Comparative life cycle assessment of different synthesis routes of magnetic nanoparticles

Nanotechnology is the manufacture and use of functional structures that have at least one characteristic dimension measured in nanometers. Among the wide range of applications nanoparticles (NPs) may present, they can be used as a catalyst or as carrier to immobilize biological catalysts, such as enzymes. The use of magnetic nanoparticles (mNPs) presents as main advantage over other alternatives the fact that they can be easily separated by the application of a magnetic field, facilitating their recovery from the reaction medium. In parallel with the increasing interest in the production of nanomaterials, there is a general consensus about their potential health and environmental risks associated. This paper aims to perform the evaluation of different synthesis routes considered for the production of mNPs from a life cycle assessment (LCA) perspective. Specifically, different approaches of mNPs synthesis were evaluated; from simple forms such as sterically-stabilized magnetite and oleic-acid mNPs to production schemes that consider the coating of a shell on the preformed nanoparticles such as PEI-coated mNPs and silica-coated mNPs for the increased stability of the nanoparticle. When merely assessing the outcomes from the LCA study, we observed that the manufacturing stage is dominated by the environmental impacts associated to energy and chemical use, especially relevant for the type of silica-coated mNPs. However, the selection of the optimal support for enzyme immobilization must comply with additional requirements such high immobilization yield. According to the results, a compromise solution for the selection of the support is obtained for PEI-coated mNPs, with satisfactory results in the indicators of enzyme immobilization and limited environmental impact. Moreover, this work highlights two main challenges currently encountered with the application of LCA to nanoproducts: lack of comparable reports and data availability, both imply uncertainties associated with the estimation of the environmental impacts of NPs.