A Novel Synthesis of Zn2+-Doped CoFe2O4 Spinel Nanoparticles: Structural, Morphological, Opto-magnetic and Catalytic Properties

Zn2+-doped CoFe2O4 (ZnxCo1-xFe2O4: where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) spinel nanoparticles (NPs) were synthesized by microwave combustion method using nitrates of cobalt, zinc, and iron as the starting materials and urea used as the fuel. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), energy dispersive X-ray (EDX), and selected area electron diffraction (SAED) pattern analyses showed that all composition was found to have pure cubic spinel structure with well crystalline nature. The average crystallite size of the samples was found to be in the range of 25.43 and 29.46 nm. The lattice parameter increased from 8.432 to 8.441 angstrom with increasing the Zn2+ content, due to the smaller ionic radius of Co2+ substituted by larger ionic radius of Zn2+, which was determined by Rietveld analysis. High-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analyses were used to study the morphological variation, and the results showed a nano-sized spherical-shaped particle-like morphology. The band gap (E-g) of the undoped CoFe2O4 was estimated to be 2.69 eV from UV-Vis diffuse reflectance spectroscopy (DRS). With the increase of Zn2+ dopant, the E-g value decreased from 2.61 to 2.01 eV, due to the difference of particle size of the samples. The magnetic hysteresis (M - H) loop confirmed the ferromagnetic nature of undoped CoFe2O4 with magnetization (M-s) of 64.85 emu/g, and it is decreased with increasing the Zn2+ content in CoFe2O4 spinel, which was confirmed by a vibrating sample magnetometer (VSM). All composition of spinel ZnxCo1-xFe2O4 samples were successfully tested as catalyst for the conversion of benzyl alcohol, which has resulted 91.73 and 95.82 % conversion efficiency of CoFe2O4 and Zn0.4Co0.6Fe2O4 nano-catalysts, respectively.