Effect of pH and surfactant on band gap properties of monoclinic FeNbO₄ prepared via different routes

A novel approach was used to synthesize monoclinic FeNbO₄ nanoparticles by three distinctive routes process followed by calcination at 1100 °C for 6h. Optical properties were investigated by calculating band gap shift of prepared nanoparticles using diffuse reflectance spectroscopy (DRS). Band gap measurements of prepared samples were found to be in the range 1.81–2.25 eV indicating that all prepared nanoparticles exhibit visible light absorption. FeNbO₄ prepared using co-precipitation method at pH =7 showed the lowest band gap energy of 1.81 eV. A red shift was observed for FeNbO₄ prepared under pH =2 using co-precipitation method. On the other hand, when surfactant assisted co-precipitation approach is used a 40 nm blue shift is observed. Moreover, all nanoparticles were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Brunauer–Emmett–Teller (BET) for determination of the specific surface area and porosity. The crystallite size was calculated using Scherrer's equation and found to be in the range 40.77–49.06 nm.