Molecular picture of the adsorption of phenol, toluene, carbon dioxide and water on kaolinite basal surfaces

Volatile Organic Compounds (VOCs) are harmful for both human beings and environment and, consequently their removal from atmosphere by adsorption is one of the most scrutinized techniques owing to its easy implementation as well as its promising results for a wide range of molecules. Kaolinite, one of the most abundant and cheap clay, appears as a good candidate and has already been studied for the removal of various other pollutants such as pharmaceuticals. Here we used first-principles modelling techniques - static Density Functional Theory and Ab Initio Molecular Dynamics to investigate the interaction of kaolinite surfaces with phenol and toluene, two highly dangerous VOCs, as well as of carbon dioxide and water, two abundant atmospheric molecules. We showed that dispersion interactions play an important role in the adsorption mechanisms, especially for the adsorption on the siloxane surface. All the considered molecules preferentially adsorb on the aluminol-terminated surface. Also, we demonstrate that phenol is the most adsorbed molecule on both basal surfaces of kaolinite. On aluminol surface, phenol (-87.1 kJ.mol(-1)) and toluene (-68.2 kJ.mol(-1)) adsorb more strongly than water (-62.4 kJ.mol(-1)) and CO2 (-35.0 kJ.mol(-1)). Therefore, kaolinite could achieve a selective removal of phenol and toluene from air.

Automated summary

Volatile Organic Compounds (VOCs) pose a threat to human beings and the environment, and their removal through adsorption is a widely studied technique. Kaolinite, a common and inexpensive clay, has shown potential for the removal of VOCs. This study used first-principles modelling techniques to investigate the interaction between kaolinite surfaces and VOCs, as well as atmospheric molecules. The results suggest that kaolinite could selectively remove phenol and toluene from the air.