Sarin Adsorption and Decomposition on Semiwet Surfaces: Density Functional Theory Insight

In this study, we investigated the adsorption and decomposition mechanisms of the organophosphorus nerve agent Sarin on reduced graphene oxide (rGO) and transition metal oxide (TMO) systems (TMO = CoO, NiO, CuO, ZnO) using density functional theory (DFT). Three key decomposition pathways of Sarin, P-F bond cleavage, P-O bond cleavage in P-OC₃H₇, and isopropyl elimination, were investigated in detail. For various Sarin configurations, the most stable interaction involves the phosphoryl oxygen binding to the metal atoms of TMOs. Our results reveal that the NiO-rGO system is particularly favorable for both P-F and P-OC₃H₇ bond cleavage, with calculated activation energies of -189.8 and -349.27 kJ mol^-1, respectively. This enhanced reactivity is attributed to significant bond polarization and the presence of partially filled Ni 3d⁸ orbitals near the Fermi level, which facilitate both π-back-donation and σ-donation interactions with antibonding orbitals of Sarin. The isopropyl elimination pathway predominantly occurs on CoO-rGO, with an activation energy of -257.15 kJ/mol. The CuO-rGO surface promotes both P-F bond cleavage and isopropyl elimination, with activation energies of -264.07 and -217.5 kJ/mol, respectively. The ZnO-rGO system favors P-OC₃H₇ bond cleavage and isopropyl elimination, with activation barriers of -179.84 and -200.13 kJ/mol, respectively. The Lewis acidity of the TMOs correlates with Sarin decomposition efficiency, with NiO exhibiting the highest positive charge of +1.29 e. Partial density of states revealed a peak of the highest density, indicating an increased density of states for Ni. This work provides valuable insights into the adsorption and decomposition of Sarin, emphasizing the potential of the TMO-rGO system for the breakdown of organophosphorus nerve agents.