Comparative life cycle assessment of silver nanoparticle synthesis routes

Silver nanoparticles (AgNPs) can be produced through a variety of synthesis routes with differing mechanisms, inputs, yields, reaction conditions, and resulting size distributions. Recent work has focused on applying green chemistry and sustainable manufacturing principles to nanomaterial synthesis, with the goal of reducing life cycle energy use and environmental impacts. Life cycle assessment (LCA) is used here to analyze and compare the environmental impacts of AgNPs produced through seven different synthesis routes (cradle-to-gate). LCA reveals both direct and indirect or upstream impacts associated with AgNPs. Synthesis routes were chosen to represent current trends in nanoparticle synthesis and include physical, chemical and bio-based methods of production. Results show that, across synthesis routes, impacts associated with the upstream production of bulk silver itself were dominant for nearly every category of environmental impact, contributing to over 90% of life cycle burdens in some cases. Flame spray methods were shown to have the highest impacts while chemical reduction methods were generally preferred when AgNPs were compared on a mass basis. The bio-based chemical reduction route was found to have important tradeoffs in ozone depletion potential and ecotoxicity. Rescaling results by the size-dependent antimicrobial efficacy that reflects the actual function of AgNPs in most products provided a performance-based comparison and changed the rank order of preference in every impact category. Comparative results were also presented in the context of a nanosilver-doped wound dressing, showing that the overall environmental burdens of the product were highly sensitive to the synthesis route by which the AgNPs are produced.