Solar light sensitized p-Ag2On-TiO2 nanotubes heterojunction photocatalysts for enhanced hydrogen production in aqueous-glycerol solution

Solar light harvesting nano-heterojunction p-Ag2O/n-TiO2 nanotube catalysts were successfully synthesized by a combination of hydrothermal and wet impregnation methods. The crystal structure and surface morphology analysis revealed that n-TiO2 composed of biphasic anatase-rutile with nano-tubular morphology. The X-ray photoelectron spectrum confirmed the presence of Ti4+ and Ag+ in the form of TiO2 and Ag2O, the results are in good agreement with TEM images. Moreover, DRS UV-Vis spectra and photocurrent density measurements indicated that Ag2O/TiO2 nanotubes have shown strong absorption in visible region and improved current production that indicates the hetero-junction properties. The Ag2O loaded (0.5-2.0 wt%) TiO2 nanotubes showed 26 folds enhanced photocatalytic hydrogen (H-2) production in glycerol/water mixture than the standard TiO2 P-25 under solar light irradiation. Interestingly, the catalytic recyclability tests carried out in pure water and glycerol/water mixture exhibited similar rate of H-2 production without significant loss in catalytic activity. Furthermore, the photocatalytic activity conducted in summer season exhibited higher rate of H-2 production than the experiments conducted during winter season owing to the variation in solar flux. The high rate of H-2 production can be attributed to the synergistic functions of 1-D nano-tubular morphology, hetero-junction formed between biphasic TiO2 photocatalyst and visible light active Ag2O as sensitizer. Based on the experimental results, a possible electron-hole transfer mechanism was also proposed. (C) 2016 Elsevier B.V. All rights reserved.