Titanium Doping and Its Effect on the Morphology of Three Dimensional Hierarchical Nb3O7(OH) Nanostructures for Enhanced Light-Induced Water Splitting

This study presents a simple method that allows us to modify the composition, morphological, and surface properties of three-dimensional hierarchical Nb3O7(OH) superstructures, resulting in strongly enhanced photocatalytic H-2 production. The superstructures consist of highly ordered nanowire networks and self-assemble under hydrothermal conditions. The presence of titanium affects the morphology of the superstructures, resulting in increased surface areas for higher doping levels. Up to 12 at. % titanium is incorporated into the Nb3O7(OH) crystal lattice via substitution of niobium at its octahedral lattice sites. Further titanium excess results in the formation of niobium-doped TiO2 plates, which overgrow the surface of the Nb3O7(OH) superstructures. Photoluminescence spectroscopy indicates fewer charge recombination processes near the surface of the nanostructures with an increasing titanium concentration in the crystal lattice. The combination of larger surface areas with fewer quenching sites at the crystal surface yields higher H2 evolution rates for the doped samples, with the rate being doubled by incorporation of 5.5 +/- 0.7 at. % Ti.