Synthesis and Characterization of La (Ti,Nb)(O,N)3 for Photocatalytic Water Oxidation

Perovskite-type La(Ti,Nb)(O,N)3 powders with different Ti and Nb content were synthesized by a thermal ammonolysis of oxide precursors prepared via a soft chemistry route. By X-ray diffraction (XRD), a gradual increase of the unit cell volume was observed with increasing niobium content. The crystallite size calculated with the Scherrer equation displayed a minimum of about 30 nm at the intermediate composition. Scanning electron microscopy (SEM) showed morphological changes of the microstructure with increasing niobium content. Thermal re-oxidation studies with thermogravimetric analysis (TGA) revealed that a different amount of nitrogen was substituted into the La (Ti,Nb)(O,N)3 lattice. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) showed that absorption edge wavelengths of the oxynitrides were in the range of 612 nm – 744 nm, corresponding to the bandgap energy of 2.02 eV – 1.67 eV. Among all La(Ti,Nb)(O,N)3, LaTiO2N showed the highest photocatalytic activity for water oxidation. One of the determining factors for the photocatalytic water oxidation with La(Ti,Nb)(O,N)3 was found to be the defects concentration.