Cu2O-sensitized TiO2 nanorods with nanocavities for highly efficient photocatalytic hydrogen production under solar irradiation

•Development of simple method to generate nanocavities on TiO2 nanorods.•Influence of calcination temperature on size, shape, depth and density of nanocavities.•Nanocavities on TiO2 nanorods exhibit interesting optical and catalytic properties.•Experimental conditions are optimized to get high rate of H2 production.•The sensitizer, Cu2O in Cu2O/TiO2 nanocomposite is stable after 5 cycles.

Hydrogen trititanate (H2Ti3O7) nanorods were synthesized by using a hydrothermal method. The transformation of the crystal structure from H2Ti3O7 to TiO2 occurred into either single crystalline TiO2 (B) [calcined at 400 or 450 °C] or bicrystalline TiO2 (B) with anatase phases [calcined at 500 or 550 °C] during a calcination process. Calcination temperature from 450 to 550 °C induced both phase transformation and formation of large size nanocavities, and the changes in the nanorods morphology were confirmed using HRTEM/TEM images. Nanocomposites of Cu2O/TiO2 nanorods with different copper loading (CuxTNR) were prepared by using the wet impregnation method with TiO2 nanorods [calcined at 500 °C] and copper nitrate as copper source. The structural, optical, surface elemental and morphological properties of the synthesized catalysts were extensively characterized. Solar photocatalytic hydrogen (H2) production experiment was carried out with aqueous-glycerol solution for 4 h. The photocatalytic activity of TiO2 nanorods that are calcined at 500 °C exhibited very high rate of H2 production, is ascribed to the improved separation of electron/hole pairs and catalytic activity at bicrystalline TiO2 surface. For the first-time, we have achieved the higher rate of H2 (50,339 µmol h−1 g−1cat) production under the set of the optimized conditions using Cu1.5TNR nanorods containing nanocavities as catalyst under solar irradiation. This enhancement in the activity can be attributed to the desirable absorption of UV–visible light in natural solar spectrum and minimization of the recombination of electron–hole pairs, multiple internal reflection of light within nanocavities, which improved the surface–interface reactions. The present study clearly demonstrated that Cu loaded on titania nanorods containing nanocavities were found to be more efficient and promising photocatalyst for H2 production under solar light irradiation.

Graphical abstractA unique combination of Cu2O dispersed in nanocavities of TiO2 nanorods facilitates high catalytic hydrogen production at the rate of 1205 and 50,332 µmol h−1 g−1cat in water and aqueous glycerol. The observed higher rate of H2 prouction due to visible light sensitization of Cu2O, enhanced UV-A absorption, one dimentional nanorod structure, multiple internal reflection,bicrystalline strucutre of TiO2 etc., which retard the charge carriers recombination and further enhance better surface–interface reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide