Gold Nanoparticle-Aluminum Oxide Adsorbent for Efficient Removal of Mercury Species from Natural Waters

We report a new adsorbent for removal of mercury species. By mixing Au nanoparticles (NPs) 13 nm in diameter with aluminum oxide (Al2O3) particles 50-200 mu m in diameter, Au NP-Al2O3 adsorbents are easily prepared. Three adsorbents, Al2O3, Au NPs, and Au NP-Al2O3, were tested for removal of mercury species [He, methylmercury (Me He), ethylmercury (EtHg+), and phenylmercury (PhHg+)]. The Au NP adsorbent has a higher binding affinity (dissociation constant; K-d = 0.3 nM) for Hg2+ ions than the Al2O3 adsorbent (K-d = 52.9 nM). The Au NP-Al2O3 adsorbent has a higher affinity for mercury species and other tested metal ions than the Al2O3 and Au NP adsorbents. The Au NP-Al2O3 adsorbent provides a synergic effect and, thus, is effective for removal of most tested metal ions and organic mercury species. After preconcentration of mercury ions by an Au NP-Al2O3 adsorbent, analysis of mercury ions down to the subppq level in aqueous solution was performed by inductively coupled plasma mass spectrometry (ICP-MS). The Au NP-Al2O3 adsorbent allows effective removal of mercury species spiked in lake water, groundwater, and seawater with efficiencies greater than 97%. We also used Al2O3 and Au NP Al2O3 adsorbents sequentially for selectively removing Hg2+ and Me Hg+ ions from water. The low-cost, effective, and stable Au NP-Al2O3 adsorbent shows great potential for economical removal of various mercury species.