Degradation of chemical warfare simulants over CeO2 and Gd-doped CeO2 aerogels: divergent results of DMMP and DFP

Abstract

Ceria (CeO₂) is a promising material for binding and degrading organophosphorus chemical warfare agents (CWAs). This oxide boasts reactive surface hydroxyls, offers a photo-excitable band gap state, and exhibits a propensity to form reactive oxygen species (ROS). Given the challenges of working with live CWAs, researchers generally evaluate CeO₂ and other reactive sorbents against a simulant molecule, but these simulants may differ in degradative pathways and fail to accurately predict performance of the sorbent against CWAs. Here, we report key divergence in the properties of Gd-doped CeO₂ (GCO) aerogels against two simulants, finding that Gd³⁺ substitution for Ce⁴⁺ impedes degradation of dimethyl methylphosphonate (DMMP) but improves degradation of diisopropyl fluorophosphonate (DFP). We attribute the difference to enhanced ROS stabilization on the GCO surface. Computational analysis of the two simulants as well as the CWA sarin (GB) reveals ROS improve the binding of fluorophosphorus molecules but not fluorine-free DMMP. Our findings identify GCO as a potentially effective material against CWAs and highlight the limits of DMMP as an arbiter for evaluating materials' efficacy.