Novel Synthesis of Spinel Mn x Co1−x Al2 O 4 (x = 0.0 to 1.0) Nanocatalysts: Effect of Mn2+ Doping on Structural, Morphological, and Opto-Magnetic Properties

Abstract

In this present study, Mn2+doped CoAl2O4 (MnxCo1−xAl2O4; x = 0.0 to 1.0) spinel nanoparticles were synthesized by microwave combustion method using nitrates of Co, Mn, and Al as the starting materials and urea was used as the fuel. The effects of Mn2+ doping on structural, morphological, opto-magnetic and catalytic properties were studied. Powder X-ray diffraction analysis was confirmed the formation of cubic spinel aluminate structure. Debye-Scherrer’s formula was used to estimate the average crystallite size of the samples and was found to be in the range of 18.26 to 21.47 nm. It was observed that the calculated lattice parameter value is increased from 8.215 to 8.247 A with increasing the Mn2+ content due to the higher ionic radius of Mn2+ ion. High resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analysis confirmed the nano-sized particle-like morphology of the samples. Energy dispersive X-ray (EDX) results showed the pure form of spinel aluminate structure. The band gap energy (Eg) of undoped CoAl2O4 was estimated to be 3.58 eV from UV-visible diffuse reflectance spectroscopy (DRS), and the Eg values increased with increase of Mn2+ ions due to the decrease of grain size. The magnetic hysteresis (M-H) loop showed the superparamagnetic nature of the samples, and the saturation magnetization values increased with increasing Mn2+ ions, which was confirmed by vibrating sample magnetometer (VSM). All compositions of the samples were successfully tested as catalyst for the conversion of benzyl alcohol into benzaldehyde and observed good catalytic activity.