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Coatings researchers in Texas and Australia are touting a new coating that transforms ordinary sand–a mainstay filter material used to purify drinking water worldwide–into a “super sand” with five times the filtering capacity.
“Engineered Graphite Oxide Materials for Application in Water Purification,” in the American Chemical Society journal ACS Applied Materials & Interfaces, describes the work by scientists at Rice University in Texas and Monash University in Australia.
Low-Cost Filtration
The new material could be a low-cost option for developing countries, where more than a billion people lack clean drinking water, reports the team, led by Dr. Mainak Majumder of Monash’s Nanoscale Science and Engineering Laboratory.
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| Dr. Mainak Majumder is using a nanomaterial called graphite oxide to improve filtration. |
The authors note that sand has been used to purify water for more than 6,000 years, and that sand or gravel water filtration have been endorsed by the World Health Organization. Their studies of a nanomaterial called graphite oxide (GO) suggest that it could be used to improve sand filtration in a cost-effective way, they say.
Coating Restructured
The researchers used a simple method to coat sand grains with graphite oxide, creating a “super sand” that successfully removed mercury and a dye molecule from water.
The team changed the structure of graphite, the soft carbon-black substance found in pencils, to dramatically increase its surface area before coating the grains of sand with it. This, in turn, increased the sand’s surface area and, thus, its ability to filter contaminants, the scientists said.
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| Researchers restructured the graphite oxide to dramatically increase its surface area. |
In the mercury test, ordinary sand was saturated within 10 minutes of filtration, while the super sand absorbed the heavy metal for more than 50 minutes, the scientists found. That level of filtration performance “is comparable to some commercially available activated carbon,” without the extremely high temperatures required for that process, the scientists said.
Similarly, the coated sand absorbed dyed water for 100 minutes, compared with just 20 minutes for uncoated sand.
Reusing Waste Products
“The beauty of this process is that we have the structural function of sand with the functionality of the nano-carbon material and everything is done at room temperature,” Majumder said.
“Another important aspect is that the fine graphite we use is a waste product from graphite mining. It is also available relatively cheaply in Australia, which has some of the world’s largest quantities of base-grade graphite deposits.”
The team is now investigating strategies that will enable them to assemble functionalized GO particles on the sand grains to further enhance contaminant removal efficiencies.
The research was underwritten by a nanotech research firm called Nanoholdings LLC, of Rowayton, CT. The company has research affiliations with Rice and five other universities around the world.
Researchers have applied for a patent on the process.
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