Environmental assessment of different processing methods for the synthesis of TiO2 nanoparticles

Engineered nanomaterials are increasingly gaining a worldwide relevance in a plenty of high-technological applications. Due to the yet completely un-established environment and human health impact of nanomaterials, the possibility to choose the greener synthetic route through accurate comparison of their environmental impact quantitative assessment, will soon become of absolute importance in both small as well as large-scale production of these advanced inorganic materials. In this last perspective, among the key issues related to minimisation of the impact of nanotechnology on the environmental and on the human health, life cycle assessment and green chemistry metrics in general have been reported as mandatory. In this work green metrics assessment of different synthesis of titanium dioxide (TiO2) nanoparticles have been performed by following two different approaches, namely by using EATOS software [1] and by Life Cycle Assessment (LCA) methodology [2]. The choice of TiO2 is due to the fact that it is the most studied and applied semiconductor and photocatalyst, as a consequence of its unique physicochemical properties [3]. Particularly nanosized anatase is the most attractive crystalline form of TiO2 for advanced and high-technological applications mainly because of its higher stability and photocatalytic activity with respect to rutile and brookite. Consequently, the obtainment of anatase nanoparticles with high purity and precisely controlled structure and particle size is the main purpose of optimized synthetic methods. Several methods have been developed over the last decade to achieve this scope; in particular, this work will consider the most widely diffused synthetic strategy according to the scientific literature, such as hydrolytic sol-gel [4], hydrothermal [5] and solution combustion [6] synthesis processes. Moreover, the use of alternative or at least less conventional heating techniques will be considered as well. In details, the here performed LCA studies followed an ecodesign approach, in order to limit the environmental impacts and to protect the human health. The analysis of the results were performed by using the SimaPro 8.0.2 software and IMPACT 2002+ method, which has been modified introducing a preliminary attempt to assess the TiO2 nanoparticles toxicity released in water on both freshwater ecosystem and humans. As concern the software EATOS, it has been employed to calculate the environmental parameters, which account for the environmental costs related to all the chemicals involved in the analyzed syntheses. This free of charge software allows utilization of easily available data for the calculation of green metrics indexes. The results of the environmental comparison performed among the analyzed syntheses of TiO2 nanoparticles highlighted the great potentialities of EATOS-LCA combination also in the inorganic chemistry field, allowing defining the greener option available to inorganic chemists and materials scientists