One-step CoFe₂O₄ gel combustion synthesis using tris(hydroxymethyl) aminomethane (TRIS) as alternative fuel: Control of oxidiser-to-fuel molar ratio for tuning its structural, magnetic, and optical properties br

Spinel ferrites are promising candidates for various applications as transformers, transducers, inductors in the electronic field, sensors, biosensors and hyperthermia agents in the biomedical field. Combustion synthesis, as a method for obtaining ferrites, is gaining attention. However, most fuels generate high ignition temperatures, which lead to larger (micrometric) crystallites or even render combustion synthesis unfeasible in a single step. Spinel cobalt ferrite (CoFe2O4) has unique features that facilitate tuning the spinel structure based on modifications in the synthesis parameters. In this study, CoFe2O4 was synthesised via gel combustion using tris (hydroxymethyl)aminomethane (tris) as an alternative fuel. The effect of the oxidizer-to-fuel molar ratio (psi) on their formation and structural, optical, and magnetic properties were evaluated. Gels were prepared from metal nitrates and tris at psi values of 0.6, 0.8, 1.0, 1.2, and 1.4. Thermal analysis of the ignition temperature was found to be dependent on psi. The adiabatic flame temperatures were estimated using thermodynamic calculations, as 2688.36 K when psi = 0.6, and 1017.56 K when psi = 1.4, which indicates that the temperatures would be sufficient to form the phase in one step without additional thermal treatment. X-ray diffraction confirmed the formation of CoFe2O4 as a single-phase for all psi values. Raman and Fourier transform infrared spectroscopy confirmed the formation of CoFe2O4 for all psi values investigated. The low bandgap values (0.92-1.36 eV) suggest several promising applications in photoactivated materials. The magnetic properties of the as-prepared powders measured by a vibrating sample magnetometer revealed saturation magnetisation values, Ms, and coercivity field, Hc, and remanence magnetisation were dependant on psi. These results show that tris can be used as a fuel to synthesise spinel ferrites via one-step gel combustion with excellent properties for several applications.