Life Cycle Impact of Titanium Dioxide Nanoparticle Synthesis through Physical, Chemical, and Biological Routes.

The sustainable manufacturing of nanoparticles (NPs) has become critical to reduce life cycle energy use and the associated environmental impact. With the ever-growing production volume, titanium dioxide (TiO2) NPs have been produced through various synthesis routes with differing input materials and reactions, which result in differential reactivity, crystallinity, surface areas, and size distributions. In this study, life cycle assessment is used to analyze and compare the environmental impact of TiO2 NPs produced via seven routes covering physical, chemical, and biological syntheses. The synthesis routes are chosen to represent mainstream NP manufacturing and future trends. Mass-, surface area-, and photocatalytic reactivity-based functional units are selected to evaluate the environmental impact and reflect the corresponding changes. The results show that impact associated with the upstream production of different precursors are dominant for the chemical route. Compared to the chemical route, the physical route requires substantial quantities of supporting gas and high-energy inputs to maintain high temperature; therefore, a higher environmental burden is generated. A high environmental burden is also modeled for the biological route due to the required bacterial culture media. This present study aims to identify the most efficient synthesis route for TiO2 NP production, lower the potential environmental impact, and improve green synthesis and sustainability.