Abstract
The interaction of small organic molecules with chrysotile asbestos surface, Si2Mg3O5(OH)4, was investigated by means of ab initio molecular orbital method, to reveal the specific property of molecular adsorptions on the inorganic surface. We used three kinds of chrysotile models; (i) periodic boundary conditions (PBC) system model, i.e., infinite repeat of Si2Mg3O5(OH)4, (ii) cluster model, i.e., part of PBC model, and (iii) brucite model, i.e., infinite repeat of Mg(OH)2. The geometry optimization for each model was performed by DFT and HF methods with 6-31G(d) basis set. The obtained structural parameters for PBC and cluster models compare well with the experimental data. We estimated the molecular adsorption energies by using the cluster model and small molecules, such as H2O, CH3OH and CH3NH2. We found that the interaction of those molecules with the inorganic surface (with OH group) was equivalent to organic hydrogen bonding: the interaction energy was about 6 kcal/mol for each. It is noteworthy that the electronegative atoms of adsorbing molecules are attractive above OH groups on the surface, while electropositive atoms of adsorbing molecules are attractive above the cavity between positive OH groups. As a result, electropositive as well as electronegative molecules adsorb on chrysotile by electrostatic interaction.
