Reprinted with permission from J. Phys. Chem. C, 2017, 33, pp 1412-1418. Copyright 2017 American Chemical Society.

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.

Ahmet Uysal1 , William Rock1Baofu Qiao1Wei Bu2, and Binhua Lin2

1Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States

2Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, United States

J. Phys. Chem. C, 2017, 121, pp 25377–25383

DOI: 10.1021/acs.jpcc.7b09350