To treat water… researchers shed light (with laser) on a new technology

For water treatment… Researchers shed light (with laser) on a new technology

Ensuring a growing global population has access to clean water will require new ways to treat water. One of these next-generation methods involves a form of iron known as tetravalent iron, which produces fewer toxic byproducts than chemicals like chlorine and is potentially cheaper and easier to use than ozone water treatment systems.

For this form of iron to work best, it must be combined with other compounds, or stimulated with light energy. Now using a technique involving laser pulses and ultra-fast X-rays, a team of University of Rhode Island researchers has revealed new details about the chemical reaction that occurs when this type of iron is exposed to visible and ultraviolet light. The results, which were published in the Journal of the American Chemical Society, could help researchers improve the use of this substance in water treatment applications.Water treatment.

Photoactivation of iron ions

Dugan Hayes, assistant professor of chemistry at the University of Rhode Island and the author responsible for the study, said: “The mechanisms of photoactivation have never been researched in depth, but in this study we were able to reveal some of those photophysical properties for the first time.”

Ferrate is an oxidizing substance, which means that it can break down pollutants by gaining their electrons. This substance alone is considered a fairly strong oxidizing substance, but when it is activated with light, there is a more powerful oxidizing substance that is pentavalent iron ions. Before this new study, it was not known how much energy would be required to produce pentameric iron, and in what quantities it could be produced.

To find answers to these questions, Hays Lab doctoral student Calle Antolini led experiments using transient absorption spectroscopy, a technique that investigates photochemical reactions using ultrafast laser pulses. The initial pulse starts the reaction, while subsequent pulses explore the steps of the reaction as it works. The speed of the pulses, on the order of a few millionths of a second, gives researchers a detailed record of even the shortest-lived reaction products.

Antolini conducted experiments using pulses of ultraviolet and visible light using instruments at the University of Rhode Island, and similar experiments were conducted using X-rays at Argonne National Laboratory in Chicago, where Antolini works as part of the US Department of Energy’s Student Research Program.

Development of water treatment systems

The work showed that the conversion rate from iron quaternary to highly reactive iron pentose was about 15%, a rate comparable to that of ozone purification systems. The research also showed surprising results regarding the type of light needed to produce the most reactive iron species. The team found that a range of wavelengths of light extending from almost the ultraviolet to visible spectra should be able to produce pentameric iron.  The researchers say this discovery is important for two reasons: first, visible light uses less energy to produce ultraviolet light; This may make this method more energy efficient than previously assumed. In addition, visible light is scattered less in turbid water, meaning pentameric iron can be produced in a variety of water conditions.

The results are encouraging for Joseph Goodwill, assistant professor of civil and environmental engineering at Rhode Island and co-author of the study. Part of his research program is to find ways to close the “clean water gap” between larger urban water treatment systems and smaller rural systems.

Goodwill says: “Purification systems based on iron ions are a promising option for smaller systems, where expensive and complex ozone systems are not practical.” Ferrate also has the ability to reduce reliance on harsh chemicals like chlorine, and may also eliminate stubborn contaminants that chlorine cannot remove. These substances include fluorosurfactants, a class of chemicals increasingly found in wells and water systems, but before systems based on iron quaternary ions can be widely deployed, scientists need to better understand the chemistry of this substance.”

He added: “It has been difficult for us to understand how strong oxidants are formed mechanically from iron quaternary ions, and this has hindered process improvement and comprehensive implementation in water treatment applications, but the results presented in this research paper improve our basic understanding of the iron quaternary system, which will open the doors to a number of applications.”

Researchers hope that these new findings on how photochemistry works with iron will help expand the use of water treatment systems based on iron ions.