Silica matrix encapsulation as a strategy to control ROS production while preserving photoreactivity in nano-TiO2

In this work, the application of a silica coating on TiO2 nanoparticles (NPs) represented a material design strategy for the purpose of controlling the reactive oxygen species (ROS) production, identified as one of the potentially hazardous effects for this class of materials. The study focused on characterizing redox reactivity as a source of potential adverse cellular oxidative stress and desirable photocatalytic reactivity. The SiO2-modified TiO2 systems were produced using a colloidal heterocoagulation method expected to give rise to "matrix encapsulation" and the formation of a mixed structure. To assess the effect of SiO2 surface engineering on TiO2 NP redox reactivity, ROS production was measured by electron paramagnetic resonance (EPR) and photocatalytic tests based on NOx/NO abatement analysis were carried out. The obtained reduction in ROS production associated with an improved photoactivity in the SiO2-modified samples, in comparison with the TiO2 pristine ones, encouraged the promotion of silica coating as "safer by molecular design" strategy.