Clean water is becoming a major resource utilization problem that is increasingly attracting worldwide attention. In order to ensure that the growing global population has access to clean water, the development of new water treatment methods has also been put on the agenda.
You may not think that when a kind of iron called ferrate is exposed to special light (laser) and a series of chemical reactions occur, it may become a blessing of water treatment technology. It is reported that ferrate produces fewer toxic by-products than chlorine and other chemicals, and may be cheaper and easier to deploy than complex ozone treatment systems.
The thorny problem of this new treatment method is that it needs to be combined with other compounds or excited by light energy to make ferrate play the best role in water disinfection and purification.
Recently, a group of researchers from the University of Rhode Island (URI) in the United States used a technology involving ultra high speed laser and X-ray pulse to reveal new details of ferrate chemical reaction when exposed to visible light and ultraviolet light. Relevant research results published in the Journal of the American Chemical Society (JACS) can help researchers optimize their application in water treatment.
Dugan Hayes, assistant professor of chemistry at the University of Rhode Island and the corresponding author of the study, said that the light activation of ferrates had never been studied in detail before, and their team revealed some of the photophysical properties for the first time in this study.
Ferrate is an oxidant, which means it can "steal" electrons from pollutants to decompose them. Ferrate itself is a fairly strong oxidant, but when excited by light, it will produce a stronger oxidant, called Fe (V) (or Fe5+). However, before this new study, people did not know how much energy is needed to produce Fe (V) and how much energy can be produced.
In order to clarify these aspects, Cali Antolini, a doctoral student in Dugan Hayes Laboratory, led a transient absorption spectrum experiment, which is actually a technology to study photochemical reactions using ultrahigh speed laser pulses.
Cali Antolini conducted experiments using ultraviolet and visible light pulses at the facilities of the University of Rhode Island. In addition, she also conducted similar experiments with X-ray on the advanced photon source large synchrotron platform of Argonne National Laboratory in Chicago.
In this experiment, the initial pulse is responsible for initiating the reaction, and the subsequent pulse is responsible for detecting the reaction process. The speed of laser pulse is about one billionth of a second, which allows researchers to record the reaction products in detail even in the shortest time.
The results showed that the conversion of ferrate to highly active Fe (V) was about 15%. This study also found that a series of wavelengths extending from the ultraviolet spectrum to the visible spectrum should be able to produce Fe (V).
The researchers said that there are two reasons for this important discovery: first, visible light requires less energy to generate ultraviolet light, which makes the energy efficiency of ferrate excitation higher than previously assumed. In addition, visible light scatters less in turbid water, which means that Fe (V) can be produced under various water conditions.
The study also helps to find a way to bridge the "clean water gap" between large urban water treatment systems and small rural water treatment systems. The construction of ferrate purification system is smaller and cheaper. Compared with expensive and complex ozone treatment system, the practicability is expected to be improved. In addition, ferrate is also expected to reduce dependence on irritant chemicals such as chlorine, and may even eliminate stubborn pollutants that cannot be removed by chlorine, including perfluoro/polyfluoroalkyl substances (PFAS), which are more and more common in water systems across the United States. But before ferrate system is widely used, scientists need to better understand the chemical properties of ferrate.
Joseph Goodwill, co-author of the study and assistant professor of civil and environmental engineering at the University of Rhode Island, said: "It is difficult to understand the formation of strong oxidants in ferrates from the mechanism, which hinders the process optimization and comprehensive implementation of water treatment applications. The conclusions drawn in this paper improve our basic understanding of ferrate systems and open the door for this application."
The researchers hope that these new discoveries on the working principle of ferrate photochemistry will help expand the use of iron based water treatment. At present, this research has been supported by the US Department of Energy (DE-SC0019429 and DE-AC02-06CH11357) and the US National Science Foundation (2046383).
Source: OFweek
