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The nano way to cleaner water

Published 14 February 2012

Decontaminating polluted waste water costs millions but a new discovery by scientists at the University of Brighton could result in huge savings as well as delivering safer, cleaner water.

The research, recently published in the journal Angewandte Chemie International Edition, represents a sigificant shift in scientists' understanding of chemistry. Mercury is a serious contaminant so this breakthrough could save millions of pounds.

It is generally accepted that when silver is reduced to nano-sized particles, it can only extract a certain amount of mercury. However, Dr Kseniia Katok, working in the Nanoscience and Nanotechnology Group at the university, was able to reduce the nanoparticles of silver to below 35 nano-metres in diameter (the equivalent of splitting a single human hair into 3,000 separate strands) and found that this allowed almost twice as much mercury to be removed from water.

Dr Kseniia Katok

Dr Kseniia Katok

The team's breakthrough opens the way for more effective, cheaper ways of cleaning mercury-contaminated water. Existing clean-up methods for mercury-polluted water have either low mercury removal capabilities, leave a large chemical waste footprint or are not energy efficient.

Mercury is found naturally in the environment, but levels of inorganic mercury have increased significantly in recent years as a result of industrial processes. When mercury is released in industrial waste and gets into water supplies it can cause devastation to river and sea life as well as gastrointestinal damage and kidney failure to humans who eat contaminated fish.

If this occurs, a hugely expensive decontamination process is required, as occurred in Squamish in Canada where the whole of the waterfront was subject to a huge clean-up starting in the 1990s. The seafront town had been subjected to years of industrial pollution because of its forestry industry which began in the early 20th century. Just the chemicals used to clean the water cost around $50,000,000.

The Brighton scientists say their research shows that using silver nanoparticles would cost a few thousand rather than tens of millions of pounds for the materials, although a device containing the silver nanoparticles capable of processing large quantities of water would need to be developed.

Dr Raymond Whitby, head of the Nanoscience and Nanotechnology Group, said: "The amount of mercury taken into silver nanoparticles defies our current understanding and promises a number of exciting developments. For example, it should lead to improved water treatment, removing greater quantities of selected heavy metals more quickly and perhaps more cheaply than before."

One key element in Dr Katok's discovery is her use of chemically-modified quartz sand, which reduces silver particles to a nanoscale with a high degree of purity. Sergey Mikhalovsky, the university's Professor of Materials Chemistry and Dr Katok's co-supervisor, said: "This is the biggest difference between our silver and that prepared by other commonly-used methods such as citrate reduction, which typically leaves residual chemical groups on the surface of the silver nanoparticles. These can cause unwanted side reactions that may have limited its effectiveness."

He anticipates that modified quartz could be used in other chemical groupings and might, in the future, aid the extraction and decontamination of precious metals such as platinum, palladium and gold.

Andy Cundy, the university's Professor of Applied Geochemistry and Dr Katok's lead supervisor, said: "These findings enable a major shift towards the use of nanomaterials for waste water remediation and metal removal and recycling. We envisage that this composite can cheaply and effectively be incorporated into a variety of configurations to improve water treatment, initially targeting mercury, which remains one of the key environmental contaminants globally."

Hyperstoichiometric Interaction Between Silver and Mercury Redefines Conventional Redox Chemistry at the Nanoscale by Kseniia V. Katok, Raymond L.D. Whitby, Takahiro Fukuda, Toru Maekawa, Igor Bezverkhyy, Sergey V. Mikhalovsky, Andrew B. Cundy has just been published in Angewandte Chemie.

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