posted on 2017-11-30, 19:24authored byAhmet Uysal, William Rock, Baofu Qiao, Wei Bu, Binhua Lin
Anion
exchange at positively charged interfaces plays an important
role in a variety of physical and chemical processes. However, the
molecular-scale details of these processes, especially with heavy
and large anionic complexes, are not well-understood. We studied the
adsorption of PtCl62– anionic complexes
to floating DPTAP monolayers in the presence of excess Cl– as a function of the bulk chlorometalate concentration. This system
aims to simulate the industrial conditions for heavy metal separations
with solvent extraction. In situ X-ray scattering and fluorescence
measurements, which are element and depth sensitive, show that the
chlorometalate ions only adsorb in the diffuse layer at lower concentrations,
while they adsorb predominantly in the Stern layer at higher concentrations.
The response of DPTAP molecules to the adsorbed ions is determined
independently by grazing incidence X-ray diffraction and supports
this picture. Molecular dynamics simulations further elucidate the
nanoscale structure of the interfacial complexes. The results suggest
that ion hydration and ion–ion correlations play a key role
in the competitive adsorption process.