(548k) Electronic Waste to Nanoparticles: Influence of Precursor Purity on Nanoparticle Synthesis

The synthesis of gold nanoparticles typically uses a 99.9% pure gold chloride precursor. However, natural resources of precious metals, such as gold, are in a deficit and estimates project depletion in the next 50 years. With high concentrations of precious metals contained in electronic waste, recycled e-waste can serve as an alternate source. To minimize the waste generated during the refining of metals stripped from e-waste, we explored the potential to synthesize gold nanoparticles using a mixed metal precursor solution where gold was not the dominate species. The mixtures tested included binary mixtures of gold and copper or gold and nickel, as well as a ternary mixture of gold, copper, and nickel. Varying molar ratios (1:1 to 1:25) of gold to copper and/or nickel were prepared for gold nanoparticle synthesis by two widely used methods, the Turkevich method and sodium borohydride chemical reduction method. It was determined that gold nanoparticles formed without aggregation at ratios up to 1:2 gold to copper/nickel for both reducing agents. This also translated to the ternary mixture with the formation of gold nanoparticles up to a ratio of 1:1:1 gold to copper to nickel. Calculating the E-factor and other green chemistry metrics suggest that the Turkevich method is less waste generating compared to the sodium borohydride chemical reduction method. The results of this study demonstrate that lower purity gold precursors can still produce gold nanoparticles suggesting that use of alternate sources of gold and/or less separations steps are viable routes to reducing the environmental impact of gold nanoparticle synthesis.