team of researchers at the U.S. Department of Energy’s Ames Laboratory has
answered a key question concerning the widely used Fenton reaction—important in
wastewater treatment to destroy hazardous organic chemicals and decontaminate
bacterial pathogens and in industrial chemical production. The naturally
occurring reaction was first discovered in 1894 by H.J.H. Fenton, a British
chemist at Cambridge, and involves hydrogen peroxide and iron.
the Fenton reaction actually happens has remained in contention. Scientists
have long debated whether it was a hydroxyl (OH) radical or a form of iron known
as the ferryl ion that functioned as the reaction intermediate for the Fenton
reaction, with data to support both theories.
Andreja Bakac and Oleg Pestovsky, scientists at Ames Laboratory in the Division
of Chemical and Biological Sciences, and chemistry graduate student Hajem
Bataineh, have proved that the reaction can take different paths depending on
the pH of the reaction environment. In an acidic environment, the intermediate
is a hydroxyl radical; at neutral pH, the intermediate is the ferryl ion.
is enormous when you think about all the work that went into trying to solve this
issue when the acidity of the solution was not considered as a parameter. It
certainly varied from one work to the next, and may explain the confusion that
grew out of contradicting results in the literature,” says Bakac.
is the reaction fundamental? Yes. Simple? No. The exact nature of the mechanism
of the Fenton reaction has eluded science for decades, and has been all that
time a subject of close inquiry—and debate.
reaction takes place between iron which is widespread on Earth, and hydrogen
peroxide which is derived from oxygen and also present almost everywhere on
this planet. You know you are facing a real challenge when the reaction between
two very common compounds has not been fully explained in a hundred years,
despite all the efforts,” says Bakac.
those past hundred years, the Fenton intermediates were reduced to two, the
hydroxyl radical or the ferryl ion.
was known already about hydroxyl radicals. However, it wasn’t until 2005 that
Bakac’s research group, in collaboration with groups at Carnegie Mellon and
University of Minnesota, was able to directly characterize the ferryl ion and
study its reactions. This gave them the ability to compare the two potential
found that these two species, in many of the reactions, behave pretty much the
same, which would make it very difficult to distinguish between them,” explains
Bakac of the earlier research. The breakthrough came with some unique reactions
that one intermediate will do and the other one will not, or where the products
were different, and that gave us the key.
were thrilled to obtain a clear and unambiguous answer. The intermediate was
the OH radical, and not the ferryl ion. We published the paper, we had a write
up in Chemical and Engineering News;
this was very exciting.”
the question still didn’t seem settled. Other scientists continued to assert
that ferryl was the intermediate.
thought how can this be? We just proved that it isn’t. There were also some
theoretical papers that came out at the time, also supporting the ferryl ion.”
continued debate prompted Bakac and her research partners to look at the
potential effect of reaction conditions, specifically the acidity of the
solution. That led to the discovery that either intermediate can be involved,
depending on the pH of the reaction environment.
discovery not only solves a long-running debate in academic chemistry, it opens
up possibilities for new ways to use the reaction.
we can understand fully what’s going on, then we can take advantage of that
understanding and develop new uses for the Fenton reaction,” says Bakac.
discovery could lead to catalytic reactions using widely available iron in
neutral conditions, and environmentally friendlier processes in everything from
wastewater treatment to industrial oxidations.
becomes not just a better understood reaction, but a more useful one from a
practical standpoint,” says Bakac.
findings were published in Chemical
Source: Ames Laboratory