Scientists design a new framework for clean water

WWe rely on water to quench our thirst and to irrigate abundant agricultural land. But what do you do when that once pristine water is polluted by the wastewater of abandoned copper mines?

A promising solution is based on materials that capture heavy metal atoms, such as copper ions, from wastewater through a separation process called adsorption. However, commercially available copper ion capture products still lack the chemical specificity and carrying capacity to accurately separate heavy metals from water.

Now, a team of scientists led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has designed a new crystalline material – called ZIOS (zinc imidazole salicylaldoxime) – that targets and traps copper ions from wastewater with unprecedented precision and speed. In an article recently published in the journal Nature Communications, scientists say ZIOS offers the water industry and the research community the first blueprint for a water remediation technology that removes specific heavy metal ions with a control measure at the atomic level, which far exceeds the current state of the art.

“ZIOS has high adsorption capacity and the fastest adsorption kinetics of copper of any material known to date, all in one,” said senior author Jeff Urban, who directs the Inorganic Nanostructures Facility at Berkeley Lab’s Molecular Foundry. .

This research embodies the distinctive work of the Molecular Foundry: the design, synthesis and characterization of nanoscale (billionths of a meter) optimized materials for sophisticated new applications in medicine, catalysis, renewable energy and more.

For example, Urban has focused much of its research on designing super thin materials from hard and soft matter for a variety of applications, from cost-effective water desalination to self-assembling 2D materials for renewable energy applications.

“And what we have tried to mimic here are the sophisticated functions performed by nature,” such as when the proteins that make up a bacterial cell select certain metals to regulate cell metabolism, said lead author Ngoc Bui, a former researcher. Molecular Foundry postdoc from Berkeley Lab who is now an assistant professor of chemical, biological and materials engineering at the University of Oklahoma.

“ZIOS helps us select and remove only copper, a contaminant in water that has been linked to disease and organ failure, without removing desirable ions, such as essential nutrients or minerals,” he added.

Such atomic specificity could also lead to cheaper water treatment techniques and favor the recovery of precious metals. “Today’s water treatment systems are ‘bulk separation technologies’ – they extract all solutes, regardless of their risk or value,” said co-author Peter Fiske, director of the National Alliance for Water Innovation (NAWI) and Water- Energy Resilience Institute (WERRI) at Berkeley Lab. “Highly selective and durable materials that can capture specific trace constituents without being charged with other solutes or falling apart over time, will be critically important in reducing the cost and energy of treating the ‘water. They may also allow us to “extract” precious metals or other trace constituents from wastewater. “

Heavy metal scavenging at the atomic level

Urban, Bui and co-authors report that ZIOS crystals are highly stable in water – up to 52 days. And unlike metal-organic structures, the new material performs well in acid solutions with the same pH range as wastewater from acid mines. Additionally, ZIOS selectively captures copper ions 30-50 times faster than cutting-edge copper adsorbents, the researchers say.

From left: schematic diagram of a ZIOS network; and a SEM (scanning electron microscopy) image of a ZIOS copper sample on a silicon wafer. (Credit: Berkeley Lab)

These results took Bui by surprise. “At first I thought it was a mistake, because ZIOS crystals have a very low surface area and, according to conventional wisdom, a material should have a high specific surface, like other families of adsorbents, such as metal-organic structures, or porous aromatic structures, to have a high adsorption capacity and extremely fast adsorption kinetics, “he said. “So I asked myself, ‘Maybe something more dynamic is happening inside the crystals.'”

To find out, he enlisted the help of co-lead author Hyungmook Kang to run molecular dynamics simulations at the Molecular Foundry. Kang is a research graduate student at the Urban Lab at the Berkeley Lab Molecular Foundry and a Ph.D. student in the mechanical engineering department at UC Berkeley.

Kang’s models revealed that ZIOS, when immersed in a watery environment, “works like a sponge, but in a more structured way,” Bui said. “Unlike a sponge that absorbs water and expands its structure in random directions, ZIOS expands in specific directions while adsorbing water molecules.”

X-ray experiments at the Berkeley Lab’s advanced light source revealed that the material’s tiny pores or nanochannels – just 2-3 angstroms, the size of a water molecule – also expand when submerged in water. This expansion is triggered by a “hydrogen bonding network,” which is created when ZIOS interacts with surrounding water molecules, Bui explained.

This pore expansion allows water molecules carrying copper ions to flow on a larger scale, during which a chemical reaction called “coordination bond” takes place between copper ions and ZIOS.

Further X-ray experiments showed that ZIOS is highly selective for copper ions at a pH below 3 – a significant finding, as the acid mine drainage pH is typically a pH of 4 or below.

Furthermore, the researchers said that when water is removed from the material, its crystalline lattice structure contracts to its original size within less than 1 nanosecond (billionth of a second).

Co-author Robert Kostecki attributed the team’s success to their interdisciplinary approach. “The selective extraction of elements and minerals from natural and produced waters is a complex scientific and technological problem,” he said. “For this study, we leveraged Berkeley Lab’s unique capabilities in nanoscience, environmental science and energy technologies to transform a basic materials science discovery into a technology that has great potential for real-world impact.” Kostecki is the director of the Energy Storage and Distributed Resources division in the Energy Technologies area of ​​Berkeley Lab and the Materials Research and Development and Manufacturing topic area at NAWI.

The researchers now intend to explore new design principles for the selective removal of other pollutants.

“In water science and the water industry, many families of materials have been designed for wastewater decontamination, but few are designed for the removal of heavy metals from acid mine drainage. We hope ZIOS can help change that, “said Urban.

Co-authors with Bui and Urban include Hyungmook Kang, Simon J. Teat, Gregory M. Su, Chih-Wen Pao, Yi-Sheng Liu, Edmond W. Zaia, Jinghua Guo, Jeng-Lung Chen, Katie R. Meihaus, Chaochao Dun, Tracy M. Mattox, Jeffrey R. Long, Peter Fiske, and Robert Kostecki.

Berkeley Lab researchers; UC Berkeley; the University of Oklahoma; and the National Synchrotron Radiation Research Center, Taiwan, participated in the study.

This work was supported by the DOE Office of Science; Energy Efficiency and Renewable Energy, Geothermal Office; and Berkeley Lab’s Laboratory Directed Research and Development (LDRD) program.

NAWI was recently selected to lead a Department of Energy water desalination hub to provide safe and affordable water. The five-year investment of $ 100 million represents the largest federal investment in water research in half a century.

The Molecular Foundry and Advanced Light Source are national user facilities co-located at Berkeley Lab.