Room temperature decomposition of dimethyl methylphosphonate on cuprous oxide yields atomic phosphorus

Abstract

Organophosphorus compounds have a wide range of reactivity depending on the coordination and oxidation state of the P atom. Due to their toxicity, certain organophosphonates are used as pesticides, herbicides, and, notoriously, as chemical nerve agents. The organophosphonate decomposition mechanism depends strongly on the substrate material, which motivates careful analysis of a range of potential materials for decontamination and sensing applications. Here, we present a study of the decomposition of dimethyl methylphosphonate (DMMP), a simulant molecule for the nerve agent sarin, on polycrystalline cuprous oxide surfaces (Cu2O). We use ambient pressure X-ray photoelectron spectroscopy (APXPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to monitor the pressure-dependent surface chemistry during exposure to DMMP vapor. At room temperature, we observe extensive degradation of DMMP, which includes the formation of reduced P products on the sample surface. We identify five unique P-containing species in the P 2p APXPS spectra, including atomic P and a surface-bound phosphinate [OPH(OCH3)OCu]. We propose a DMMP decomposition pathway whereby accumulation of this phosphinate species leads to an autocatalytic reaction on the Cu2O surface which yields reduced P species. After DMMP exposure, heating the Cu2O sample to 265 °C leads to complete removal of all carbonaceous species and accumulation of a phosphate layer with stoichiometry similar to P2O5. These results introduce a new mechanism of room-temperature DMMP decomposition on metal oxides, which could be leveraged for the design of tailored metal oxide materials for catalyzing organophosphonate decomposition.