Chemical scanning of atomic oxygen at the gas-liquid interface of a NaCl solution via quantum mechanics/molecular mechanics molecular dynamics simulations

Abstract

Atmospheric pressure plasmas can serve as double phase reactors to produce plasma activated water for water treatment. However, the physical-chemical processes involving plasma-supplied atomic oxygen and reactive oxygen species in an aqueous solution remain unclear. In this work, quantum mechanics (QM)/molecular mechanics (MM) molecular dynamics simulations (MDs) have been performed to directly observe the chemical reactions occurring between atomic oxygen and a NaCl solution at the gas-liquid interface using a model containing 10,800 atoms. During simulations, the atoms in the QM and MM Parts are dynamically adjusted. To examine the effects of local microenvironments on the chemical processes, atomic oxygen is used as a chemical probe to scan the gas-liquid interface. The excited atomic oxygen reacts with water molecules and Cl− ions to produce H2O2, OH, HOCl, ClO−, and HO2−/H3O+ species. The ground-state atomic oxygen is significantly more stable than the excited atomic oxygen, although it can react with water molecules to produce OH radicals. However, the branch ratio of ClO− computed for triplet atomic oxygen is significantly larger than that determined for singlet atomic oxygen. This study can help achieve a better understanding of the fundamental chemical processes during plasma-treated solution experiments and promotes advances in applications of QM/MM calculations at the gas-liquid interface.