Photocatalyst of lamellar aggregates of RuOx-loaded perovskite nanosheets for overall water splitting

Overall photocatalytic splitting of water was achieved using a restacked aggregate of exfoliated nanosheets of Ca2Nb3O10, which was synthesized by flocculating a colloidal suspension of the nanosheets with alkali-metal ions and a trace amount of ruthenium red, a trinuclear complex of ([(NH3)(5)Ru-O-Ru(NH3)(4)-O- Ru(NH3)(5)]Cl-6. The as-restacked material showed the evolution of H-2 gas from water immediately after UV irradiation, while O-2 evolution was observed only after some induction time, which may be understood by the possible oxidation of ruthenium red to RuOx in the initial stage. The restacked aggregate, which was heated at 773 K to convert the ruthenium complex to the oxide, underwent the stoichiometric splitting of water upon initiation of UV illumination, verifying the hypothesis. Total decomposition of water could not be attained with the bulk layered host of KCa2Nb3O10 as well as its RuOx-loaded forms obtained via a conventional impregnation procedure. This clearly demonstrates the effectiveness of the present exfoliation-restacking route for loading RuOx to improve and enhance the photocatalytic activities of layered semiconducting materials. A homogeneous distribution of RuOx was suggested by XPS depth-profile analysis on the materials obtained through the exfoliation-restacking process.