Navalon, S, M de Miguel, R Martin, M Alvaro and H Garcia. 2011. Enhancement of the catalytic activity of supported gold nanoparticles for the fenton reaction by light. Journal of the American Chemical Society http://dx.doi.org/10.1021/ja108816p.
Just about everything – from cars to laptops to cells to chemical reactions – needs energy to start up and keep going. Now, chemists in Spain have stumbled on a way to use light – the simplest and most abundant energy source – to speed up reactions that may be used to degrade a water pollutant, phenol.
The results suggest light can drive a chemical reaction that uses minute quantities of gold, titanium and oxygenated water to degrade a chemical pollutant known as phenol. They report the results of their laboratory study in the Journal of the American Chemical Society.
Phenol is a contaminant in industrial effluents and municipal sewage that is commonly found in rivers and lakes. It can occur naturally, but the bulk of it in waterways is produced from making resins for plastics and the building industry, nylon fabric and medicines. Phenol is an essential building block to make bisphenol A, a plasticizer that is widely used in the resins that line food and drink cans. Phenols are also used in medicines and personal care products, such as ointments, mouthwash and throat lozenges.
People are exposed to phenols by eating or breathing them at work or through medicines. Phenols can irritate skin and extended exposure to high levels can lead to loss of appetite, nervous system problems and cardiovascular conditions.
In this study, researchers showed that light could help gold nanoparticles drive a new kind of chemical reaction. The breakthrough may be a very applicable solution to a common problem of cleaning up contaminated water in streams, rivers and lakes.
Making and destroying a molecule takes energy. So using the sun as a source is a good idea. After all, plants build and maintain themselves using sunlight as unique energy source
Already a large number of light-promoted chemical reactions are at play in consumer products. For instance, some windowpanes used in large buildings have a self-cleaning technology. Very small pieces of a material called titania cover the surface of the glass. Titania can harvest UV light from the sun and break the pollutants that adhere to their surface down into carbon dioxide and water. But using sunlight to make reactions go still has limitations. Water treatments remain a challenge.
In this study, Hermenegildo Garcia and his group deposited gold nanoparticles onto small pieces of diamond. They added a mixture of a pollutant – phenol – and hydrogen peroxide – best known as oxygenated water – onto the materials. Then, they exposed the mixture to light and they observed degradation of phenol.
Normally, hydrogen peroxide is powerful enough to break phenol down. But, in the presence of the gold and diamond material and light, they saw something quite amazing. The reaction was up to 10 times faster. They also found that the more light was shed on the mixture, the faster the reaction. This proves the central role of light in this new process. The reaction proceeded using either laser light or sunlight.
They discovered even more. Phenol degradation requires very acidic conditions, usually uncommon in streams and other waterways. In the lab, under dark and neutral pH – non-acidic – conditions, no reactions occurred. But, again, as soon as light was shed on the mixture, the particles degraded phenol and it disappeared. The products of degradation of phenol are not discussed in the report.
More studies are needed to show the process can work outside of laboratory conditions. Challenges include studying the gold containing materials’ resistance to natural conditions and figuring out how to expose the particles evenly to light in the cleaning unit. However this research shows promise in developing strategies to clean up polluted water.
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