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Purifying Our Rivers With a Bit of Rare Earth

Scientists from the Indian Institute of Science have found a remarkable way to degrade microbes and chemical dyes polluting our rivers. All you need to do is take the material and suspend it in water in sunlight! Moreover, it is reusable.

This research has resulted in a new ‘nano composite material’ containing one of the rare earth elements, Cerium. “Environmental pollution causes serious hazards to human health. Chemical effluents and toxic wastes are discarded into the natural systems without any treatment. Therefore, industrial effluents and wastewater contaminants must be monitored and treated,” mentions Neerugatti Krishna Rao Eswar, an author of the paper.

To tackle this issue, the team of researchers has come up with a new material that facilitates the formation of hydrogen peroxide in water, when exposed to visible light. The material uses the process of photocatalysis -- the acceleration of a chemical reaction that takes place in light, in the presence of a catalyst. The hydrogen peroxide formed is a very strong oxidising agent, which results in the breakdown of dyes and bacteria.

This catalyst has been rigorously tested with chemical dyes and the bacterium Escherichia coli, and has been found to degrade a large fraction of both within an hour. All it takes for the catalyst to work is to be suspended in water in sunlight.

Ceria, an inexpensive oxide of the rare earth element Cerium, is used as a UV-blocking and shielding agent because it can absorb light in the ultraviolet region. Cerium is a rare earth element found in the Lanthanides section in the periodic table. It is a soft, silvery, ductile metal which easily oxidizes in air and resembles Iron in its mechanical properties.

“Based on the confinement effects, it was shown that ceria can absorb visible light,” says Eswar. This means that if ceria is part of a composite material, its electronic configuration changes so that it absorbs visible light instead of ultraviolet light.

In their study, the investigators found that ceria nanoflakes could be combined with silver bromide and silver phosphate to create a reusable nano-composite catalyst. Using techniques like X-ray diffraction analysis, diffuse reflectance spectroscopy, electron microscopy, BET surface area analysis, and X-ray photoelectron spectroscopy, the authors have been able to elucidate the reasons for the success of the composite.

“The superior photocatalytic activity of this nano-composite for the degradation chemical dyes is attributed to its extended absorption in visible region and enhanced stability of the catalyst owing to the firm adherence of silver bromide and phosphate to ceria nanoflakes,” notes Eswar.

About the authors:

Neerugatti KrishnaRao Eswar, is a PhD researcher in the Centre for Nanoscience and Engineering, IISc. Venktesh V. Katkar is an undergraduate student from the Visvesvaraya National Institute of Technology who did his summer intership in IISc. Prof. Praveen C. Ramamurthy is an Assistant Professor in the Department of Materials Engineering, IISc. Prof. Giridhar Madras is a Professor in the Department of Chemical Engineering, Indian Institute of Science.

Contact: Prof Giridhar Madras giridhar@chemeng.iisc.ernet.in

This paper appeared in the Journal of Industrial and Engineering Chemistry Research in the August of this year.

http://pubs.acs.org/doi/abs/10.1021/acs.iecr.5b01993