Engineers from Northwestern University have created a new type of sponge that can extract metals such as lead and cobalt from polluted water, resulting in clean and safe drinking water.
The researchers conducted a proof-of-concept experiment to test the effectiveness of their new sponge in tap water contaminated with more than 1 part per million of lead. After using the sponge once, the lead level in the water reduced below detectable levels.
The new sponge developed by Northwestern University engineers can remove metals from contaminated water, including toxic heavy metals such as lead and critical metals such as cobalt, leaving water that is safe and potable. In the experiment, the sponges were tested in highly contaminated tap water, and after one use, the sponges filtered out lead to below detectable levels. Additionally, the researchers were able to recover the metal and reuse the sponge for multiple cycles. The new sponge has potential for use in home water filters or large-scale environmental improvement efforts.
Yesterday (May 10, 2023), a study was published in the journal ACS ES&T Water. This study discusses new methods for removing toxic heavy metals such as lead, and also suggests ways to improve the design of these methods for removing other toxins such as cadmium, arsenic, cobalt and chromium.
Vinayak Dravid, senior author of the study, said that the presence of heavy metals in water is a significant public health problem for the whole world. He said that it was a big problem that required an easy-to-use, effective and cost-effective solution. Dravid also states that their sponge can remove pollution from water and can be used over and over again.
Dravid is the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering and director of global initiatives at the International Institute for Nanotechnology.
Settlement of Spills
Previous Dravidian work involved developing highly porous sponges for environmental remedial purposes. In May 2020, he and his team created a sponge that can clean up oil spills. Sponges, coated with nanoparticles, are more efficient, economical, environmentally friendly, and reusable than current oil spill cleanup methods. MFNS Tech, a Northwestern spin-off, is now commercializing nanoparticle-coated sponges.
But Dravid knew that wasn’t enough.
Dravid explained that during an oil spill, not only oil but also toxic heavy metals such as mercury, cadmium, sulfur and lead may be present in the water. While the oil can be removed, toxic heavy metals may still be left behind.
Rinse and Repeat
The Dravid team used sponges coated with ultra-thin layers of nanoparticles to tackle toxic heavy metals, such as mercury, cadmium, sulfur and lead, found in oil spills. They experimented with different types of nanoparticles and found that a layer of manganese-doped goethite worked best. Goethite nanoparticles doped with manganese are easy to produce, affordable, and safe for humans. They also possess the necessary properties for the selective removal of heavy metals.
According to Benjamin Shindel, Ph.D. student in the Dravid lab and first author of the paper, the materials used needed to have a large surface area to allow more space for lead ions to attach to them. Manganese-doped goethite nanoparticles fulfill this requirement due to their high surface area and many reactive surface sites for adsorption. Moreover, they are stable and can be reused multiple times.
To make the sponge, the researchers produced a mixture of manganese-doped goethite nanoparticles and other types of nanoparticles, which they then used to coat the cellulose sponge. The coated sponge is then rinsed with water to remove excess particles, leaving a very thin layer only tens of nanometers thick.
The researchers coated a commercially available cellulose sponge with manganese-doped goethite nanoparticles, which were then rinsed with water to remove loose particles. These nanoparticle-coated sponges were then soaked in contaminated water and were able to trap lead ions effectively. In filtration experiments, the sponge was able to lower the amount of lead to about 2 parts per billion, which is below the FDA’s requirements for safe drinking water (under 5 parts per billion).
Benjamin Shindel, first author of the paper, expressed satisfaction with the results of the nanoparticle-coated sponge. However, he notes that sponge performance can vary depending on the situation. For example, a large sponge in a small amount of water will do better than a small sponge in a large lake.
Recovery Past Mining
After using a sponge to filter lead from the contaminated water, the researchers rinsed it in slightly acidic water. The acid solution makes the sponge release trapped lead ions and can be reused. Although the performance of the sponge decreased slightly after the first use, it was still able to recover more than 90% of lead ions in subsequent use cycles.
The ability to collect and recover these heavy metals is invaluable for removing rare and critical metals, such as cobalt, from water sources. A common ingredient in lithium-ion batteries, cobalt is extremely expensive to mine and comes with a laundry list of environmental and human costs.
If researchers can develop sponges that selectively remove rare metals, including cobalt, from water, then those metals could be recycled into products such as batteries.
Dravid emphasizes the importance of metal recovery in renewable energy technologies such as batteries and fuel cells. He said that without recovery of the metal, there would not be enough cobalt in the world to increase the number of batteries. Metals sitting in water became toxic and toxic, so it was necessary to find ways to recover metals from aqueous solutions. Dravids suggested that creating something of value out of recovered metal could be a fruitful solution.
In the study, Dravid and his team set new guidelines to assist others in creating tools to target specific metals such as cobalt. They identified low-cost, non-toxic nanoparticles that have a high surface area and can attach to metal ions. They evaluated how coatings of manganese, iron, aluminum and zinc oxide performed in lead adsorption and established a relationship between the structure of these nanoparticles and their adsorptive characteristics.
Called Nanomaterial Sponge Coatings for Heavy Metals (or “Nano-SCHeMe”), the environmental remediation platform could help other researchers distinguish which nanomaterials are best suited for a particular application.
Caroline Harms, a co-author of the paper and an undergraduate student in the Dravid lab, mentions that there is a lack of standardization in the field of comparison of different coatings and adsorbents. The team analyzed different types of nanoparticles and established a usable comparative scale for all of them, which could have significant implications in moving the field forward.
The team led by Dravid envisioned their sponge could serve a variety of applications such as commercial water filters, environmental improvement efforts, or as an added step in water treatment and reclamation facilities.
“This work may be related to water quality issues both locally and globally,” said Shindal. “We want to see this in the world, where it can make a real impact.”
Learning, “Nano-SCHeME: Nanomaterial Sponge Coatings for Heavy Metals, an environmental remediation platform,” supported by the National Science Foundation and the US Department of Energy.