Heavy metals are typically removed from industrial point-sources by physical removal of bulk material, allowing dissolved ions to pass through. Modifying these filters to include chelating functional groups presents an opportunity to increase filter efficiency. Melanin has been shown to bind non-specifically to a variety of metal ions, and is easily bound to silica, a common filtration material. In this study, melanin shells were synthesized around bare silica nanoparticles following a published method. The resulting silica/melanin particles were characterized, and their affinity for a heavy metal ion, silver, was compared to that of commercially available melanin (<i>Sepia officinalis</i>). Zeta potential vs. pH titrations (Figure 1a) show that the behavior of silica particles shifts closer to commercial melanin after shell synthesis, confirming surface coverage by the melanin. UV-Visible and infrared spectroscopy also show evidence of melanin absorption peaks after coating (data not shown). To determine binding affinity, suspensions of melanin and silica/melanin particles (5 ppm) were incubated with 5 ppb silver at pH 7, while a control sample contained 5 ppb silver at pH 7 with no melanin. The suspensions were centrifuged to pellet the melanin and the resulting supernatants analyzed by ICP-MS to determine the concentration of silver remaining in solution (Figure 1b). Silica/melanin reduced the concentration of silver by 50% compared to the positive control, while commercial melanin reduced the concentration by 77%. These results indicate melanin coated silica may be effective for dissolved heavy metal removal with further optimizations. Subsequent studies will expand this concept to other metals of interest including mercury, tin, and copper.

Silver binding affinity of silica/melanin nanoparticles

253rd National Meeting (2017)

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