Titanium dioxide catalytic activity contributes to the process of free radical scavenging

Abstract

TiO2 crystallochemical properties have been explored and correlated with the activity of this material in the scavenging of reactive oxygen and nitrogen species (ROS/RNS). It is well known that those highly reactive species are produced by inflammatory cells and neutralized by some oxides, such a titanium dioxide under light. Nevertheless, the mechanism of action of this ceramic material is yet to be fully understood. A set of reactions have been proposed that imply the presence of different valence states of titanium as the basis for the ROS/RNS scavenging, but in this work, we have demonstrated that those species are not always detected in TiO2-based materials, which are, in addition, active in depleting ROS/RNS. TiO2 powders with undetected Ti3+ have been obtained with a range of different properties—surface area, particle size, rutile–anatase ratio, and band gap values—by varying the powder processing conditions after synthesis through the sol precipitation route. The properties of the powders have been correlated with the scavenging activity of the materials toward two reactive species, DPPH· and peroxynitrite, always conducted under dark conditions. It was observed that despite the lack of Ti3+ states, TiO2 powders can still neutralize ROS/RNS. For the first time, this study explain how the catalytic activity of different TiO2 contribute to the free radical scavenging mechanism and the differences in scavenger activity shown by different TiO2 phases and mixtures.