Colloidal gold nanoparticles (Au NPs) have been employed as single entities for rapid scanning and sequestration of Hg(II) from multicomponent aqueous solutions containing low pollutant concentrations. Under the studied conditions, sodium citrate has been identified as the reducing agent and Au NPs as the catalyst in the reduction of Hg(II), which is efficiently trapped in the presence of other cations such as Cu(II) and Fe(III). The effect of Hg(II) uptake implies amalgam formation, which leads to remarkable morphological transformations. The hydrophobicity of the resulting amalgam and consequent expulsion from water eases its recovery. The interaction between Au and Hg has been studied using UV-vis, ICP-MS, (S)TEM, SEM, EDX, and XRD.

Cr ion-polluted industrial water was treated with commercial activated carbon and with either mercaptane- and amine-functionallized silica nanoparticles, revealing that the use of relatively low surface area materials can advantageously compete with high surface area materials, traditionally utilized for removing hazardous metal ions, provided a proper surface functionalization of the nanoparticles is in place. FTIR and SEM characterization of the different materials and stages of the experiments are provided, as well.