Soaking up oil spills with nanowires

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Source: European Commission, Environment DG

Oil spills and other industrial chemical leaks can cause havoc in ecosystems, killing marine and aquatic wildlife and polluting drinking water supplies. New research has developed a way of cleaning up spills using a super-absorbent material, which selectively draws up oil and other organic pollutants, leaving clean water behind. Current methods for cleaning up oil spills have limitations. Many currently available clean-up chemical spills simply disperse the spilled chemical. Although less concentrated, the chemicals remain in the water. In the case of oil spills, detergents are usually added to the water to disperse the oil. These detergents may cause further damage to delicate ecosystems such as coral reefs. A new super-absorbent material may overcome these problems by removing the spilled oil or chemicals from the polluted water, rather than simply dispersing them.

The new material is in the form of a large mat that looks and feels similar to paper. It is made from a mesh of manganese oxide nanowires, which are a few nanometres (one billionth of a metre) and just a few atoms thick. At the nanoscale, materials can be made that have properties that are completely different than materials made from the same compounds but on a larger, bulkier scale. In the case of the manganese oxide sheet, the huge number of pores the material contains and its vast surface area (44m2 per gram) make it highly absorbent. The research showed that this new material could absorb up to 20 times its own weight in oil and industrial organic solvents.

To adapt the super-absorbent material into an environmental clean-up tool for use in polluted water, the researchers developed a method of coating it with a water repelling layer of silicone. The coated material selectively absorbs oil, leaving clean water behind. The water repellant layer can be removed afterwards by heating the sheet. This allows the oil to be removed from the material. The manganese oxide sheet can be used many times. After each use, the nanowires can be reassembled to form a new mat and recoated with silicone. Oil and chemicals recovered using the sheet can also be used.

The researchers tested the ability of the sheet to absorb a number of organic pollutants - including gasoline and motor oil - and found that the material was able to absorb these liquids from water within a fraction of a second. Given the global scale of severe water pollution, and the increasingly important issue of water security, there is a growing interest in developing materials such as this one. The methods used to design this mat could be used to design similar, recyclable absorbent materials that can be used as water purification instruments. Such an approach would offer wider benefits to the environment.

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