Band Gap Narrowing of Orthorhombic Sodium Tantalate by Iron Doping and Photocatalytic Hydrogen Evolution by Water Splitting

In this work we have narrowed the band gap of orthorhombic sodium tantalate by doping the perovskite structure with 5 and 10% of iron. The hydrothermal method was used in the preparation of the samples. Moreover, the evolution of hydrogen by photocatalytic water splitting is reported for first time for orthorhombic NaTaO₃ mono-doped with Fe. The band gap was reduced from 4.08 to 3.24 eV for sodium tantalate doped with 5% of Fe, and up to 2.05 eV for the perovskite doped with 10% of Fe. The highest photocatalytic activity was obtained with the semiconductor that had 5% of Fe. Which was attributable to its smaller particle size, larger specific surface area and lower recombination of electron–hole pairs in contrast with the sample that had 10% of Fe. X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, nitrogen physisorption, ultraviolet–visible diffuse reflectance and photoluminescence spectroscopies were used to analyze the perovskite materials.