A Nitrogen- and Self-Doped Titania Coating Enables the On-Demand Release of Free Radical Species.

For potential applications such as suppressing the onset of peri-implant infections, a doped titania coating was developed to induce free radical release because of its ability for microbial elimination. The coatability of the sol-gel precursor is robust since the suspension's rheology can be modified to attain uniform and complete surface coverage. The coating is composed of a mixture of anatase and rutile polymorphs doped with nitrogen (N), and it contains substoichiometric Ti and Ti species. Nitrogen doping results in a 0.4 eV band gap shift, while the defects induce photocurrent generation under visible light excitation up to 650 nm. Greater currents were observed in the nitrogen-doped titania at wavelengths above 450 nm vis-à-vis its (singularly) self-doped counterparts. The (photo)electrochemical behavior and photoactivity of the coating were evaluated by assessing redox species formation in a background aqueous solution. In the absence of any illumination, the coating behaved as an insulator and inhibited the activities of both oxidative and reductive species. On the other hand, under illumination, the coating enhances oxidation processes and inhibits reduction reactions within a near-field region wherein release of free radicals occurs and is constrained (delimited).