Sometimes, combining two things that don’t normally go together makes for something better than its individual parts.
Think of oil and vinegar. Though normally the two don’t mix, extra virgin olive oil whisked up with a splash of balsamic becomes a delicious salad dressing.
In the realm of conventional materials science, metals and organic molecules usually don’t mix, or rarely mix at the bulk level as composites. But when combined in the molecular and atomic level, metals and organics can create new solid state compounds with a vast array of properties that could be useful in applications ranging from advanced electronics to medicine.
Those combinations are called metal-organic frameworks, and Dawei Feng, a new assistant professor in the University of Wisconsin-Madison Department of Materials Science and Engineering, aims to harness their properties to push the limits of conventional materials.
“We don’t limit ourselves to specific applications,” says Feng. “We are seeking opportunities. Wherever we see opportunities where metal-organic frameworks can do better than conventional materials, we go deeper.”
One reason metal-organic frameworks are such versatile materials is that they usually consist, at a molecular level, of a regularly repeating network structure with wide-open channels. Those pores can trap specific compounds, act as a sieve or serve as miniature chemical reaction chambers.
Most of the applications for metal organic frameworks take advantage of their porous structures, and their physical properties as bulk solid state materials largely remain unexplored. Feng aims to bring some of those promising uses for the materials to light with his research at UW-Madison.
Feng learned to synthesize metal-organic frameworks during his PhD at Texas A&M University. There he helped develop materials that could scavenge antibiotics and explosives from water, absorbents for natural gas storage, as well as frameworks that could speed up some of the chemical reactions that occur in living cells.
During Feng’s postdoctoral work at Stanford University, he made a conductive metal-organic framework with record high performance as an electrode material in a electrochemical energy storage device called a pseudocapacitor. It’s an advance that could lead to ultrafast-charging and discharging energy storage devices.
Metal-organic frameworks, as their name suggests, consist of metal atoms like copper or nickel or zirconium networked with organic molecules, which are the carbon-containing compounds that make up all life on earth. The metal components lend the materials electronic and magnetic properties, whereas the organic molecules provide structure, stability and customizability while also bridging the gaps between metallic atoms to facilitate interactions.
Because the periodic table contains 91 metal elements, and there are untold thousands of different organic compounds, a dizzying array of possible combinations opens up.
By strategically selecting metals and organics, Feng tunes the frameworks he creates for a variety of uses. He likens the synthesis of metal organic frameworks to a construction project.
“It’s kind of like building a house for molecules and atoms,” says Feng. “You can put different pieces together and imagine what furniture you want to have in the house, and you put things together step by step, and eventually decorate the house with different functionalities as desired.”
At UW-Madison, Feng plans to delve deeper into the physical properties of metal-organic frameworks, including ion conductivity and electronic properties. In addition to furthering his work on energy storage, Feng sees promise in using the materials to find new semiconductors for advanced electronic devices.
“In theory, if we can choose the right metal and the right organic molecules we could build up to thousands of completely new semiconductors or ion conductors,” says Feng. “The possibilities are huge, but there needs to be a big synthetic effort.”
Feng’s focus is not limited to developing new ion conductors and electronic materials—he’s committed to synthesizing new frameworks and following the most promising properties to their logical applications.
He also has begun discussing collaborations with his colleagues, including Chang-Beom Eom, the Raymond R. Holton Chair Professor and Theodore H. Geballe Professor in materials science and engineering and a world expert in materials synthesis as well as Professor Padma Gopalan, a leading researcher in polymer synthesis.
The collegial environment at UW-Madison was a major factor in Feng’s decision to join the MS&E faculty.
“The people surrounding you are the most important thing in your environment,” he says.
Author: Sam Million-Weaver