Krista D. Zanolli, email@example.com
URBANA-CHAMPAIGN, Ill. – Ultraviolet water purifiers have been on the market for years and have gained popularity among
those looking for a chemical-free, more natural approach to clean drinking water.
Now researchers at the University of Illinois have improved on
the process by using visible, rather than UV, light. What’s more, the new
process works even after the light is turned off – disinfecting in the dark.
Based on a new photocatalyst, the process also can be used to
sanitize surgical equipment and to clean delicate electrical and optical components.
“The new catalyst also has a unique catalytic memory effect
that continues to kill deadly pathogens for up to 24 hours after the light is turned
off,” said Jian-Ku Shang, a professor of materials science and engineering
at the university.
Jian-Ku Shang, a professor of materials science and engineering at
the University of Illinois, holds a sample of a new photocatalytic material that
uses visible light to destroy harmful bacteria and viruses, even in the dark. Courtesy
of L. Brian Stauffer.
In earlier research, he and his group developed a catalytic material
that works with visible light by doping a titanium-oxide matrix with nitrogen, enabling
the disinfecting process to be activated by sunlight or by standard indoor lighting.
“When visible light strikes this catalyst, electron-hole
pairs are produced in the matrix,” Shang said. “Many of these electrons
and holes quickly recombine, however, severely limiting the effectiveness of the
Damage to E. coli cells by the photocatalytic process is shown. Courtesy
of Jian-Ku Shang.
Alone, the nitrogen-doped titanium oxide kills bacteria, but not
very efficiently. To create the catalytic memory, the researchers added nanoparticles
of palladium to the surface of the fibers so that, when the light is turned off,
the nanoparticles slowly release the trapped electrons, which then react with water
to produce additional oxidizing agents.
They tested the process using a metal halogen desk lamp and a
solution of Escherichia coli. A glass filter on the lamp provided zero light intensity
below 400 nm. They shone the light on the fibers for 10 hours to simulate daylight
and stored them in a dark environment for various periods.
“In a sense, the material remembers that it was radiated
with light,” Shang said. “This ‘memory effect’ can last
up to 24 hours.”
Even though the disinfection efficiency in the dark is not as
high as it is in visible light, it still enables continuous operation of the process,
which Shang suggests could lend itself to environmental applications.
Shown is a schematic of the process in which photoelectrons flow to
palladium-oxide (PdO) nanoparticles on a titanium-oxide (TiON) matrix
under visible light illumination and the process of discharging of PdO
when the visible light is switched off. (Note that A refers to an
that can accept surface photoelectrons, while D refers to an electron
can donate electrons and react with surface holes.) Courtesy of Qi Li,
Yin Wai Li,
Zhiquan Liu, Rongcai Xie and Jian-Ku Shang, J Mat Chem, 2010, Vol. 20,
1068-1072, DOI: 10.1039/b917239d – Reproduced by permission of the Royal
“In the near term, we are exploring applications of this
technology in two areas – disinfecting municipal water and building point-of-use
devices for purifying drinking water,” he said. “For the long term,
we are interested in understanding the mechanism underlying the catalytic memory
effect, designing new materials with even stronger memory effect and using the materials
for control of infectious diseases.”
The work was supported by the National Science Foundation through
the university’s Center of Advanced Materials for the Purification of Water
with Systems. Some of the work was performed at the university’s Frederick
Seitz Materials Research Laboratory, which is partially supported by the US Department