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Solid Catalyst Quickly Neutralizes Chemical Weapons

ACS Meeting News: Zr-based MOF hydrolyzes phosphate ester linkages in highly toxic nerve agent

by Mitch Jacoby
March 26, 2015 | A version of this story appeared in Volume 93, Issue 13

A scheme showing the preparation of a MOF.
Credit: Nat. Mater.
The large pores in this MOF (below, left) enable organophosphate nerve agents to reach internal catalytic sites where they are neutralized via hydrolysis (reaction on right).Blue = Zr, red = O, gray = C, white = H, orange = P, green = F.

A metal-organic framework (MOF) compound catalyzes decomposition of the most toxic chemical warfare agents with record-setting efficiency, according to research presented at the American Chemical Society national meeting last week in Denver.

The findings may lead to new types of filtration media for gas masks and to improved procedures for destroying stockpiles of chemical weapons.

Chemical weapons based on organophosphate nerve agents such as soman, also known as GD, rank among the most toxic compounds known. The activated carbon and metal oxides widely used today in gas mask filters provide a measure of protection against these nerve agents. But scientists are looking to develop materials with greater capacity for trapping and chemically neutralizing nerve agents.

MOFs, which are porous crystalline materials composed of metal ions or clusters joined by organic linking groups, could meet those needs.

At a symposium sponsored by the Division of Physical Chemistry, Northwestern University’s Omar K. Farha reported on NU-1000, a new MOF built from Zr6 clusters linked by para-benzoate pyrene ligands. It features uncommonly wide channels measuring 31 Å in diameter (Nat. Mater. 2015, DOI: 10.1038/nmat4238). The large openings enable organophosphates to gain access to internal catalytic sites, where Lewis acidic Zr(IV) centers decompose the molecules via hydrolysis. In MOFs with smaller pores, such sites are largely inaccessible.

Farha and coworkers showed that in aqueous solution, NU-1000 acted 960 times as fast as a common Cu-based MOF. And in humid air, which closely simulates gas mask conditions, it neutralized GD 80 times as fast as the Cu-based MOF.

T. Grant Glover, a specialist in nanoporous materials at the University of South Alabama, Mobile, noted that NU-1000 is among the most active solid catalysts known to hydrolyze GD. The study also shows how MOFs, which are mainly used in gas separation and storage, are now being tailored for diverse applications.



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