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UChicago Pritzker School of Molecular Engineering (UChicago PME) Ph.D. student Leeann Sun is the first author of a recent paper opening up potential new applications for the pigment known as Prussian blue. Credit: Paul Dailing
The deep, murky pigment known as Prussian blue put the "blue" in traditional blueprints, colored Hokusai's "Great Wave off Kanagawa" and today is used for industrial purposes, from laundry to battery components to poison control. Now, research from the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) has found new uses for the important and inexpensive chemical and new understanding of the mechanisms that make Prussian blue analogs (PBAs) unique.
"Prussian blue is special," said UChicago PME Ph.D. student Leeann Sun, the first author of the new work recently published in Matter. "It can accommodate a lot of different ions because of its open structure. It's different from other materials that are really selective towards one element and intrinsically don't allow other ions in."
Using insights gleaned from synchrotron anomalous X-ray diffractions through NSF's ChemMatCARS beamline at the Advanced Photon Source (APS), Argonne National Laboratory, the UChicago PME team used the ion transport properties of the PBA copper hexacyanoferrate to achieve 99.9% lithium purity.
"We think this will be useful for purifying lithium solutions, pushing them to battery-grade," Sun said. "But this new understanding of the science behind Prussian blue will open up many opportunities, including separating monovalent and divalent ions commonly seen as industrial waste in water and other environmental streams."
UChicago PME Assoc. Prof. Chong Liu, the paper's corresponding author, said the results offer deeper understanding for identifying and harnessing chemical "handles" to enhance separation performance, with the ultimate goal of creating filters that can be tuned to let certain ions through while extracting others.
"We are providing a guideline of the correlations between the element you choose for the redox and the vacancy level you choose for the material, and—at the end—what kind of activity you will get for this material," Liu said.
Credit: Matter (2026). DOI: 10.1016/j.matt.2025.102575
The view inside the blue
Prussian blue analogs are famous for their color, but valuable for their structure. A deceptively simple family of iron-cyanide compounds, PBAs' unique 3D open framework is the ideal crystal structure for many types of filtration and purification. They're being explored as low-cost alternatives to lithium in batteries and often used medically if people accidentally eat heavy metals.
One major advantage for the blue? Cost.
"Because iron is one of the most abundant elements, this material is really easy to make," Liu said. "Any student can just come into the lab and quickly catch up on the precipitation method used to make Prussian blue."
To study PBAs, the team from Liu's lab turned to ChemMatCARS, a National Science Foundation supported center located at Sector 15, the Advanced Photon Source, Argonne National Laboratory that provides state-of-the-art synchrotron X-ray facilities and data analysis for molecular science and engineering researchers around the world.
The UChicago PME-led team used ChemMatCARS anomalous small- and wide-angle X-ray scattering (ASWAXS) instrument to perform synchrotron anomalous X-ray diffraction to study the material. This is a level of complexity beyond the small angle X-ray scattering (SAXS) commonly used to determine a material's structure.
"Any kind of scattering will give you structure, but we are doing more than that. We are sensitive to individual elements in that structure," said ChemMatCARS Beamline Scientist and Deputy Operations Manager Mrinal Bera, a co-author of the new paper. "Suppose you have a ball made of carbon, oxygen, nitrogen, and one critical mineral, lanthanide. If you do SAXS, you will just see it as a ball. But with our technique, we can tell you where that lanthanide is sitting within that ball."
Liu's lab used this to track where different ions sit within the PBA unit cell, giving unprecedented insight into which areas were still available to store and filter other ions.
"Monovalent ions like potassium, for example, will sit at a corner of the unit cell. So because of the vacancy, the center is usable. Divalent ions tend to sit in the center of the unit cell, leaving no vacancy, so the center is not usable," Liu said. "If you can store the ions at the corner, which is tighter and binds more strongly with the material, then the selectivity is better."
Publication details Leeann Sun et al, Selectivity mechanisms of ion intercalation in Prussian blue analogs, Matter (2026). DOI: 10.1016/j.matt.2025.102575 Journal information: Matter
— Source: Phys.org (https://phys.org/news/2026-02-prussian-blue-pigment-purification.html)
