Establishing trends in ion adsorption on the aqueous aluminium hydroxide nanoparticle Al30

The fact that chemical reactions at environmental interfaces are becoming accessible to quantum mechanical computational studies provides geochemical researchers with a new means to predict properties that cannot readily be measured and to develop molecular-level understanding of geochemical model systems. Recent computational studies of Cu2+ and [GRAPHICS] adsorption onto the Keggin-based aqueous aluminium nanoparticle ( [GRAPHICS] ), or Al-30, revealed opposing trends in adsorption site preference as a function of molecule surface topology. Specifically, the adsorption site favourable for the inner-sphere adsorption of Cu2+ is on the caps of Al-30 while outer-sphere [GRAPHICS] prefers adsorption in the so-called beltway region of the molecule. When co-adsorbed, it is predicted that both species adsorb in the beltway, consistent with an experimental crystal structure. Here, we discuss results for individual cation and anion adsorption to Al-30. Our goals are to better understand how the adsorbate properties govern interactions with Al-30 and to assess whether generalisations can be formed. We test the reactivity of cations (Cu2+, Pb2+, Zn2+) and anions ( [GRAPHICS] , Cl-) to aqueous Al-30 by using density functional theory modelling. It is determined that all the cations favour the adsorption sites on the caps of Al-30 and both anions favour outer-sphere adsorption in the beltway region. The results are discussed in terms of the electrostatic potential of Al-30 and three-dimensional induced charge density mapping.