Direct Ag-Hg amalgamation in the nanoscale on the surface of biosourced amorphous silica

Mercury poses a significant threat to air, soil, and water ecosystems. Mercury-based alloys, aka amalgams, are already known for their effectiveness in mercury capture in water and gaseous streams. However, limited research has been published on direct amalgamation, the process involving a direct redox reaction between two metals, occurring on the surface of amorphous silica. This study investigates the amalgamation process in nanoscale, in particular the direct interaction between silver (Ag⁰) nanoparticles supported on functionalized bio-derived amorphous silicon dioxide (SiO₂) and mercury (Hg^2⁺) ions in aqueous solutions. Also, the influence of aqueous mercury speciation on amalgamation is studied in detail. The results reveal that the presence of chloride (Cl⁻), acetate (OAc⁻), and nitrate (NO₃⁻) ions significantly influences the interaction between mercury and silver. We propose plausible mechanisms to explain these observations. Our findings demonstrate that the maximum mercury uptake capacity followed the order HgCl₂ > Hg(OAc)₂ > Hg(NO₃)₂, while the reaction rate followed the order Hg(OAc)₂ > HgCl₂ > Hg(NO₃)₂. These findings hold significant implications for the design of efficient mercury remediation processes. By elucidating the influence of aqueous speciation on amalgamation, our work paves the way for tailored strategies that can maximize mercury capture from water.