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 H₂ 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