Towards the development of a safer by design mineral photocatalytic paint: influence of the TiO2 modifications on particle release†

The development of safe nanomaterials has become a significant concern in various industry sectors using advanced materials. While there is variability in the definitions of Safe(r) by Design (SbD), the general concept is to minimise environmental, health and safety concerns by implementing appropriate measures at an early stage of product design to control exposure and hazard, thus reducing risks. The SbD product strategy applied in this paper refers to the mitigation of exposure by the identification of release scenarios during the use and the end of life of nano-enabled products (NEPs) that include engineered nanomaterials (ENMs). This strategy was applied to the development of a photocatalytic mineral paint containing a TiO₂ engineered nanomaterial. This ENM was then incorporated into a mineral matrix-based paint for photocatalytic application. The different paint formulations were applied to standardised substrates and artificially weathered in an accelerated weathering chamber with controlled parameters. Mechanical solicitation that simulates the end of life (EoL) of the paint, through abrasion tests, was performed to assess the potential emission of airborne particles that could lead to human or environmental exposure. The release evaluation confirms that paints with TiO₂ nanoparticles without SbD coating release more nanometric particles due to strong matrix degradation. TiO₂ nanoparticles coated with PEG or grafted onto CNCs do not completely prevent the degradation of the paint surface during ageing. However, this degradation does not necessarily lead to an increase in aerosol emission. The coating degradation during accelerated ageing limits the degradation of the paint matrix, preventing the release of unbound TiO₂ nanoparticles. Understanding the mechanisms of release and how they are influenced by ENMs, the matrix material and the process characteristics are crucial for the exposure and risk assessment approach in occupational settings involving engineered nanomaterials. Moreover, establishing release rates makes it possible to increase the reliability of SbD e-infrastructure for performance testing and the implementation of Safe-by-Design approaches in the nanotechnology supply chain.