The present invention relates to compositions and methods for sorbing (e.g., adsorption and chemisorption) and destroying organophosphate chemical agents. In certain embodiments, the invention contemplates the use of finely divided, modified nanoscale metal oxide particles. In one embodiment, a suspension of magnetite (Fe.sub.3O.sub.4) nanoparticles modified with 2-pralidoxime or its polymeric analog, poly(4-vinylpyridine-N-phenacyloxime-co-acrylic acid), catalyzes the hydrolysis of organophosphate compounds at a neutral pH. The oxime-modified magnetite particles serve as a nano-sized particulate carrier with a powerful .alpha.-nucleophile, an oximate group, immobilized on its surface. The oxime-modified magnetite nanoparticles are colloidally stable at neutral pH and they are readily recovered from the aqueous milieu by high-gradient magnetic separation methods.