Factors controlling pure-phase magnetic BiFeO3 powders synthesized by solution combustion synthesis

Bismuth ferric oxide nanopowders were prepared through combustion method. Pure phase and well-crystallized BiFeO3 can be obtained by controlling the combustion process, fuel type and fuel-to-oxidant ratio. The evolutions of phase constitution and structural characteristics of the as-resulted nanopowders were investigated by X-ray diffraction, scanning electron microscope, and simultaneous thermogravimetric analysis. The results revealed that both the type and amount of fuel have to be carefully considered because they play an important role in total reaction characteristics. Among all tested fuels, l-α-alanine and glycine are the suitable fuels for BiFeO3 synthesis. For α-alanine, the optimal fuel-to-oxidant ratio is 0.22, which results in a suitable flame temperature for BiFeO3 formation. Still, too little fuel would result in only amorphous phase powders due to the low flame temperature and too much fuel would lead to transformation of the BiFeO3 phase to impurities because of the high flame temperature involved. The resulting BiFeO3 nanopowders exhibited strong H2O2-activiting ability and weak magnetism. When BiFeO3 nanopowders were used as a heterogeneous Fenton-like catalyst to degrade rhodamine B (RhB), the apparent rate constant for RhB degradation in the presence of H2O2 at pH 5.0 was evaluated to be 0.048 min−1.

► Both the type and amount of fuel strongly affect the phase composition and crystallinity of the as-synthesized product.
► The system needs a careful optimisation of these parameters to obtain pure-phase and well-crystallized BiFeO3 nanopowders. An optimization of these parameters could improve the quality of the final products.
► Among all tested fuels, l-α-alanine and glycine are the suitable fuel for BiFeO3 synthesis. The optimal fuel-to-oxidant ratio (F/NO3−) of α-alanine and glycine for pure-phase BiFeO3 synthesis is 0.22 (fuel-lean reaction, −33%) and 0.37 (fuel-lean reaction, −34%), respectively, which results in a suitable flame temperature that favors the formation of BiFeO3 phase.
► Still, too little fuel would result in only amorphous phase powders due to the low flame temperature and too much fuel would lead to transformation of the BiFeO3 phase to impurities (Bi2Fe4O9 and Bi25FeO39 phases) because of the high flame temperature involved.
► The resulting BiFeO3 nanopowders exhibited strong H2O2-activiting ability and weak magnetism. When BiFeO3 nanopowders were used as a heterogeneous Fenton-like catalyst to degrade rhodamine B (RhB), the apparent rate constant for RhB degradation in the presence of H2O2 at pH 5.0 was evaluated to be 0.048 min−1.