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 μm 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 [Hg²⁺, methylmercury (MeHg⁺), 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 MeHg⁺ ions from water. The low-cost, effective, and stable Au NP–Al₂O₃ adsorbent shows great potential for economical removal of various mercury species.