K4Nb6O17-derived photocatalysts for hydrogen evolution from water: Nanoscrolls versus nanosheets

The layered hexaniobate K4Nb6O17 is known as a photocatalyst for methanol dehydrogenation and hydrogen evolution from water under ultraviolet (UV) light. Here we show that the activity is retained in propylammonium- (PA) or tetrabutylammonium- (TBA) stabilized H2K2Nb6O17 nanosheets and TBA-stabilized H4Nb6O17 nanoscrolls that can be obtained by exfoliation of K4Nb6O17 followed by cation exchange. The catalytic activity of the exfoliated systems is comparable to K4Nb6O17, with scrolls being most active in water, and PA sheets giving enhanced H2 rates due to sacrificial electron donor action of PA. Femtosecond absorption spectra for TBA scrolls and PA sheets exhibit broad features between 450 and 700 nm due to trapped holes and electrons. Electron–hole recombination follows approximately second-order kinetics, with rates of decay similar for sheets and scrolls. In addition, catalysts were characterized with UV/vis and fluorescence spectroscopy and transmission electron microscopy.