Synthesis routes of CeO2 nanoparticles dedicated to organophosphorus degradation: a benchmark

Abstract

Exposure to organophosphorus compounds, in military conflicts or terrorist acts, requires an emergency procedure including the availability of efficient decontamination systems. Systems based on nanosized cerium(IV) oxide (CeO₂) are highly promising candidates. CeO₂ is a heterogeneous catalyst for the degradation of the organophosphorus compounds such as VX agent or sarin. While the synthesis method influences the physicochemical characteristics of the nanoparticle surface and thus their degradation activity, we have compared the degradation activity of nanosized CeO₂ powders commercially available, or developed using different synthesis processes, namely hydrothermal process, photochemistry and laser ablation in liquids. The degradation activity was evaluated in vitro by measuring the degradation kinetics of paraoxon organophosphate. A quenching of the degradation activity is observed on the as-produced particles with a surface pollution, especially when organic molecules with carboxylate ion R–COO⁻ are involved in the synthesis process. In contrast, laser-generated nanoparticles in ultra-pure water show the best activity, while the sample presents the lowest specific surface area. After annealing, almost all samples present a clean surface and the degradation activity is mainly driven by the specific surface area. We propose a figure of merit including the particle activity for the degradation of paraoxon, the production costs and the production time. Indeed, the two last parameters are essential to assess the relevance of each method in view of marketing.