KCl supported by γ‐Al₂O₃ for selective adsorption of gaseous oxidized mercury: Preparation and adsorption mechanism

The separation of Hg 0 and HgCl 2 with selective adsorbents is crucial for mercury speciation detection. KCl is commonly used but has a limited surface area, a short lifespan, and an unclear mechanism for Hg 0 /HgCl 2 adsorption. Hence, KCl supported by γ‐Al 2 O 3 to create a high‐surface‐area selective adsorbent to enhance practical performance was proposed and the selective adsorption mechanisms of Hg 0 and HgCl 2 through experimental investigations and density functional theory (DFT) calculations were elucidated. Compared to the total breakthrough of pure KCl, that of KCl/γ‐Al 2 O 3 exhibits markedly selective adsorption efficacy on HgCl 2 , with a nearly complete breakthrough rate on Hg 0 at a KCl‐to‐γ‐Al 2 O 3 molar ratio of 1, attributed to their favorable porosity and dispersed active sites. The DFT results verify a weak van der Waals force between KCl and Hg 0 , indicating physisorption, while covalent bonding occurs between KCl and HgCl 2 , suggesting chemisorption. High‐resolution transmission electron microscopy (HRTEM) identifies two crystalline surfaces of 001 and 011 on the developed adsorbent. This clarifies three stable adsorption configurations: 001 Top‐Cl, 011 Top‐Cl, and 011 Cl–Cl bridge, with adsorption energies of −87.11, −110.74, and −174.91 kJ/mol, respectively. Analyses of the electronic structure and interaction region indicator (IRI) reveal that the Hg atom within HgCl 2 forms covalent bonds with unsaturated Cl atoms on the KCl surface. Additionally, integrated crystal orbital Hamilton population (ICOHP) analysis and electron transfer results demonstrate that the interaction strength of the three configurations with HgCl 2 follows the order of 011 Cl–Cl bridge > 011 Top‐Cl > 001 Top‐Cl. This matches the three different temperature peaks of 276, 231, and 120°C, respectively, in the analysis of the temperature‐programmed desorption of HgCl 2 (HgCl 2 ‐TPD). This study offers a novel insight on mercury speciation partitioning between Hg 0 and HgCl 2 .