Yanping Sun

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

Carbon-doped TiO(2) have received attention recently because of their potential for environmental photocatalysis and solar hydrogen conversion applications. Three different carbon-doped TiO(2) nanoparticle materials were synthesized via sol-gel and hydrothermal procedures, and analyzed by (13)C 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. (13)C SSNMR analyses of TiO(2-)(x)C(x) displayed signals corresponding to carbonate-type or sp(2)-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 TiO(2-)(x)C(x) 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.

Photoelectrochemical and structural characterization of carbon-doped In2O3 and carbon-doped WO3 films prepared via spray pyrolysis

Carbon-doped In2O3 and carbon-doped WO3 films were produced using a spray pyrolysis methodology with octanoic acid as the carbon dopant source. C-doped and undoped In2O3 films showed a cubic polycrystalline In2O3 structure, and C-doped and undoped WO3 films displayed a monoclinic polycrystalline WO3 structure. C-doped In2O3 and WO3, compared to their corresponding undoped materials, showed increased absorption in the 350-550 nm range with a red shift in the band gap transition. The presence of carbonate-type species in these C-doped samples was confirmed by XPS. The photoelectrochemical activity was evaluated under near UV-visible light and visible light only irradiation conditions. Under the same irradiation conditions, C-doped In2O3 and C-doped WO3 electrodes produced greater photocurrent densities than their corresponding undoped electrodes. The C-doped In2O3 electrode exhibited photocurrent densities up to 1 mA/cm2, with 40% from visible light irradiation, and the C-doped WO3 electrode showed photocurrent densities up to 1.3 mA/cm2, with 50% from visible light irradiation. These results indicate the potential for further development of In2O3 and WO3 photocatalysts by simple wet chemical methods, and provide useful information towards understanding the structure and enhanced photoelectrochemical properties of these materials.