Water adsorption on α-V2O5 surface and absorption in V2O5∙nH2O xerogel: DFT study of electronic structure.

Adsorption of water on (001)-terminated α-V 2 O 5 surface has been investigated in the framework of density functional theory. According to our calculations, molecular adsorption is preferred, and two types of adsorption sites (Lewis acid center on V atom and Lewis base center on O atoms) have been found. Water adsorption on Lewis acid site does not change the electronic structure of V 2 O 5 surface. Adsorption on Lewis base site is less favorable but reduces the band gap value by half (from 2.5 to 1.3 eV). The reason of this decreasing is the localization of the non-bonding 1 b 2 electron state of water molecule within the forbidden gap of V 2 O 5 surface. The idealized structure of V 2 O 5 ∙ n H 2 O xerogel has been computationally studied at n  = 0 and 1. It is proved that only Lewis base sites are suitable for water positions. At n  = 1, the water absorption energy in xerogel is close to adsorption energy of water on the oxygen atoms of α-V 2 O 5 surface. The presence of the non-bonding states of physically absorbed water in the forbidden gap is also found in the xerogel case. This results in decreasing of the band gap from 2.7 eV to 0.7 eV. [ABSTRACT FROM AUTHOR]