Magnetically separable reactive sorbent based on the CeO2/γ-Fe2O3 composite and its utilization for rapid degradation of the organophosphate pesticide parathion methyl and certain nerve agents

Abstract

A new kind of magnetically separable composite consisting of maghemite grains and cerium oxide nanocrystalline surface layer (CeO2/γ-Fe2O3) was successfully used as so called “reactive sorbent” to decompose certain dangerous organophosphate compounds, including the organophosphorus pesticide parathion methyl and the chemical warfare agents soman and VX. The phosphatase-mimetic behaviour of the sorbent was also demonstrated. A reversed-mode co-precipitation of Fe3+/Fe2+ salts with aqueous ammonia was used to prepare the magnetite core, with the subsequent precipitation of cerous carbonate on the surfaces of the magnetite grains (again in the reversed mode) and its conversion to cerium oxide by calcination in the presence of air. The magnetite was converted to maghemite during calcination. Scanning electron microscopy (SEM), high-resolution transmission microscopy (HRTEM) and electron diffraction (ED) confirmed the presence of the nanocrystalline layer of CeO2 on the sorbent surface. The CeO2/γ-Fe2O3 composite materials prepared at the optimum temperatures of 300–400°C exhibited the highest degradation efficiency and simultaneously retained good magnetic properties. Very high degradation rates (reaction half-lives of approximately ten minutes or less) were achieved at ambient temperature, with the degree of conversion approaching 100%. The facile separability of the sorbents using, for example, permanent magnets may enable their versatile use in various decontamination strategies.