and super-oil-repellent in water.
"These separation systems allow continuous, parallel and selective separation of various oil/water mixtures, irrespective of surface tension, density, and viscosity of the oil phase and chemical complexity in the water phase", Dr. Manna said while explaining the design of the device.
Not stopping with preliminary testing of these membranes, the research team expanded testing to study the performance of the membranes from three phase oil/water mixtures under severe conditions such as extremes of pH, artificial seawater, river water, etc. They found that the separation performance was excellent even after exposure to extreme conditions.
Some important and relevant applications for such special surfaces are anti-biofouling coatings, oil-water separation for both industrial purposes and for treating oil spills and other such environmental catastrophes, etc.
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