Adsorption of polyaromatic heterocycles on pyrophyllite surface by means of different theoretical approaches

Abstract

Environmental contextVolatile organic compounds can adsorb to the surfaces of silicates present in atmospheric aerosols, but the mechanisms and interactions are not well understood. We compare theoretical approaches for describing the adsorption of polyaromatic heterocycles to a model phyllosilicate surface. The enthalpy and spectroscopic data for this adsorption provide valuable information for future experimental studies on these atmospheric pollutants. AbstractThe adsorption of thiophene, benzothiophene and dibenzothiophene, as models of polyaromatic heterocycles, on the (001) surface of pyrophyllite, as a model of phyllosilicates, has been investigated by means of empirical interatomic potentials and quantum-mechanical methods based on Hartree–Fock and Density Functional Theory (DFT) approximations. Molecular Dynamic simulations have also been performed for this adsorption, exploring the different configurations that these polyaromatic heterocycles can adopt with respect to the surface. These adsorbates adopt more likely a planar disposition with respect to the phyllosilicate surface. Spectroscopic shifts of the main vibration frequencies upon adsorption of these heterocycles on the phyllosilicate surface have been identified. The adsorption energy calculated with different methods are compared and discussed in terms of adequacy of empirical potentials and DFT methods for describing the weak interactions observed. In addition to considering the (001) surface of pyrophyllite as an external surface of the mineral, the adsorption in the interlayer space was also explored obtaining a d(001) spacing of 12.64 Å. However, the adsorption energy is much lower than the cleavage energy of the interlayer space and it is clear that adsorption is more likely to occur on the external surface than in the interlayer space.