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.
Microwave-Assisted Auto-Combustion Synthesis of Binary/Ternary CoxNi1−xFerrite for Electrochemical Hydrogen and Oxygen Evolution