Study on the effects of Cl and F doping in TiO2 powder synthesized by a sol-gel route for biomedical applications

Abstract

F- and Cl-doped (10 at%) TiO2 powders were prepared by a sol-gel route and calcined at different temperatures and for different times. X-ray diffraction, thermogravimetric- and differential-thermal analysis showed that doping suppressed both the amorphous to anatase transformation and the anatase to rutile transformation and refines the particle size. F was found to be more effective than Cl. Preliminary hemolysis and cytotoxicity testing demonstrated that F- and Cl-doped anatase powders were more hemolytic and toxic than the undoped anatase powder; however, the doped rutile powders were less hemolytic and toxic than the undoped rutile powder. The lattice strain (calculated from Rietveld analysis) was less for the doped rutile powders, which could explain their enhanced biocompatibility. X-ray photoelectron spectroscopy revealed the presence of Ti3+ in F-doped anatase powder. Ti3+ ions create reactive oxygen species and made the doped anatase sample less biocompatible. X-ray photoelectron spectroscopy revealed that when these doped samples were calcined at 400 °C or higher temperature, the doping ions disappeared from the material. Absence of the dopants may generate a significant defect per unit volume in anatase and influence the anatase to rutile nucleation density and particle size. Presumably, these higher-energy defects present in the doped powders acted as new nucleation sites, and higher temperature and/or a longer transformation time provided the ions with greater mobility to rearrange themselves. With a longer conversion time for the doped powders, the new rutile phase had less strain and greater thermodynamic stability.