Like the hunter who finally catches the fox, Kenneth Balkus, Jr., PhD, professor of chemistry, must be pleased whenever he develops a better chemical trap.
Balkus has spent much of his 17 years of research at The University of Texas at Dallas [UT Dallas] working with zeolite materials — porous crystalline metal oxides that act as ion-exchangers and are used in water softening and as absorbents and catalysts.
"We started using these materials as hosts for catalysts. Putting metal complexes inside and trying to make what we call ‘ship in the bottle’ catalysts. And part of the motivation for a lot of that work is to mimic enzymes," Balkus said in his office in Berkner Hall.
Balkus grew strategies for synthesizing zeolites around catalysts. That’s how his lab made many of the materials, including UTD-1, the largest pore zeolite known.
"We’ve also made other classes of material known as mesoporous materials molecular sieves, including DAM-1, which stands for Dallas Amorphous Material No.1, in addition to much larger pore materials. In this case we can actually immobilize enzymes. We were the first ones to do that," Balkus said.
Beyond gatekeeping capabilities
He's talking about sieves, those mesh devices through which finer particles of a mixture may be passed to separate them from coarser ones. These, however, are on a molecular level. And his ship-in-a-bottle analogy is dead-on: Imagine the patience and steadiness required to place in order each ship piece slowly stacked atop one another inside the bottle until its completed. It's the same thing here. Within the pores of many of these finely structured sieves he is placing organic materials to allow them to work more like enzymes.
"Molecular sieves imply that you separate things, based on size and shape, but with zeolites you can separate small molecules. For example, we can synthesize zeolites with pores smaller than 1nm that will exclude molecules larger than 1 nm. We can also prepare molecular sieves with pores in the range of 2-50 nm which will acommodate much larger molecules.
"You can separate ethanol and water, for example, or alcohol or inorganics and water. And that’s a potential application of these types of materials.
"We’re interested in making membranes out of these materials. And we use a technique known as pulse-laser deposition to make our membranes. We have an excimer laser upstairs, and we can — actually, we have a pretty cool video of the laser."
Balkus showed the video, explaining the ablation process (see image below).
“So this is the laser beam coming in here. And it’s striking a target up here and depositing film. Now the laser beam is actually ultraviolet light, so you can’t see it with your eyes. The light that you are seeing here is this plume of particles being generated as the laser beam strikes the target and then deposits onto a substrate.
"This plume of material gets deposited onto our substrate, and that’s how we make our membranes. We can actually coat just about anything using this technique, so not only do we make flat membranes for things like gas separations, but imagine these materials also separating things by size and shape where you can use them in sensors. You can discriminate molecules as they absorb into your sensor. So we have a program in sensors based on these tools.
"We can coat three-dimensional objects to make core shell structures with applications in drug delivery, for example. We are looking at applications in nanocatalysis. We can take advantage of the porosity of these particles to template the growth of nanorods and nanofibers of semiconductors or our molecular sieves. These have applications in solar cells as well as catalysis," Balkus said.
Balkus said he's had the most collaborations with Ferraris, because they complement each other.
"He’s the organic materials person and I’m the inorganic materials person, and so we're together anytime there’s a project involved with a hybrid or combination of these materials. Plus he’s a Yankee and I’m a Yankee, so we get along well," he said with a cheerful smile.
They actually have several collaborative projects, including putting these materials into polymer membranes. In another project with Drs. Ferraris and Inga Musselman they have assembled a state-of-the-art membrane permeameter.
"We have a fuel cell project, again working with membranes and using some of these materials for their conductivity to use in a fuel cell," Balkus said.
Twenty years ago he'd have been considered an inorganic chemist because of the types of materials he works with. Today Balkus is a materials chemist.
"Many things that we work on qualify as nanotechnology, but probably only recently have people started to use that terminology to describe these types of materials.
"We do a little bit of biology without a license, but I wouldn’t say we are biochemists. Even though we play with enzymes and cells, we are really materials chemists," he said. "I have a student who is using these fibers as scaffolds for growing cells. It’s a joint project we are doing with Rockford Draper, PhD in the biology department.
"We use a technique called electrospinning, where we make our materials a sort of precursor gel. All zeolite materials, while they may end up as a crystalline powder or ceramic type of material, can be manipulated in different ways. So just like with lasers we can make films or coatings, by electrospinning we can make fibers.
"We can actually make free standing papers, coatings, using this technique. So we are doing lots of different things with these fibers. You can imagine smart textiles and smart papers," Balkus said.
In the classroom
For the past 17 years, Balkus mostly has taught inorganic chemsitry and an upper division advanced synthesis course. Students actually get into a laboratory, learn how to do synthesis and keep a laboratory notebook, he said.
"I think it’s a fun lab because you teach them hands-on how they’ll actually do various techniques and measurements and the proper way to document all that," Balkus said.
There is a program to try to synthesize new metal organic frameworks.
In collaboration with the John Sibert, PhD, lab, Balkus said he hopes to use their expertise in organic chemistry to help "design linkers, trying to make new frameworks."
"My lab and the Sibert lab operate on different scales, I think. He’s making ligands that actually will sequester small ions and maybe a very small molecule. So it’s a completely different scale.
"We are looking at things that would separate on a much larger scale. Now, some of the molecules that he’s making that we’re using were self-assembling into three-dimensional architectures, where they are more interested in the free molecules. Although you do some immobilization onto supports, it’s hard to largely focus in on an individual molecule," Balkus said.
Greg Hundt, a doctoral candidate working in the Sibert lab who is profiled in the graduates section, was technically in the Balkus lab collaborating on a project from September to December 2004. While Balkus makes zeolite material, which are metal oxides, he also makes more immediate materials that are hybrids. They have organic functionality built into their frameworks and are called metal organic frameworks. And while they may not have the same stability of a pure metal oxide, they have some of same type of porosity and surface areas, which is a mark of molecular sieves.
"Greg's area of expertise is making bridging ligands and the things that allow us to assemble these framework type materials. Let me see if I have an example," he said.
Balkus searches his computer for the image shown above.
"So these would be pure metal oxides here like our DAM-1 material. And then these would be considered hybrid frameworks because you can see the pores have all these organic molecules that line those pores. And then these are those metal organic frameworks that I was just taking about where you’ve got an organic linker here and some metal ions here and then this gets connected into a three-dimensional framework so it becomes really porous.
"So what Greg was helping us with is designing these types of ligands to self-assemble and make these open, porous structures.
"This particular material here is actually a very good absorbent for methane and hydrogen. And so one of the things we are doing is putting these things into membranes to selectively transport hydrogen and methane," Balkus said.
Balkus said that crystal-ball gazing — looking into the future — is a waste of time in his line of work.
"We are very opportunistic. We follow ideas as they happen. So it’s difficult to predict what we’ll be doing five years down the road.
"Plus, I like to do things that nobody has ever done before rather than saying, 'Well, if somebody has done this, maybe we can do it a little bit better.' Derivative type work gets boring very quickly.
"I guess maybe I prefer doing more high risk stuff. I like to do things that are more original. Things that, in a research article, someone might say, 'Balkus did this first back in 1996.' When you see stuff like that, that’s what you show the students and say, 'See, that’s what it’s all about.'”
- Updated: September 2, 2010