A Novel Synthesis, Structural, Morphological, and Opto-magnetic Characterizations of Magnetically Separable Spinel CoxMn1-xFe2O4 ( 0 ≤ x ≤ 1) Nano-catalysts

Spinel CoxMn1-xFe2O4 (0 <= x <= 1) nanocrystals were successfully synthesized by a simple microwave-assisted combustion method. High-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analysis was used to study the morphological variations and found the particlelike nanocrystal morphologies. Energy dispersive X-ray (EDX) results showed that the composition of the elements were relevant as expected from the combustion synthesis. Powder X-ray diffraction (XRD) analysis showed that all composition was found to have cubic spinel-type structure. Average crystallite size of the samples was found to be in the range of 10.36-21.16 nm. The lattice parameter decreased from 8.478 to 8.432 angstrom with increasing Co2+ content. Fourier transform infrared (FT-IR) spectra showed two strong absorption peaks observed at lower frequency (similar to 435 to similar to 800 cm(-1)), which can be assigned to the MO (Mn, Co, and Fe) bonds. UV-Visible diffuse reflectance spectroscopy (DRS) shows that the energy band gap of pure MnFe2O4 is 1.78 eV and with increase in the Co2+ ion, it increases from 1.87 to 2.33 eV. Addition of Co2+ in MnFe2O4 reduces the particle size, which can be confirmed by the blue shift in the photoluminescence (PL) spectra. Vibrating sample magnetometer (VSM) results that confirmed a weak ferromagnetic behavior for all composition with saturation magnetization values in the range of 50.05 +/- 04 to 67.09 +/- 03 emu/g. All composition of spinel CoxMn1-xFe2O4 nano-crystals were successfully tested as catalyst for the oxidation of benzyl alcohol to benzaldehyde, which has resulted 87.32 and 94.28 % conversion efficiency of MnFe2O4 and Co0.6MnFe2O4, respectively.