Imagine a future in which a chemical attack on a Middle Eastern village in the dead of night has no effect on the people in its path. They are sleeping soundly in tents embedded with protective filtration material that prevents any harm. The village elders, who come out to investigate, have that same material in the headscarves they wear over their faces as they walk about with chemicals lingering in the air.
That day is coming closer. Two U.S. Army Edgewood Chemical Biological Center scientists, Greg Peterson and Jared DeCoste, are working with chemists at Northwestern University to make it a reality.
For the past eight years, Peterson and DeCoste have been steadily refining and improving a recently developed class of chemical compounds known as metal-organic frameworks, or MOFs. Chemists make them in a laboratory using organic struts and metallic nodes, much like an erector set, creating void spaces for chemical warfare agent, or CWA, or toxic industrial compound, or TIC, molecules to enter.
WHAT MAKES MOFs UNIQUE?
These modular building blocks are organic and inorganic molecular hybrids that take on the advantages of each. The inorganic characteristics give MOFs a very stable compartmentalized structure while the organic component gives them the dynamic quality of interacting with molecules that come into contact with them. Both the organic and inorganic components can be interchanged to create a variety of structures and properties designed to absorb or catalyze CWAs, TICs and other gases as desired. Thus, MOFs are truly nano-constructed designer materials.
As researchers continue to improve upon how precisely they assemble MOFs, the actions of these highly customized molecules will become dramatically more sophisticated. In theory, a sequence of MOF crystals could be structured so their pores serve as bays in which nano-manufactured proteins perform computing functions: counting, sorting and coding. This quickly leads to a future in which fibers, fabrics and even construction materials perform a wide range of intelligent functions.
For now, the Army scientists are concentrated on two key areas: protection and decontamination.
Peterson and DeCoste are working with a zirconium-based MOF, known as the UiO series, to take advantage of its broader filtration properties. They include removal of ammonia, cyanogen, chloride, blister agents and nerve agents. Their goal is to grow them on fibers that can transform a uniform, a tent or even a head scarf into personal protective equipment. This is a potential game-changer in the nation's efforts to establish stability in volatile Middle East countries that have suffered CWA attacks, such as Syria and Iraq.
Peterson and DeCoste are also working on a new MOF, known as NU-1000, created by their research partners at Northwestern. NU-100 doesn't just trap the CWA molecules but breaks their bonds on contact. With the addition of water to flush the MOFs out, these MOFs do not get saturated and can keep on working. Because of that, this new MOF neutralizes agent eighty times faster than other MOFs created thus far.
In addition, NU-1000 remains stable for years at both extremely high and extremely low temperatures, and is able to take the water needed to conduct CWA neutralization out of the atmosphere. These qualities make it much more effective when used in protective mask filters, building filters, and as a decontamination material.
As Peterson and DeCoste, and their research collaborators at Northwestern and several other research universities, gained more knowledge of MOFs through their protection research, applications to decontamination starting becoming apparent. They saw that the MOFs they were working with actually decompose entire classes of chemical warfare agent or toxic industrial compounds on contact and in bulk, especially in the presence of moisture. But to fully exploit this characteristic, they have to find the MOF sweet spot.
"We are working with our university partners to design a MOF with both the best pore structure for agents to enter, and the most reaction sites where the decomposition occurs. This is hard because while big pores take in large molecules, they also place the reactive sites farther apart. We're working on getting the right balance," Peterson said.
Ultimately, Peterson and DeCoste hope to develop a decontamination powder that can be used to neutralize CWAs found in the field, and even a MOF aerosol that can be sprayed on a CWA-exposed surface such as an armored personnel carrier.
As Army scientists and their university colleagues create more sophisticated MOFs, their application may lead to a more innovative and effective chemical, biological defense.
Source: US Army
Date: Jul 14, 2015