IIT Guwahati uses superhydrophobic cotton to remove oil – spill

IIT Guwahati uses superhydrophobic cotton to remove oil – spill

Context

A team of Researchers at the Indian Institute of Technology (IIT) Guwahati has removing up to 95% of oil-spill of different densities, light and heavy oils, repetitively at least 100 times using super hydrophobic (extremely water repelling) medical cotton.

What was the experiment?

• The researchers turned the medical cotton, which is extremely water absorbing, into a super hydrophobic (water contact angle of 157 degrees) material and used it for absorbing oil both in air and under water.
• The efficacy of absorption is very high, above 2,000 weight percentage for both heavy and light oils.
• One gram of the super hydrophobic cotton absorbs 20 grams of either heavy or light oils. The results were published in the Journal of Materials Chemistry A.
• The absorbed oil can be recovered through physical compression. The super hydrophobicity remained intact even when the cotton was manually compressed up to 1,000 times and subjected to other physical manipulations.

Other characteristics of the experiment

• It has the ability to absorb oil from three complex phases — light oil that floats in the air–water interface, sediment oil that settles at the bottom as it is heavy, and from water-in-oil emulsion.
• The super hydrophobic property remains intact even when exposed to UV light for ten days, the material was able to absorb oil from river and sea water, and extremely acidic (pH 1) and alkaline (pH 12) water.

Treating emulsions

• The cotton is inherently incompetent of removing oil from oil-in-water emulsion.
• In the case of oil-in-water emulsion there is very little of oil present and as there is more water present, the super hydrophobic material does not come in contact with oil and thus it is unable to remove oil efficiently from oil-in-water emulsion.

Filtering oil

• Selective filtration of oil under water against gravity in the case of heavy oil that has settled at the bottom was achieved.
• To conduct the experiment, the researchers plugged one end of a tube with the super hydrophobic cotton and dips the tube so it comes in contact with the oil.
• Once in contact with the sediment oil, the cotton absorbs the oil and due to hydraulic pressure, the oil gets removed from the cotton and accumulates inside the tube.
• In the case of gravity-driven filtration, heavy oil mixed with water is poured into a funnel, the tip of which is closed with the super hydrophobic cotton. The heavy oil settles to the bottom and comes in contact with the cotton which filters it leaving the water in the funnel.
• This method can be used in industry to remove the oil component from water before letting out the waste water.

Cotton processing

• The hydroxyl group seen in cotton is first modified with branched poly (ethylenimine (BPEI) to make it functionalized with amine group.
• A nanocomplex is prepared separately by mixing BPEI with dipentaerythritol pentaacrylate (5Acl) and added to the functionalised cotton.
• The nanocomplex provides essential topography and makes the cotton chemically reactive, thus making it possible to further optimize the appropriate chemistry of the material.
• The nanocomplex reacts with amine-based small molecules of choice to make the cotton hydrophobic to varying degrees.
• The hydrophobicity from hydrophilic can be tuned to super hydrophobic using different amine-containing small molecules
• It is a green synthesis without the use of any catalyst or hazardous material. The process of making super hydrophobic cotton is a simple three-step process and scalable.

What is Super hydrophobic coating?

• A superhydrophobic coating is a nanoscopic surface layer that repels water. Droplets hitting this kind of coating can fully rebound in the shape of column or pancake.
• In industry, super-hydrophobic coatings are used in ultra-dry surface applications. The coating causes an almost imperceptibly thin layer of air to form on top of a surface.
• Super-hydrophobic coatings are also found in nature; they appear on plant leaves, such as the Lotus leaf, and some insect wings.
• The coating can be sprayed onto objects to make them waterproof. The spray is anti-corrosive and anti-icing; has cleaning capabilities; and can be used to protect circuits and grids.

Use of super hydrophobic coating

• Due to the extreme repellence and in some cases bacterial resistance of hydrophobic coatings, there is much enthusiasm for their wide potential uses with surgical tools, medical equipment, textiles, and all sorts of surfaces and substrates.
• However, the current state of the art for this technology is hindered in terms of the weak durability of the coating making it unsuitable for most applications.
• Newer engineered surface textures on stainless steel are extremely durable and permanently hydrophobic.
• Optically these surfaces appear as a uniform matte surface but microscopically they consist of rounded depressions one to two microns deep over 25% to 50% of the surface. These surfaces are produced for buildings which will never need cleaning.