Anthony King
A nanoparticle-coated sponge could offer a useful tool for removing pollutants from water.
A reusable sponge thinly coated in nanoparticles can trap heavy metals in water, scientists report. As a demonstration, the lab of Vinayak Dravid at Northwestern University, US, successfully filtered lead-contaminated water at concentrations around 1ppm, achieving levels below detection.
The lead was picked up by manganese-doped goethite nanoparticles coated in a cellulose membrane. The metal ions were then removed from the sponge by rinsing with mildly acidified water, freeing the sponge for reuse. The capability to recover metals could be useful for cleaning water, but also for sourcing valuable metals such as cobalt or copper from tailings ponds or from wastewater in battery production facilities.
The coating used for the lead demonstration was made from cellulose and is an ideal material when metals are present in low concentrations, such as parts per million, and there is a high flow of water through the membrane. Where there is a lot of organic matter or concentrated amounts of metals, such as in tailings ponds, a hydrophobic polyurethane sponge would be used instead, explains Dravid.
This is not the first time the team has applied this technology. In 2020, they described a sponge that could selectively soak up oil with a magnetic nanocomposite coating.
‘We developed this technology to remove pollutants, starting with oil,’ says Dravid. ‘This is a sort of Swiss Army knife approach to pollution we’ve been working on for the last few years in order to sequester pollutants based on changing the coating but keeping the sponge the same.’
The team chose lead in this demonstration because heavy metal consumption – such as lead, arsenic and chromium – is tied to higher mortality and a wide range of detrimental health outcomes. Dravid estimates that their technology for removing metals could be ready for commercialisation within three-to-five years.
‘They are reporting quite an impressive percentage removal of metals, and they get good recyclability [of the filter system],’ says Ashleigh Fletcher, Professor of chemical and process engineering at the University of Strathclyde, UK. The performance of their sponge in removing copper was almost as good, she says.
She adds that the nanoparticles grabbing the metals was not unexpected; rather it is the hosting and controlling of the morphology of the material on the cellulose membrane that is novel. ‘You can dunk this membrane in water and take it back out or have the water flow through the membrane to remove the metals,’ she adds.
Fletcher says the next step is to test the performance of the filter with water that contains a mixture of competing metals, the sort of competitive adsorption that often exists in real-life situations.
Dravid has co-founded a startup company, MFNS-Tech, to commercialise the sponge-based approach for environmental remediation, with a licence from Northwestern.
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