Graduate student Honghan Fei holds a sample of SLUG-26, a new material developed by Fei and chemist Scott Oliver. Photos: T. Stephens.
Water softening techniques are very effective for removing
minerals such as calcium and magnesium, which occur as positively-charged ions
in “hard” water. But many heavy metals and other inorganic pollutants
form negatively charged ions in water, and existing water treatment processes
to remove them are inefficient and expensive.
Chemists at the University
of California, Santa Cruz, have now developed a new type of
material that can soak up negatively charged pollutants from water. The new
material, which they call SLUG-26, could be used to treat polluted water
through an ion exchange process similar to water softening. In a water
softener, sodium ions weakly attached to a negatively-charged resin are
exchanged for the hard-water minerals, which are held more tightly by the resin.
SLUG-26 provides a positively charged substrate that can exchange a nontoxic negative
ion for the negatively charged pollutants.
“Our goal for the past 12 years has been to make
materials that can trap pollutants, and we finally got what we wanted. The data
show that the exchange process works,” says Scott Oliver, associate
professor of chemistry at UC Santa Cruz.
The chemical name for SLUG-26 is copper hydroxide
ethanedisulfonate. It has a layered structure of positively charged 2D
sheets with a high capacity for holding onto negative ions. Oliver and UCSC
graduate student Honghan Fei described the compound in a paper that will be
published in Angewandte Chemie.
The researchers are currently focusing on the use of SLUG-26
to trap the radioactive metal technetium, which is a major concern for
long-term disposal of radioactive waste. Technetium is produced in nuclear
reactors and has a long half-life of 212,000 years. It forms the negative ion
pertechnetate in water and can leach out of solid waste, making groundwater
contamination a serious concern.
“It’s a problem because of its environmental mobility,
so they need new ways to trap it,” Oliver says.
In their initial studies, the researchers used manganese,
which forms the negative ion permanganate, as a non-radioactive analog for
technetium and pertechnetate. The next step will be to work with technetium and
see if SLUG-26 performs as effectively as it did in the initial studies.
“Whether or not it can be used in the real world is
still to be seen, but so far it looks very promising,” Oliver says.