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Trapped sunlight cleans water


January 24, 2011
By American Institute of Physics (AIP)

January 21, 2011 –
High-energy costs are one drawback of making clean water from waste effluents. According to an article in
the journal Biomicrofluidics, published by the American Institute of Physics, a
new system that combines two different technologies proposes to break down
contaminants using the cheapest possible energy source, sunlight. Microfluidics
– transporting water through tiny channels – and photocatalysis – using light
to break down impurities – come together in the science of optofluidics.

January 21, 2011 –
High-energy costs are one drawback of making clean water from waste effluents. According to an article in
the journal Biomicrofluidics, published by the American Institute of Physics, a
new system that combines two different technologies proposes to break down
contaminants using the cheapest possible energy source, sunlight. Microfluidics
– transporting water through tiny channels – and photocatalysis – using light
to break down impurities – come together in the science of optofluidics.

“These two technologies
have been developed in parallel but there have been few efforts to employ the
natural synergy between them,” says author Xuming Zhang of the Hong Kong
Polytechnic University
. “Our results showed a dramatic improvement in the
efficiency of the photocatalyst.”

The researchers fabricated
a planar microfluidic reactor, or microreactor, which is essentially a
rectangular chamber made of two glass plates coated with titanium dioxide, the
active ingredient in many sunscreen lotions. On exposure to sunlight, the
coating releases electrons that react with contaminants in the water and break
them down into harmless substances. This is the photocatalysis part of the
process. The high surface area of the microreactor enhances the ability of the
catalyst to capture sunlight. Although the gap between plates is small, Zhang
plans to expand the rectangular dimensions to two square meters.

“Our current small-scale
proves the concept but we are also scaling up the reactor to a throughput of
1,000 liter per hour,” he says.

If the larger reactor
proves effective, many parallel devices might be used to handle industrial
water treatment applications.

The article,
"Optofluidic planar reactors for photocatalytic water treatment using
solar energy" by Lei Lei, Ning Wang, Xuming Zhang, Qidong Tai, Din Ping
Tsai, and Helen L. Chan appears in the journal Biomicrofluidics. See:
http://link.aip.org/link/biomgb/v4/i4/p043004/s1.


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