Calcium niobate semiconductor nanosheets as catalysts for photochemical hydrogen evolution from water

We have studied the photochemical water splitting activity of individually dispersed, semiconductor nanosheets derived from the Dion-Jacobsen phase HCa2Nb3O10 by exfoliation with tetrabutylammonium hydroxide. The dimensions of the nanosheets are 0.001 x 1.2 x 1.2 mu m(3) based on TEM measurements and crystallographic data, and their band gap is determined as 3.53 eV based on the absorption band edge at 350 rim. When an aqueous suspension of the nanosheets is irradiated with light from a Hg lamp, hydrogen is produced at rates of up to 2.28 mu mol/h with a quantum efficiency (QE) of 0.22%. No oxygen is evolved. Derivatization of the nanosheets with Pt nanoparticles increases the hydrogen production rate to 78.37 mu mol (QE = 7.5%). Restacking of the nanosheets at low pH does not significantly affect the catalytic activity. Transient absorption measurements of the nanosheets reveal charge separation on a nanosecond time scale.