Visible-light-induced photocatalytic activity in FeNbO₄ nanoparticles

A novel method was used to synthesize orthorhombic FeNbO₄ nanoparticles by a hydrothermal process followed by calcination at 600°C, and their optical, photoelectrochemical, and photocatalytic properties were investigated. The microstructural and local structural properties were characterized using X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM), and Raman spectroscopy. The FeNbO₄ particles obtained were composed of much smaller nanocrystallines, with an average size of 10-20 nm, compared to particles prepared at 1000°C through a conventional solid-state reaction method. Moreover, the optical band gap energy of the nanoparticles was estimated to be 1.93 eV from the UV-vis diffuse reflectance, and their flat-band potential in 1 M NaOH was -0.4 V (SCE). The X-ray photoelectron spectroscopy analysis revealed that the nanoparticles had fewer surface defects, such as oxygen vacancies, than the particles prepared by the solid-state reaction method. The FeNbO ₄ nanoparticles also exhibited a much higher photocatalytic activity for the degradation of rhodamine B dye solution under visible light irradiation (>420 nm). This higher photocatalytic activity of the FeNbO₄ nanoparticles was attributed to their higher optical absorption ability and smaller particle size, as well as fewer surface defects.