Solid-State ¹³C NMR Characterization of Carbon-Modified TiO₂

13 C-modified TiO 2 was prepared to facilitate study of the dopant atoms and trace their chemical fate throughout the process. In the preannealed material, NMR showed strong evidence of many Ti−O−C bonds. After annealing, surface-bound coke is a major component. NMR also showed that a washing step before annealing led to the generation of orthocarbonate (C(OR) 4 ) centers, observed at 126 ppm, which are located deep inside the TiO 2 particles. Both NMR and XPS confirmed the presence of small amounts of regular sp 2 -hybridized carbonate species in all briefly annealed samples, while annealing for longer times led to a reduction removal of the CO n centers. Quantitative NMR also shows the degree of carbon loss that accompanies annealing. Some variation in the chemical degradation of quinoline is noted among the catalysts, but coke-containing TiO 2 catalysts are not qualitatively better catalysts for use with visible light with this substrate.