(643h) The Binding of Hg on Pd Binary Alloys and Monolayers
Many sorbent materials such as activated carbon, metal oxides, metal sulfides and pure metals can capture mercury under specific conditions. Among these materials activated carbon is one of the most-used sorbents due to its high removal capacity. Unfortunately, it has been reported that activated carbon can prevent concrete from meeting the freeze-thaw requirements in the recycling step involving the addition of particulate matter for concrete manufacturing. It would be much more efficient to use a material that is proficient at removing mercury and also concrete-friendly.
Density Functional Theory (DFT) calculations have been performed to predict the binding mechanism of element mercury on the binary alloys PdAu(111), PdAg(111), PdCu(111). The Pd surface has been found to be more reactive than the Au, Ag and Cu surfaces, although small additions of Au, Ag and Cu to bulk Pd surface increases the overall mercury binding energy. Specifically, it has been found that Au atoms in the PdAu alloys are most beneficial to Hg adsorption when they remain below the surface layer. This prompted studies using a monolayer of Pd overlayed on an Au substrate to further enhance binding compared to the PdAu alloys. The use of monolayers not only removes the dependence on the random atomic arrangement, but it may also lead to a higher capacity because of the surface composition uniformity and subsequent increased number of binding sites.