First principles studies of water and ice on oxide surfaces

• Main Author: Hu, X.
• Published: University College London (University of London) 2010
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564900

The interaction of water (and ice) with oxide surfaces has been studied with first principles density functional theory. To begin, an extensive series of studies on the clay mineral kaolinite (Al_2Si_2O_5(OH)_4) are reported with a view to understanding the efficacy of kaolinite as a heterogeneous ice nucleating agent. The main conclusions are: (i) water clustering is disfavoured on the kaolinite surface; (ii) a stable two dimensional ice-like water overlayer can form; (iii) water covered kaolinite is itself “hydrophobic” compared to the bare “hydrophilic” kaolinite surface; and (iv) it is shown that amphoterism (the ability to accept and donate H bonds) of the hydroxylated kaolinite surface is key to its many properties with regard to water adsorption and ice nucleation. Following the water adsorption study, the perfect basal surface of kaolinite was investigated and it (and in general the entire class of so-called 1:1 clay surfaces) is shown to be polar. Extending the water adsorption studies beyond kaolinite the interaction of water with a range of rocksalt (alkaline earth metal) oxide surfaces was examined with a view to better understanding the fundamental properties of water adsorption, dissociation, and proton transfer on oxide surfaces. These studies reveal that the water adsorption energy and the tendency to dissociate both increase as one moves down the alkaline earth series of oxides. Finally, it is observed that water on MgO(001) undergoes rapid proton transfer within clusters of just two water molecules, made possible by facile dissociation and recombination of the water molecules within the dimers. Overall, it is hoped that these studies shed new light on several fundamental aspects of the interaction of water with oxide surfaces at the molecular level.