title: Theoretical study of the reaction between HF molecules and hydroxyl layers of Mg(OH)2.
abstract: The reaction of HF molecules with brucite, Mg(OH)(2), leading to the formation of Mg(OH)(2-x)F(x), was theoretically studied by ab initio density functional theory (DFT) with periodic boundary conditions. We proposed as mechanism for this reaction four elementary steps: adsorption of the HF molecule, OH(-) liberation from brucite as a water molecule, desorption of the newly formed H(2)O, and rearrangement of the F(-) anion into a hydroxyl position. For the Mg(OH)(2-x)F(x) formation, with x = 1/9, the final product, outcome from an initially adsorbed HF molecule, we computed the Helmholtz free energy variation DeltaF = -23 kcal/mol. The calculated frequency for the most intense infrared band, a Mg-F stretching mode, was 342 cm(-1). Two transition states, corresponding to the hydroxyl reacting with a proton forming a water molecule and migration of a fluoride anion into a hydroxyl vacancy, were computed. The calculated reaction barriers indicate that the reaction between Mg(OH)(2) layers and HF molecules is slow and irreversible.
authors.affiliation: Departamento de Química, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, 36036-330, Brazil.
authors.forename: Viviane S
authors.initials: VS
authors.lastname: Vaiss
authors.forename: Rafael A
authors.initials: RA
authors.lastname: Berg
authors.forename: Ary R
authors.initials: AR
authors.lastname: Ferreira
authors.forename: Itamar
authors.initials: I
authors.lastname: Borges
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Leitão