Porous Gel Purges Water of Dangerous Pathogens

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Wednesday, August 28th, 2013
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Spongy Material Puts Squeeze Waterborne
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Environmental engineers have developed a porous gel riddled with silver nanoparticles which is capable of creating potable water swiftly and conveniently by killing off hazardous pathogens.

The gel was created by a team of material scientists and environmental engineers from both Singapore and the United States who were prompted to pursue its development through reports of the difficulty that survivors of the 2004 Indian Ocean Tsunami experienced in obtaining clean, potable water immediately following the disaster.

The porous gel works by using silver nanoparticles to kill off any potential pathogens as the water makes contact with the mateiral.

While the lethality of silver for microbial lifeforms has long been known to modern science, this very property has thus far been hampered its use in water purification systems as it can also lead to a host of adverse effects for human heath.

Silver nano Porous Gel

Matthew Hu, a materials scientist from Singapore’s Nanyang Technological University and one of the leaders of the study, said the challenge for the team was producing a material which could avail itself of silver’s microbe-killing propensity, while at the same time preventing the metal itself from contaminating the water.

The team achieved this by first immersing a polymer gel in water at low temperatures, leading to the formation of tiny pockets of ice within the material. After thawing, the spongy material was left riddled with tiny pores.

Scientists then immersed the gel in a silver nitrate solution, followed by sodium borohydride, which pitted the surfaces of the gel’s pores with silver nanoparticles by binding them tightly to its polymeric material.

The final result of this process is a spongy material which absorbs water but does not taint it with silver when the liquid is subsequently squeezed out.

Tests have shown the gel is capable of reducing levels of E. coli and grass bacillus to a mere 0.1 per cent of their original levels within mere seconds of contact with water samples. The treatment also keeps concentrations of bioavailable silver in processed water well within the safety limits outlined by the World Health Organization.

Further testing by the team found that a mere four grams of the material, in the form of a cylinder 1.5 centimetres in diameter and nine centimetres in length, is capable of absorbing and purifying half a liter of water with a single squeeze.

The speed and safety of the process, as well as the lightness of the material, means the gel could be the ideal solution for the problem of obtaining potable drinking water in the wake of large-scale natural disasters.

Hu notes the material could be tossed into disaster zones from helicopters, after which point survivors can create safe, drinkable water by immersing the material in available supplies of water and then squeezing it.

Derek G. Gray, professor emeritus of material science at McGill University, said this ingenious technological solution is wholly unprecedented.

“The beauty is that the contact time between the water and the nanoparticles is controllable,” he said. “As far as I know, no one has come up with that before.”

The researchers now plan to run trials of the technology in Myanmar via a charitable project sponsored by Singapore’s Lien Foundation, while Nanyang graduate student and study author Siew-Leng Loo is also working on automated purification methods which make use of the gel.

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