'Super sand' for better purification of drinking water (Update)

Jun 23, 2011

(PhysOrg.com) -- Scientists have developed a way to transform ordinary sand -- a mainstay filter material used to purify drinking water throughout the world -- into a "super sand" with five times the filtering capacity of regular sand. The new material could be a low-cost boon for developing countries, where more than a billion people lack clean drinking water, according to the report in the ACS journal Applied Materials & Interfaces.

Researchers at Rice University are spinning a bit of nano-based magic to create "coated sand" that has enhanced properties for water purification. The breakthrough may benefit where more than a billion people lack .

Beds of sand are commonly used throughout the world to filter . The particle size of sand and surface modifications determine the efficiency of sand in removing contaminants from water.

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Beds of sand are commonly used throughout the world to filter drinking water. The particle size of sand and surface modifications determine the efficiency of sand in removing contaminants from water. Researchers at Rice University are spinning a bit of nano-based magic to created "coated sand" that has enhanced properties for purification. The breakthrough may benefit developing countries where more than a billion people lack clean drinking water.

The Rice researchers’ technique makes use of graphite oxide, a product in the chemical exfoliation process of graphite (aka pencil lead) that leads to single-atom sheets known as graphene via subsequent reduction.
A team from the Rice lab of Professor Pulickel Ajayan published a report in the American Chemical Society journal and Interfaces describing a process to coat coarse grains of sand in graphite oxide; the resulting material is several times more efficient at removing contaminants than sand alone.

Nanosheets of graphite oxide can be tailored to have hydrophobic (water-hating) and hydrophilic (water-loving) properties. When mixed in a solution with sand, they self-assemble into coatings around the grains and keep the hydrophilic parts exposed. Adding aromatic thiol molecules to the coatings enhances their ability to sequester water-soluble contaminants.

Ajayan, a Rice professor in mechanical engineering and materials science and of chemistry, and his collaborators from Australia and Georgia conducted experiments to compare this coated sand with plain sand and activated carbon granules used by municipalities and in-home systems.

Beakers of solution containing mercury and Rhodamine B dye await purification through a new process developed at Rice University. (Credit: Jeff Fitlow/Rice University)

The researchers ran two model contaminants -- mercury (at 400 parts per billion) and Rhodamine B dye (10 parts per million) -- through sand and coated sand placed into filtration columns. They found coarse sand's adsorption capacity of mercury was saturated within 10 minutes.

The coated sand continued removing mercury for more than 50 minutes and resulted in filtered water with less than one part per billion. (The Environmental Protection Agency's maximum contaminant level goal for mercury in drinking water is two parts per billion.)

Results for water treated with Rhodamine B dye were similar.

The researchers found coated sequestered contaminants just as well as the commercially available active carbon filtration systems they tested.

The lab is looking at ways to further functionalize graphite oxide shells to enhance contaminant removal. "By attaching different functional moieties onto graphite oxide, we could engineer some form of a 'super sand' to target specific contaminants species, like arsenic, trichloroethylene and others," said Rice graduate student Wei Gao, primary author of the paper.

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More information: "Engineered Graphite Oxide Materials for Application in Water Purification" ACS Appl. Mater. Interfaces, 2011, 3 (6), pp 1821–1826
DOI: 10.1021/am200300u

Abstract
Retaining the inherent hydrophilic character of GO (graphite-oxide) nanosheets, sp2 domains on GO are covalently modified with thiol groups by diazonium chemistry. The surface modified GO adsorbs 6-fold higher concentration of aqueous mercuric ions than the unmodified GO. “Core–shell” adsorbent granules, readily useable in filtration columns, are synthesized by assembling aqueous GO over sand granules. The nanostructured GO-coated sand retains at least 5-fold higher concentration of heavy metal and organic dye than pure sand. The research results could open avenues for developing low-cost water purification materials for the developing economies.

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that_guy
5 / 5 (2) Jun 22, 2011
but...I'd like to know how how much cheaper it would be to coat sand with nanographite oxide than it would be just to give poor people activated carbon...and how it would compare with say...a mix of sand and activated carbon.
gmurphy
5 / 5 (2) Jun 23, 2011
what on earth can't graphene be used for?, we'll be stirring it into our tea next :)
Royale
1 / 5 (1) Jun 24, 2011
My only guess is thinking ahead and saving on our coal deposits, by using just a bit of it and sand (which there is plenty of all over). I guess it could only save money if you could make an easy low power consuming process to create it; otherwise you'd just be burning the coal for the power required to make the nano-carbon-sand.
emsquared
not rated yet Jun 24, 2011
I guess it could only save money if you could make an easy low power consuming process to create it; otherwise you'd just be burning the coal for the power required to make the nano-carbon-sand.

It sounded like the graphite oxide is a by-product of another process ("the chemical exfoliation process of graphite") so it's not like it'd be a devoted production. And if it's a process that is gonna be conducted anyway and it's something that was formerly waste and can now be re-purposed, can't complain about that, no? I would hope the "low-cost boon" statement would mean it can be made cheaper than present filtration products.
Dug
not rated yet Jun 27, 2011
Once again an author fails to cover his subject adequately. All filtration technology necessarily has two modes - attraction/capture and then the purposeful release of attached contaminants. If the graphite oxide coating doesn't effectively release contaminants, then it's essentially a waste of time. Why wasn't this info in the article?
Royale
not rated yet Jun 28, 2011
Dug, why would they need to be reusable? Sure it would be great if the were, but activated carbon filters aren't now and they still work well. So if we could reduce the amount of carbon used by adding some desert, why not?
that_guy
not rated yet Jun 28, 2011
My only guess is thinking ahead and saving on our coal deposits, by using just a bit of it and sand (which there is plenty of all over). I guess it could only save money if you could make an easy low power consuming process to create it; otherwise you'd just be burning the coal for the power required to make the nano-carbon-sand.

I kind of want to be mean to you, but I'll refrain. Activated charcoal is commonly made from coconut husks or wood. It is not made from coal. There is coal in abundance compared to any other fossil fuel, and the only concern about coal in almost any scenario is environmental.
Royale
not rated yet Jun 29, 2011
Sure that_guy. You're right, no need to be mean. Saying coal supply like that would make it seem that that's the only way I thought it could be made. And that is simply wrong. So sorry for my un-clearness. We do not need coal to make activated charcoal, just something carbon based that is sufficiently burned will do the trick. My only question with this whole thing is do the benefits of this new process outweigh the strain? As of now, probably no. But perhaps the process can be made simpler and it would be great to be able to make this product cheap and on a mass scale. Then we won't have to burn coconut husks to fill our shoes to take the stink out, we'd then just need add this special 'sand' to an Odor Eaters.