New Delhi: Researchers at the Indian Institute of Technology (IIT) Guwahati have developed a device that can continuously separate oil from water by strategic use of fish-scale and lotus-leaf inspired membranes.
The team developed the system of materials by combining the lotus leaf-inspired super-water repellence and fish scale-mimicked underwater super-oil repellence.
The membranes that are super-water repellent in air, and super oil-repellent in water, have been shown to separate complex mixtures of oil and water at practically relevant settings, according to the journal ACS Sustainable Chemistry & Engineering.
Oil-water separation is also important in environmental applications like oil spill management.
The team then developed a prototype of oil-water separation device using these membranes so that the separated oil and water were simultaneously collected in different containers.
“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,” said Uttam Manna, Assistant Professor, Department of Chemistry, IIT Guwahati.
The lotus leaf for example, is water repellent so that it does not get soggy in its living space, researchers said. Fish, on the other hand, has a body surface that repels oil in order to survive in polluted waters, they said.
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), so that these structures can be replicated artificially for oil-water separation applications.
Lotus leaf-inspired superhydrophobic materials and fish scale-inspired superoleophobic materials were 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,” Manna said.
“However, those approaches are inappropriate for separation of three-phase mixtures of heavy oil, light oil and water,” he said.
These materials are required to operate under harsh conditions; they are subjected to severe stretching and bending during operation, which make them physically unstable, researchers said.
In order to overcome the problems, 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,” Manna said.