Super Sand & Cactus Gum (GlycoProtein)
BY ARIEL SCHWARTZ Jun 28, 2011
Sand is a cheap and easy to find water filter. It's also not a very good water filter. But a new development--coating sand in graphite--could make it possible for everyone in the world to have easy access to clean water.
Nearly one billion people lack access to safe drinking water. There are creative ways to purify dirty water when a Brita isn't handy, to be sure--people living in areas with plentiful sand, for example, can pour water through sand and pebble-filled filters. But while the sand quickly filters water and removes large particles, it is, not surprisingly, ineffective at removing heavy metals, pathogens, and other toxins that find their way into dirty water.
A newly developed "coated sand," uses graphite oxide--a substance used in the chemical process for making pencil lead (or graphite)--to filter out the contaminants that regular sand can't touch. It could be cheap to produce and almost as plentiful as plain old sand.
When Rice University researchers ran two model contaminants (mercury and Rhodamine B dye) through the super sand, they found that the coated substance removed contaminants as well as commercially available active carbon filtration systems. The big difference: The super sand is cheap. Graphite is inexpensive (waste graphite from mining operations could even be used), and the coating process can occur at room temperature.
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.
Coated sand could, in other words, be at least one solution to our growing water crisis--along with cactus gum, the Tata Swach, and fog-harvesting devices.
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