AD: What are zeolites?
DV: They're aluminum silicate structures that are shot through with pores and cavities of molecular dimension, usually less than 1 nanometer. Think of a sponge with pores only big enough to allow certain molecules in. Whether the zeolite allows the molecule in depends on the size and charge of the ion as well as the pore space in the zeolite. Zeolites are choosy. Whichever cation, or positively charged atom, has the stronger bond or attraction to the slightly negatively charged framework of the zeolite will bump off other cations. One zeolite might be better at soaking up hydrogen, while another might be best designed to suck up ammonia. Most zeolites have sorptive properties that allow them to absorb molecules into their structure and permit molecules to adhere to outside surfaces.
AD: How might zeolites help us deal with bioterrorism?
DV: Zeolites could help address the problem of bioterrorism as it affects the food supply. For instance, after the Chernobyl nuclear disaster in 1986, zeolites were used to prevent slow-developing cancers associated with nuclear fallout. Zeolites were ground up and added to flour to prevent radioactive elements from being absorbed by the bones. In the gut, zeolite scavenges these radioactive elements. Later, the radioactive cesium or strontium is trapped in the zeolite and is excreted. Zeolites could also be used to sense highly toxic gases, such as hydrogen sulfide. Many researchers are looking at zeolite-based coatings or membranes for gas detection.
AD: What's their future market potential?
DV: Zeolites could be used to make more environmentally friendly products. Currently, we have a lot polymers or plastics in carpets and paint. Some people are supersensitive to certain organic chemicals, such as formaldehyde, a byproduct of the plastics used to build houses. By using zeolites to soak this up indefinitely, we could reduce the levels of such contaminants in the air.
AD: How could they make gas storage safer?
DV: Environmentalists tout hydrogen as the perfect clean fuel; its only byproduct upon combustion is water. But it's also highly volatile in air. If you accumulate enough of it, your turning on the light as you go into the garage would be enough to set off an explosion. One big problem that has yet to be solved is how to store such a gas safely. Now, it's stored in high-pressure containers. But in a collision, such a high-pressure tank is likely to explode. A tank filled with zeolite could store the same amount of hydrogen at a fraction of the pressure. In a crash, the hydrogen would seep out of the tank more slowly, so you wouldn't have a sudden burst of flame. You could also have a smaller tank, which would make your car more efficient by cutting its weight.
Potential applications also include using zeolites in cosmetics. You can trap and encapsulate molecules that would be slowly released to the skin. Similar applications in pharmaceuticals are possible but haven't been researched much.
AD: Where will we see zeolites used more in the future?
DV: Many areas are already pumping purified wastewater back into the ground to conserve water. Part of the treatment involves running the water through a bed of zeolite to remove the ammonia that comes from waste products and fertilizer runoff, making what was once wastewater drinkable. This is a market that's likely to grow, given the looming water shortage in the Western states.
DAVID E. VAUGHAN
The problem of secure storage has confounded us since the days of Pandora. Now, with the escalated threat of terrorism, the issue has become more pressing. Whether it's radiation unleashed or tainted food, how can we prevent harmful substances from being released into the environment?
One answer is using zeolite, a type of rock that acts like a sponge. Zeolites can soak up undesirable molecules and store them indefinitely. Unlike most sponges, they release their contents only when heated to temperatures of hundreds of degrees centigrade. These traits make zeolites suitable for capturing and storing contaminants. They can selectively attract and soak up liquids and gases at the molecular level, making them useful in products from cat litter to water treatment.
First synthesized in the 1800s by German scientists who wanted to remove excess salts from the soil, by the 1950s zeolites were used to purify industrial gases. Just as suburban development was driving up the demand for gas in the 1960s, Exxon and Mobil used zeolites in petrochemical processes to convert crude oil to fuel while increasing purity and yield.
â€œZeolites will continue to be the premier material for molecular engineering,â€? says David Vaughan, senior scientist at Penn State, who holds 85 patents relating to zeolite synthesis and their use in petrochemical processes. Vaughan spoke with American Demographics' Sandra Yin about future applications of zeolites.