Band alignment investigations of heterostructure NiO/TiO2 nanomaterials used as efficient heterojunction earth-abundant metal oxide photocatalysts for hydrogen production

Earth-abundant NiO/anatase TiO2 heteronanostructures were prepared by a straightforward one-pot solgel synthetic route followed by a suitable thermal post-treatment. The resulting 0.1-4 wt% NiO-decorated anatase TiO2 nanoparticles were characterized by X-ray diffraction, electron microscopy, Raman and UV-visible spectroscopy and N-2 sorption analysis, and showed both nanocrystallinity and mesoporosity. The careful determination of the energy band alignment diagram by a suitable combination of XPS/UPS and absorption spectroscopy data revealed significant band bending at the interface of the p-n NiO/ anatase TiO2 heterojunction nanoparticles. Furthermore, these heterojunction photocatalysts exhibited an improved photocatalytic activity in H-2 production by methanol photoreforming compared to pure anatase TiO2 and commercial P-25. Thus, an average H-2 production rate of 2693 mmol h(-1) g(-1) was obtained for the heterojunction of a 1 wt% NiO/anatase photocatalyst, which is one of the most efficient NiO/anatase TiO2 systems ever reported. An enhanced dissociation efficiency of the photogenerated electron-hole pairs resulting from an internal electric field developed at the interface of the NiO/anatase TiO2 p-n heterojunctions is suggested to be the reason of this enhanced photocatalytic activity.