Ultrasonic irradiation can break down ionic liquids into more environmentally benign compounds, say scientists.

Ionic liquids are widely regarded as a greener alternative to many commonly used solvents. But, concerns about their toxicity have raised questions about their use in large scale industrial applications, especially those that involve the creation of large amounts of waste.

High frequency sound waves break ionic liquids into non-toxic components. Image: Chemical Science

A team of researchers at the South China University of Technology, Guangzhou, and the University of Reading, UK, used ultrasound irradiation - very high frequency sound waves - on solutions of hydrogen peroxide, acetic acid and dialkylimidazolium based ionic liquids. The dialkylimidazolium groups broke down to non-toxic biurea and acetoxyacetic acid.

'We have studied many degradation processes,' said team member Xuehui Li, who is currently based in Reading, 'and so far, this is the most efficient. However, we think that this can be improved by using a catalyst, and we are now investigating possible catalysts that may enhance the degradation process.'

Chris Hardacre at Queen's University Belfast, UK, who studies the use of ionic liquids in chemical processing, said, 'Li's study represents an important contribution on the treatment of wastewater containing ionic liquids. More research is needed in this area and the process reported will stimulate this vital area of research.'

Ultrasonic chemical oxidative degradations of 1,3-dialkylimidazolium ionic liquids and their mechanistic elucidations
Xuehui Li, Jinggan Zhao, Qianhe Li, Lefu Wang and Shik Chi Tsang, Dalton Trans., 2007
DOI: 10.1039/b618384k