Abstract:

In this study, for the first time, caffeine and citrulline were used as fuels for the synthesis of the spinel ferrite CoFe2O4 by gel combustion. The influence of the oxidizer to fuel molar ratio (φ) on the synthesis of cobalt ferrite was studied. X-Ray Diffraction (XRD) showed that the spinel phase was obtained in all the combustions, but the use of caffeine as fuel allowed it to be obtained with high purity, while in the other combustions CoO appeared as a secondary phase due to changes in the reaction. Furthermore, the crystallite size was estimated using the Scherrer equation and considering the plane (311), finding it to be in the range of 32–40 nm, and increasing as the amount of fuel was increased. In addition, the adiabatic flame temperatures were estimated, finding that, in the synthesis with φ = 0.7, the flame temperatures were 1974 K and 1711 K, for the caffeine and citrulline respectively, which could be sufficient to obtain the phase in one stage. The ignition temperatures identified by DSC/TG thermal analysis for caffeine and citrulline samples with φ = 1.0 were 297 and 191 °C, respectively, which are in the range of traditional fuels. The morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which revealed that the particles were agglomerated as a result of high reaction temperatures. The magnetic properties identified by the vibrating sample magnetometer (VSM) for the sample with caffeine and ratio φ = 0.7 were saturation magnetization Ms = 95.16 emu g−1, coercivity field Hc = 710.76 Oe and remanent magnetization Mr = 44.86 emu g−1. Meanwhile, with citrulline and ratio φ = 0.7, the properties were saturation magnetization Ms = 59.14 emu g−1, coercivity field Hc 837.15 Oe and remanent magnetization Mr = 32.30 emu g−1. It should be pointed out that the high saturation magnetization values obtained with caffeine fuel exceed those reported with traditional fuels. The obtained results allow us to infer that these fuels could be used as alternatives in synthesizing inorganic oxides by combustion in one step.

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