Solid-state NMR and EPR analysis of carbon-doped titanium dioxide photocatalysts (TiO2−xCx)

Carbon-doped TiO2 have received attention recently because of their potential for environmental photocatalysis and solar hydrogen conversion applications. Three different carbon-doped TiO2 nanoparticle materials were synthesized via sol-gel and hydrothermal procedures, and analyzed by 13C solid-state nuclear magnetic resonance (SSNMR) and other methods to characterize the environment of the doping species. UV/vis spectra and powder X-ray diffraction (XRD) patterns showed that the synthesized materials absorbed visible light and their crystal structures corresponded to anatase. 13C SSNMR analyses of TiO2−xCx displayed signals corresponding to carbonate-type or sp2-type carbon species. Variable contact CP-MAS and dipolar dephasing analyses gave evidence for the presence and proximity of H atoms near these carbonate species. Electron paramagnetic resonance (EPR) spectroscopy showed that the thermally oxidized TiO2−xCx displayed a complex mixture of point defects, electron and hole trapping centers, all attributable to the incorporation of carbon, while the XPS data ruled out the presence of carbide species.