The presence of toxic metals in water stemming from industrial sources makes treatment a tall order, with these polluted liquids capable of contaminating groundwater supplies for years or even decades thereafter. Scientists at Japan’s Nagoya University have come up with a new technology that may help stem the tide, using electrically charged nanocarbons to more effectively filter heavy metal ions from the mix.
Over the years we’ve seen a number of inventive approaches to removing trace amounts of toxic metals, such as arsenic, iron mercury, tin and lead, from industrial water sources. These have involved self-propelled microbots that wade through the samples to collect metal ions, filters made from quartz, and even onion and garlic waste.
Another possibility is the use of nanocarbons, tiny chunks of carbon-based material which have shown promise in water purification applications due to an ability to bind to heavy metal ions such as lead and mercury through molecular forces. Naturally, this attraction is weak, so the Nagoya University scientists are looking to supercharge things by tweaking the production process.
This involves doping the nanocarbons with molecules such as amino groups that create stronger chemical bonds with the metals. The team investigated this possibility by using phenol as their carbon material and mixing it with a compound called APTES as the amino group.
The ingredients were placed inside a glass chamber and exposed to a high-voltage electrical current over 20 minutes, which ultimately led to the formation of amino groups evenly across the surface of the nanocarbon, including on the surface of its tiny inner pores.
“Our single-step process facilitates the bonding of amino groups on both outer and inner surfaces of the porous nanocarbon,” says materials scientist Nagahiro Saito of Nagoya University. “This drastically increased their adsorption capacity compared to a nanocarbon on its own.”
The team then tested out the nanocarbon in experiments, comparing its performance to others produced through conventional means. The electrically charged nanocarbon had the highest adsorption capacity of any of them. In a separate experiment, the team put the nanocarbons through 10 adsorption cycles involving copper, zinc and cadmium metal ions, finding that though its performance declined each time, this reduction was small, indicating that it could offer a high degree of reusability.
“Our process could help reduce the costs of water purification and bring us closer to achieving universal and equitable access to safe and affordable drinking water for all by 2030,” says Saito.
A paper describing the research was published in the journal ACS Applied Nano Materials.