Restacked perovskite nanosheets and their Pt-loaded materials as photocatalysts

Colloidal perovskite nanosheets of [Ca2Nb3O10](-) were reassembled by flocculation with aqueous solutions containing alkali metal ions. X-ray diffraction and chemical analysis data on the derived products indicated that a limited number of nanosheets were restacked in such a way as to restore a layered structure that accommodated alkali metal ions and water molecules between the nanosheets. This exfoliation/restacking process resulted in porous aggregates of fine crystallites with high specific surface areas compared to those of the original layered perovskite. The aggregates showed high photocatalytic activity for hydrogen gas generation from an aqueous methanol solution. A maximum evolution rate of 550 mumol h(-1) was achieved at an optimum loading of Pt, which is higher than KCa2Nb3O10 (63 mumol h(-1)) and P-25 titanium oxide (390 mumol h(-1)). Photoirradiation of a colloidal nanosheet suspension containing H2PtCl6 allowed direct deposition of Pt nanoparticles on the surfaces of single-layer nanosheets. Pt single crystals as small as 1 nm were loaded onto nanosheets when Pt loading was 0.1 wt %, while larger polycrystalline particles of up to 10 nm were deposited when Pt loading was 3 wt %. The Pt-loaded nanosheets were flocculated with alkali metal ions, and the resulting aggregates showed a maximum activity of 900 mumol h(-1) for hydrogen generation when Pt loading was 0.1 wt %.