By Petronilo Morin IV
Chromium – Looks great on vehicles but not in our
environment. In water, chromium is mainly found as Cr(VI) and is toxic at even
low concentrations, with the EPA placing a maximum safety threshold of 100 ppb
in drinking water. Chromium is a transition metal with strong oxidizing power
and is used in industry for various reasons, but its excess careless use has
polluted bodies of water leaving organisms to deal with this dangerous element.
So, the demand of efficient removal of this toxic species from ground water is rising.
Current techniques for removal of Cr(VI) ions from drinking water are
inefficient and have many drawbacks. They either are expensive, have slow
kinetics, result in incomplete removal of the toxic metal, or impractical.
Fortunately, scientists at the Oak Ridge National
Laboratory have synthesized a Covalent Organic Framework (COF) for efficient
removal of Cr(VI) from water (Jansone-Popova et al., 2018). Specially, these
COF are guanidinium-based because guanidinium functional groups ionically bind with
a variety of oxoanions, including Cr(VI). The ability of these novel COFs in this study have resulted in rapid removal of Cr(VI)
ions in water with unprecedented selectivity that ranges from 90 – 200 mg/g.
Moreover, based on the pH of the solution, this reduction of Cr(VI)
concentration can happen in just minutes.
Success in removal of Cr(VI) could potentially
provide a principle design to remove similar toxic metals such as arsenate from
groundwater. However, within the COFs, Cr(VI) is reduced to Cr(III) and the
guanidinium is converted to neutral guanidine. What happens with the excess
byproducts of this process could become a new concern itself.
Below shows the general mechanism of the aforementioned COFs.
In summation, the novel synthesis of the
guanidinium-based COF by the scientists at the Oak Ridge National Laboratory
not only gives hope that we all can have safe drinking water but also the
sustainability of our natural capital. In this world, even though people are
separated by many things, one thing we all share is Earth.
Reference
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