Adsorption Of Fullerene On Clay Mineral Surface: Molecular Modeling Study

As the nanomaterials are widely used in the fields of electronics, environmental protection, medicine and energy development, etc. A variety of man-made nanomaterials emission into the environmental media inevitably through many channels and generate significant ecological deleterious effects, so the environmental chemical action of nanomaterials has gained much attention. Clay minerals as a rich geosorbent in the nature, has a special layered structure and physicochemical properties, which has important influence on the migration, concentration and pollution control process of the pollutants in the environment. Therefore, the study of interaction between nanoparticles and the surface/interface of clay mineral can make clear about the environmental chemical behavior of nanomaterials. This paper uses simulation technology to investigate the effect of the interaction between buckminsterfullerene(C60) and the clay mineral by the surface structure and hydration status of clay mineral, especially the information of adsorption sites of the clay mineral’s surface/interface, adsorption energy and occurring states. The research results are as follow:(1) The equilibrium arrangement of C60 molecules on pyrophyllite layer tends to be monolayer. The result shows that C60 molecules can spontaneously be adsorbed on the siloxane surface of pyrophyllite in a vacuum and the most stable adsorption site is the ditrigonal cavity of the surface. Increasing C60 molecules into the system gradually, they tend to the monolayer arrangement. The free energy of the adsorption on pyrophyllite is calculated that along with the increasing number of C60 molecules, the free energy minima of the adsorption becomes reductive. It suggests that the sorption acting on the single C60 molecule increases.(2) In the aqueous environment, the surface of pyrophyllite has an affinity with C60 molecules, but C60 molecules should get rid of the hydration layer during the adsorption process and form the energy barriers. Although pyrophyllite and C60 molecules are both hydrophobic material, around C60 molecules will appear hydration layer because of the strong van der waals forces between C60 molecules and water molecules. Hence, there are energy barriers as the C60 molecule approaches the pyrophyllite surface, and these occur upon disruption of the hydration layers. In motion to neighboring pyrophyllite the C60 molecule may adsorb into the ditrigonal cavity of the surface to be a stable adsorption state. The calculation indicates that along with the increasing number of C60 molecules, the free energy minima of the adsorption becomes reductive.(3) Due to the strong hydration of the hydroxyl surface, it is difficult to adsorb C60 molecules effectively. The calculation results show that C60 molecules can be adsorbed on the hydroxyl surface in a vacuum, but the adsorption capacity of hydroxyl surface is weaker than the si-loxane surface. The hydroxyl groups on the kaolinite surface have a strong interaction with the water molecules in aqueous environment and a dense layer of water molecules is formed on the kaolinite surface, it has a negative effect on the adsorption of C60 molecules. As the free energy minima of different amount(1-3) of C60 molecules respectively is-0.096 e V,-0.110 e V and-0.136 e V, it proves that the amount increases and the free energy minima decreases. There are energy barriers and the local minimum free energy appearing in the adsorption process, we infer that the kaolinite layer, C60 molecules and water molecules form a complex system, and the C60 molecules should constantly disrupt the hydration layers that surround each component.