Scavenging activity of Magnéli phases as a function of Ti4+/Ti3+ ratios

Abstract

TiO₂ is able to scavenge reactive oxygen and nitrogen species (ROS and RNS) in the absence of light. The scavenging mechanism has been related to the chemistry of defects (oxygen vacancy reduced oxidation states of Ti) but it is still unknown. This study describes the ROS scavenging activity of different titanium oxide phases and relates their scavenging activities with the Ti⁴⁺/Ti³⁺ molar ratio as well as the band gap value. The Ti₅O₉ phase, with a mixture of both oxidation states, presented a substantially higher percentage of 2,2-diphenyl-1-picrylhydracyl radicals (DPPH˙) eliminated per m² of specific surface area in comparison to phases with predominant oxidation states Ti⁴⁺ or Ti³⁺ such as TiO₂ and Ti₂O₃, respectively. The obtained results indicate that the DPPH˙ scavenging mechanism corresponds to a catalytic process on the Ti₅O₉ surface which is facilitated by the presence of charges that can easily move through the material. The mobility of charges and electrons in the semiconductor surface, related to the presence of oxidation states Ti⁴⁺ and Ti³⁺ and a small band gap, could create an attractive surface for radical species such as DPPH˙. This puts forward Ti₅O₉ as a promising candidate coating for implantable biomedical devices, as an electrode, since it can cushion inflammatory processes which could lead to device encapsulation and, consequently, failure.