Interfacial activity of nitric acid at the water–supercritical CO2 interface: a molecular dynamics investigation

Abstract

We report a molecular dynamics study on a nitric acid water–supercritical CO₂ interface. Three extreme models are compared, where the acid is either all neutral HNO₃, completely dissociated into NO₃⁻ and H₃O⁺, or represented by a 1 : 1 mixture of both forms. The ionic species are found to be “repelled” by the neat interface, while the neutral HNO₃ molecules are highly surface active. Similar features are observed with SC-CO₂ or with chloroform as the organic phase, pointing to the generality of interfacial activity of the acid.