Nb2O5 nanoparticles obtained by microwave assisted combustion synthesis under different conditions

The microwave assisted combustion synthesis (MACS) as a new, quick and low cost synthesis method was used for preparation of niobium pentoxide (Nb2O5) powders. The present paper investigated the effect of reactant concentrations (ammonium niobium oxalate, urea and ammonium nitrate) on the characteristics of Nb2O5 nanoparticles. Three samples were synthesized with stoichiometric ratio between the fuel and oxidant (C1), excess of oxidant (C2) and excess of fuel (C3). In all samples, Nb2O5 crystalline nanoparticles with irregular morphology were detected. The synthesis of nanoparticles with smaller diameter in the C2 and C3 samples was confirmed by greater values of band gap energy measured through UV-Visible diffuse reflectance spectroscopy (indicating quantum confinement) and by the Rietveld refinement of X-ray diffraction patterns. The results showed that the amounts of oxidant and fuel can change synthesis temperature, influencing the final characteristics of the particles, such as size and existent phases. In these cases the excess of oxidant and fuel in the C2 and C3 samples, respectively, decreases the average synthesis temperature and decelerates the particle growth and the formation of the monoclinic phase.