Supercritical Fluid Flow Synthesis to Support Sustainable Production of Engineered Nanomaterials: Case Study of Titanium Dioxide

Abstract

Supercritical fluid flow synthesis exploits unique properties of solvents in order to achieve reactions that proceed quickly to produce high-quality nanocrystals. Supercritical fluids are often referred to “green” solvents because they can proceed at moderate temperatures. Therefore, this study sought to compare the supercritical fluid flow synthesis of TiO2 to that of a conventional precipitation method from an environmental and human health perspective. A life-cycle assessment was conducted to determine the impacts of producing 1 kg of dry TiO2 nanoparticles using either the supercritical or precipitation route. While the results suggest that supercritical fluid flow synthesis may indeed be a preferable synthesis route compared with a conventional route such as precipitation, the inherent uncertainty underlying this emerging technology indicates that there are a number of trade-offs in switching from one technology to another. Supercritical fluid flow synthesis was likely a better technology option from a cumulative energy demand and climate change perspective; however, there was less evidence for this from a human health and ecotoxicological perspective, for example. In particular, occupational exposure to emissions of TiO2 nanoparticles could be an issue for this emerging industry if the proper protective controls are not put in place.