Adsorption of Benzene on Hematite Surfaces: A van der Waals corrected DFT Study

LUIS G. AQUINO LINAREZ; CAROLINA ZUBIETA; SILVIA A. FUENTE; PATRICIA G. BELELLI; RICARDO M. FERULLO

Santa Fe

Congreso; VI San Luis Congress of Surfaces, Interfaces and Catalysis; 2018

Universidad Nacional del Litoral

In this work, we have studied the interaction of benzene with clean and hydroxylated surfaces of hematite using a quantum-chemical method. The (0001) surface is the dominant face in natural and synthetic hematite. There are different ways of finishing this surface. The single Fe-terminated is the most stable under UHV conditions. Under water exposure, hydroxylated surfaces are formed, being the most stable that one composed by a layer of hydroxyl groups on an Fe bilayer. We have modeled both surfaces with symmetric slabs. The corresponding 2 × 2 cells contain 80 and 116 atoms for the clean and hydroxylated surfaces, respectively. On the clean Fe-terminated (0001) surface, benzene adsorbs strongly in two different modes with the same adsorption energy (-1.05 eV). In both, the molecule is almost parallel to the surface and they only differ on the way they are oriented. In both cases, one C atom of benzene is located on top over a protruding Fe ion (with C-Fe distances of 2.37 and 2.40 A, respectively) and with the molecule slightly tilted (around 6 degrees) with respect to the surface. These geometries are quite different to those ones obtained using empirical vdW corrections. In comparison, the value of the adsorption energy calculated here using optB86b for benzene/hematite is larger in magnitude than those computed for benzene adsorption on Cu(111), Ag(111) and Au(111) using the same functional. On the hydroxylated hematite surface, the benzene molecule adsorbs more weakly, with an adsorption energy of -0.53 eV. In this case, the aromatic ring is oriented parallel to the surface with a closest C-H (of OH) distance of 2.49 Å. The results are analyzed by calculating atomic charges, magnetizations and projected density of states.