Mercury is a common environmental pollutant with well known bioaccumulative
and neurotoxic properties. In the gas phase, elemental mercury has an average
atmospheric residence time of 5.7 years before it is absorbed by aquatic life and enters into the food chain. With estimates that ~2400 tons of mercury per year is currently released to the
atmosphere as a result of human activity, it is in particular a serious threat
to children and pregnant women. According to the US EPA, more than 60,000 babies may be born in the US alone each year at risk of
mercury-related learning and developmental problems because pregnant mothers
either inhale volatile mercury compounds or ate mercury contaminated fish.
Where is all the mercury coming from and what can be done to ultimately stop
A partial answer can be found in the tens of thousands of coal-burning power
stations world wide - and this number is growing rapidly. This multi-trillion
dollar electricity generation industry and other industries such as alumina
refining are the major source of mercury air emissions and are the latest target
of US federal and state clean air regulations. Beginning in 2010, the
cap-and-trade standards are going to impose the total mercury emission from US
power plants to 38 tons annually (a 21% reduction vs. 1999 levels).
researchers have used nanotechnology to create a pioneering sensor that can
precisely measure one of the world's most poisonous substances, mercury. The
mercury sensor developed by RMIT's Industrial Chemistry Group uses nano-engineered gold
structures that attract mercury molecules.
The first step of controlling any kind of toxin (including mercury emissions)
is to be able to measure them, according to Professor Suresh Bhargava, Dean of the School of
Applied Sciences at RMIT University and leader of the Industrial Chemistry
Group. "Traditional mercury sensors can be unreliable because industrial
chimneys release a complex concoction of volatile organic compounds, ammonia and
water vapor, which interfere with their monitoring systems - a significant
challenge to overcome", says Bhargava.
"In order to better understand mercury emission sources, migration, and
environmental and societal impacts of Hg vapor, continuous emissions monitors
(CEMs) located at strategic points within a given process is a must," Bhargava said. Currently, mercury vapor detection is typically
performed, mostly in laboratories, by the use of cold vapor atomic absorption
(CVAA) or atomic fluorescence (CVAF) spectrometry following Hg capturing
Although such spectrometry based systems have excellent mercury detection
capabilities, industries like the alumina and many of the coal fired power
plants are reported to emit high concentrations of Hg vapor in the milligrams
rather than micrograms per cubic meter range. Bhargava goes on to say, "combine this with the complex
concoction of volatile organic compounds, high costs and delicate nature their
incompatibility to function as online CEMs in large industry quickly becomes
Bhargava and his colleagues have tackled this issue head on by
combining the humble quartz crystal microbalance (QCM), a cheap and inexpensive
mass sensitive transducer platforms, with nanotechnology principles. The mercury
sensor was developed with the use of patented electrochemical processes that
enabled the RMIT researchers
to alter the surface of the gold, forming hundreds of tiny nano-spikes, each one
about 1,000 times smaller than the width of a human hair.
Figure 1. Scanning Electron Micrographs of pure gold
surface electro-deposited with gold nanospikes imaged at 0 seconds, 15 seconds,
90 seconds and 150 seconds (clockwise), illustrating the nucleation and
nanostructural growth formation in time. Scale bar is 500 nm
- 1nm (nano meter) is 10-9 meters or 1 billionth of a meter).
Part of the research published earlier this year in Sensors and Actuators B:
Chemical journal indicated that mercury affinity could be increased by forming a
surface with an increased number of active sites. "We've known since ancient
times that gold attracts mercury, and vice versa, but a regular gold surface
doesn't absorb much vapor and any measurements it makes are inconsistent," Professor Bhargava said. "Our nano-engineered gold surfaces
are 180 per cent more sensitive than non-modified surfaces when operating at
89°C". "They're finely targeted, so they're unaffected by the usual gases found
in effluent gas streams and the sensors we've created using those
nano-engineered surfaces have worked successfully at a range of extreme
temperatures over many months, just as they'll need to in an industrial
Figure 2. Coloured Scanning Electron
Micrograph of 150 second electro-deposited gold. Scale bar 500nm. (Image
processed colour applied).
The breakthrough is attributed to nano-engineered gold surfaces having a
higher affinity for Hg, and "not solely due to increased surface area effects,"
says Bhargava. His teams results indicate that mercury adsorption
on gold varies substantially for different morphologies. The developed
nano-spike surfaces retained their affinity for longer periods (time) and large
number of Hg monolayer coverage, while decreasing the influence of the
contaminant gases present in the industrial effluent streams.
Figure 3. Coloured Scanning Electron
Micrograph of evaporated gold thin film before electro-deposition. Scale bar
500nm (Image processed colour applied).
Funded through an Australian Research Council Linkage grant, the project was
supported by leading industry partners, who have now engaged RMIT to develop a mercury
sensing device for a pilot plant trial at one of their Australian
Mercury in the Environment: Its Sources and its
Mercury Emissions from Electric Power Plants: An Analysis of EPA's
U.S. Company Schemes to Dump Used Mercury in India
Funding struggle for mercury monitoring
Nano mercury monitoring
Mercury Rising - Up the Food Web
Wanted: Home for 17,000 tons of mercury
Copyright AZoNano.com, Professor Suresh Bhargava
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