Unprecedented Selectivity and Rapid Uptake of CuS Nanostructures toward Hg(II) Ions

Fast, selective, and effective enrichment is critical for onsite detection and online monitoring of extremely low-concentration toxic heavy metal ions in complex environmental samples. In the current work, varied CuS nanostructures (hollow nanospheres, nanoflowers, nanoparticles) were prepared and applied to the enrichment of Hg(II) ions. Surprisingly, the as-prepared CuS nanostructures exhibited unprecedented ultrahigh selectivity and rapid uptake toward Hg(II) ions in the presence of other seven metal ions, suggesting specificity of mercury enrichment by the CuS nanostructures. Upon treating a 100 mL aqueous sample containing 8 different metal ions with only 10 mg of CuS hollow nanospheres, over 99.5% of Hg(II) ions could be removed within just 1 min, achieving a final Hg(II) ion level down to 0.1 ppb. This excellent selectivity was well accounted for by the Hard Soft Acid Base theory and especially the solubility product constant, where the solubility product constant of CuS is higher than that of HgS but lower than that of sulfides of other interfering metal ions. The current results are striking and would open a new avenue to the search for highly selective and efficient absorptive nanomaterials toward varied heavy metal ions.