Study of Surface Morphology Effects on Hg Sorption–Desorption Kinetics on Gold Thin-Films

Mercury (Hg) vapor sorption and desorption kinetics on gold (Au) thin-films of different surface morphologies and at various operating temperatures have been studied by using the quartz crystal microbalance (QCM) technique. The QCM data was used to estimate Hg desorption activation energy ( E a ) from Au nanostructured surfaces deposited over optically polished (Au-polished) and mechanically roughened (Au-rough) quartz substrates to better understand Hg adsorption and desorption processes, with the ultimate aim of developing better materials for Hg measurement and/or capturing applications. After accounting for the difference in active surface area, the Au-polished sample was calculated to have a Hg uptake of ∼1030 ng·cm –2 when exposed to 10.55 mg·m –3 of Hg vapor for 1 h. In comparison, the Au-polished film had a Hg uptake 15% higher than that of the Au-rough film at an operating temperature of 28 °C. However, at 132 °C, the difference increased to ∼140% higher uptake for the Au-polished film, thus indicating that each surface exhibits a different Hg–Au sticking probability which is temperature dependent. In the case of the desorption process, it was found that a higher energy is required to release the Hg from the Au-rough surface compared to that of the Au-polished surface, per unit of surface area. The mechanism was found to initially be first order for the adsorbed Hg atoms at the surface and thereafter a second-order kinetic where the absorbed/diffused Hg atoms from the bulk of the film are released.