What is happening in the Molecular Foundry

Artist's impression of water molecules. A research team led by Berkeley Lab has developed a new crystalline material that attacks and traps copper ions from wastewater with unprecedented precision and speed. (Image credit: Sashkin / Shutterstock)

W. We rely on water to quench our thirst and to irrigate abundant farmland. But what do you do when this once pristine water is polluted? Wastewater from abandoned copper mines?

One promising solution is based on materials that trap heavy metal atoms, such as copper ions, from wastewater through a process known as adsorption. However, commercially available copper ion trapping products still lack the chemical specificity and resilience to precisely separate heavy metals from water.

Now, a team of scientists led by the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a new crystalline material called ZIOS (zinc imidazole salicylaldoxime) that attacks and traps copper ions from wastewater with unprecedented precision and speed. In a recent article in the journal Nature Communication, scientists say ZIOS is offering the water industry and the research community the first blueprint for a water treatment technology that scavenges certain heavy metal ions with levels of control at the atomic level that far exceed the current state of the art.

“ZIOS has high adsorption capacity and the fastest copper adsorption kinetics of any material known to date, all rolled into one,” said Jeff Urban, senior author, Berkeley Labs Molecular Foundry Inorganic Nanostructures facility director.

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

For example, Urban has focused much of his research on the design of super-thin materials made from hard and soft matter for a variety of uses - low-cost water desalination to self-assembling 2D materials for renewable energy applications.

"And what we wanted to mimic here are the sophisticated functions that nature performs," ​​says the lead author, when proteins that make up a bacterial cell choose certain metals to regulate cell metabolism. Ngoc Bui, a former postdoctoral fellow in the Molecular Foundry at Berkeley Lab, who is now Assistant Professor of Chemistry, Biology, and Materials Engineering at the University of Oklahoma.

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

Such a specificity at the atomic level could also lead to cheaper water treatment techniques and support the recovery of precious metals. "Today's water treatment systems are 'mass separation technologies' - they pull out all solutes, regardless of their hazard or value," said co-author Peter Fiske, director of the National Alliance for Water Innovation (NAWI) and the Institute for Water Energy Resilience (WERRI) in the Berkeley Lab. “Highly selective, durable materials that can capture certain trace elements without becoming loaded with other solutes or falling apart over time are critical to reducing the cost and energy of water treatment. They can also enable us to break down wastewater into valuable metals or other trace elements. "

Catch heavy metals at the atomic level

Urban, Bui and co-authors report that ZIOS crystals are highly stable in water - up to 52 days. And in contrast to metal-organic frameworks, the new material is well suited for acidic solutions with the same pH range as for acidic mine waste water. In addition, ZIOS selectively traps copper ions 30-50 times faster than conventional copper adsorbents, according to the researchers.

From left: Schematic representation of a ZIOS network; and a SEM (scanning electron microscopy) image of a ZIOS copper sample on a silicon wafer. (Photo credit: Berkeley Lab)

These results surprised Bui. “At first I thought it was a mistake because the ZIOS crystals have a very small surface area and, according to conventional opinion, a material should have a high specific surface area, like other families of adsorbents such as organometallic frameworks. or porous aromatic scaffolds to have high adsorption capacity and extremely fast adsorption kinetics, ”she said. "So I asked myself,‘ Maybe something more dynamic is happening in the crystals. '"

To find out, she enlisted the help of co-lead author Hyungmook Kang to run molecular dynamics simulations at the Molecular Foundry. Kang is a PhD student in the Urban Lab of the Molecular Foundry of the Berkeley Lab and has a PhD Student in the mechanical engineering department at UC Berkeley.

Kang's models showed that when ZIOS was submerged in a watery environment, “worked like a sponge, but more structured,” Bui said. "Unlike a sponge that absorbs water and expands its structure in random directions, ZIOS expands in specific directions when it adsorbs water molecules."

X-ray experiments at Berkeley Lab's Advanced Light Source showed that the tiny pores or nanochannels of the material - only 2-3 angstroms, the size of a water molecule - expand even when immersed in water. This expansion is triggered by a "hydrogen bonding network" that is created when ZIOS interacts with the surrounding water molecules, Bui explained.

This expansion of the pores allows water molecules carrying copper ions to flow on a larger scale, causing a chemical reaction called a "coordination bond" between copper ions and ZIOS to take place.

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

In addition, the researchers said that when water is removed from the material, the crystal lattice structure contracts to its original size in less than 1 nanosecond (billionths of a second).

Co-author Robert Kostecki attributed the team's success to its 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 nanoscience, environmental science, and energy technology capabilities to transform a fundamental materials science discovery into a technology that has great potential for real impact." Kostecki is Director of Energy Storage and Distributed Resources at Berkeley Lab's Energy Technologies Division and R&D Materials and Manufacturing Lead in NAWI.

Next, the researchers plan to explore new design principles for the selective removal of other pollutants.

“Numerous families of materials have been developed in water science and the water industry for the decontamination of wastewater, but only a few are designed to remove heavy metals from acid mine drainage. We hope that 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 and Chaochao Dun, Tracy M. Mattox, Jeffrey R. Long, Peter Fiske, and Robert Kostecki.

Researchers from the Berkeley Lab; 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 energies, office for geothermal energy; and Berkeley Lab's Laboratory Directed Research and Development (LDRD) program.

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

The Molecular Foundry and Advanced Light Source are national user facilities in the Berkeley Lab.

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