A surface second harmonic generation investigation of volatile organic compound adsorption on a liquid mercury surface

Abstract

Understanding the adsorption process of volatile organic compounds (VOCs) on various surfaces is essential in the realms of atmospheric, environmental and pollution remediation science. In this study, we investigated the adsorption of selected VOCs (benzene and toluene) on an ideally homogeneous liquid mercury (Hg_(l)) surface using a surface sensitive nonlinear spectroscopic method of second harmonic generation (SHG). Both of the species investigated showed evidence of reversible physisorption. Determination of SHG adsorption isotherms revealed that attractive adsorbate–adsorbate lateral interaction plays a role in the adsorption of aromatic compounds from the gas phase. Benzene and toluene adsorption has been described by the Hill-de-Boer (HdB) adsorption isotherm model with the corresponding HdB interaction parameters, 2α/β, of 2.6 ± 0.2 and 3.3 ± 0.2 kcal mol⁻¹, respectively. Our results highlight the importance of lateral interactions between adsorbed aromatic species at the gas/liquid interfaces. The investigation extends the applicability of SHG to probe complex adsorption processes under ambient conditions.