(166e) Process Optimization for the Synthesis of Gold and Copper Nanoparticles from a Mixed Precursor Solution

Separation methods involving a mixture of metals typically include upfront processing that leads to one final product. To lower the waste and ultimately environmental burden, we explore the potential to synthesize multiple functional products from a mixed metal precursor solution. Specifically, our initial precursor solution contained varying ratios of gold and copper ions. The amount of gold was kept constant, while the amount of copper was sequentially increased. Two separate synthesis processes were tested, the traditional Turkevich method involving sodium citrate and another chemical reduction method involving sodium borohydride. The particle size and chemical composition of the synthesized particles were characterized using TEM, EDX, and ICP-OES. Preliminary results suggest that the Turkevich synthesis limit in which gold nanoparticles no longer form is between a molar ratio of 2 to 10 times more copper to gold. In comparison, when sodium borohydride is used as a reducing agent, the gold nanoparticle formation limit is between an equimolar ratio and a molar ratio of 5 times more copper to gold. These results suggest the stronger reducing agent is still allowing particle formation to take place. Currently, EDX is being used to study the composition of the particles produced by both reducing agents to understand how to optimize the process. In addition to precursor metal concentrations, the influence of other variables such as pH and ionic strength on the synthesis of gold and/or copper nanoparticles are being investigated. A comparison of the green chemistry metrics calculated for the optimized reactions revealed similar with upfront separation or use of additional reagents versus the conventional synthesis reactions to create gold and copper nanoparticles will be presented. Initial calculations quantify an E factor of around 35 for the reaction using sodium borohydride as the reducing agent. This is compared to an E factor of around 26 for the reaction using sodium citrate as the reducing agent.