Study of Photo-absorption and Photoelectrolytic Properties of Novel Photocatalysts

Large surface area nanotubes have been considered to be an effective structure for sufficient active point promotion for photocatalyst. In this research, anodization of Ti foils was utilized for ordered arrays of TiO2 nanotubes photocatalyst fabrication. High temperature annealing (600°C to 750°C) under reduction (99%N2/1%H2) and ambient atmosphere was applied for oxygen vacancies generation for which the photocatalytic reaction to occured. Progressing blue-shift was appeared in UV-Vis spectra which revealed the band gap evolution under different annealing temperature, moreover, gradually rise in optical density at visible region (from 400 nm to 800 nm) was observed in the cases of 600℃ to 750℃ annealed samples. X-ray diffraction (XRD) analysis results demonstrated phase transition of TiO2 nanotubes from anatase to rutile with respected to different annealing temperature, decreasing in intensity of diffraction peaks about Ti foil was also observed. Oxygen concentration was found to increase with depth by XPS depth profile observation. To the above regards, oxygen vacancies were proposed to be generated during annealing treatment by phase transition caused lattice mismatch and oxygen atoms diffusion, especially in high temperature annealed cases.
To the aspect of photocatalystic activity, greatest current density with respect to given potential was found to be 1 V for TiO2 nanotubes annealed under both reduction and ambient atmospheres for 4 hrs at 600℃, and the photon-to-hydrogen generation efficiency monitored at this potential was in the range of 1.8~2.1%.
To extend the working wavelength of photocatlayst to visible region, (Ag0.75Sr0.25)(Nb0.75Ti0.25)O3 photocatalyst was fabricated by Ag2O, Nb2O5, SrCO3 and TiO2 mixed powders. Surfactant (Darvan C) was conditionally used to facilitate the powder mixture before sintered. For comparison, photocatalyst composed by Ag2O, Nb2O5 and SrTiO3 was also preformed. According to XRD testing results, AgNbO3 was found to be the dominant phase in both cases. UV/Vis spectra demonstrated (Ag0.75Sr0.25)(Nb0.75Ti0.25)O3 photocatalyst fabricated by three and four powders mixture with surfactant got higher optical intensity in absorption for which would further enhance photocatalytic performance in visible region.