Water Adsorption and Reactions on Small Sodium Chloride Clusters

Abstract

Energetics, structures, and reactions of water with small sodium chloride clusters, Na 4 Cl n , 2 e n e 4, and of OH-doped nonstoichiometric, Na 4 Cl 3 (OH), Na 4 Cl 2 (OH), and Na 4 Cl 2 (OH) 2 , clusters, are investigated employing electronic structure calculations using the local spin-density functional method with exchange-correlation gradient corrections in conjunction with norm-conserving nonlocal pseudopotentials, structural optimizations, and Born-Oppenheimer molecular dynamics simulations. In OH-doped clusters an OH -is formed, substituting for the missing halide anion, and the hydroxyl anion is oriented approximately along the body diagonal of the cuboid structure of the cluster. Energetically and structurally, clusters in the sequence Na 4 Cl 4-m (OH) l with m ) 1, 2 and l e l e m, are similar to the corresponding undoped clusters, Na 4 Cl 4-m+l . On the stoichiometric cuboid Na 4 Cl 4 cluster, a water molecule adsorbs with the molecular plane tilted by ∼13°toward the chlorine anions with respect to the "(100) facet" of the cluster, with a binding energy of ∼0.49 eV. For nonstoichiometric clusters Na 4 Cl n , n ) 2, 3, H 2 O adsorption at the halide-vacant, F-center site, with a binding energy of ∼0.32 eV, is accompanied by partial expulsion of the excess electron from the F-center site. This effect is correlated with a decrease in the vertical and adiabatic ionization potentials upon H 2 O adsorption. The thermochemistry of several reactions of water with alkali chloride clusters is evaluated. The hydrogen generation reaction, Na 4 Cl 2 (H 2 O) 2 f Na 4 Cl 2 (OH) 2 + H 2 , is catalyzed by the surface, with an exothermicity of 2.63 eV, and involving a barrier of 0.33 eV, compared to an exothermicity of 1.22 eV and a barrier of 1.56 eV for the reaction Na 2 (H 2 O) 2 f (NaOH) 2 + H 2 . The mechanism of the cluster-catalyzed reaction is discussed.

Upper consolute temperature of water-phenol systems with some additives

“…The order of TEAB > CPB > CPC > CTAB for UCT and the order of CPC > CTAB > CPB > TEAB for CC, and the order of LDS > SDS for UCT with equal CC values infer the polarizability [19][20][21] of the tetraethyl, cetyl and dodecyl alkyl chains. Four C 2 H 5 -groups cause stronger hydrophobic interactions [20] and an ammonium ion causes hydrophilic interactions resulting in higher UCT and lower CC values where the cetyl and dodecyl alkyl chains of CPC, CPB, CTAB, LDS, and SDS show weaker interactions.…”

“…Therefore, this basicity increases the UCT and CC values by 5.5%, but the equal number of -OH and 2-CH 2 -and 1-CH-of glycerol find UCT trend to be glycerol > 0.4 m urea > 0.6 m urea with a reverse trend for CC values. This weakens the hydrophilic interactions [18,19] of the 3-OH of glycerol, which outweighs those of urea by 0.6% and citric acid by 23.3%.…”

Upper critical solution temperatures for immiscible solvent systems with halide salts, carboxylic acids, surfactants and polynuclear aromatic compounds and benzene derivatives

“…Thus cetyl and dodecyl alkyl chains of CPC, CPB, CTAB, LDS and SDS surfactants show weaker interactions. Lower values of UCST and higher values of CS of surfactants [17,18] than those of salts, acids and aromatic compounds reveal stronger hydrophilic and hydrophobic interactions.…”

Solvation and chemical reaction of sodium in water clusters

“…They suggest a two step mechanism to form Na(NaOH) 2 (H 2 O) n , where first one sodium atom is captured to form Na(H 2 O) n as precursor and then a dimer is attached to the complex to start the reaction. Barnett and Landman [10] found in their calculation of the reaction Na 2 (H 2 O) n → (NaOH) 2 + H 2 has an exothermicity of 1.22 eV and a reaction barrier of 1.56 eV. A decrease of the reaction barrier with increasing cluster size is expected.…”