The sustainable and eco friendly green synthesis report on the use of plant extract alternate to chemicals has been discussed. In this work, opuntia plant extract is used as a natural reagent to synthesize nanoparticles. Herein, we demonstrate two methods namely, conventional and microwave method for the synthesis of nanoparticles using plant extract, due to its easy handling and bio-compatibility. Both the methods were carried out under the same conditions to explore the comparison of the data. Various characterization techniques were used to determine the crystallinity, crystallite size, lattice parameter, morphology, elemental composition, band gap energy, emission, saturation magnetization, and coercivity of the as-synthesized nanoparticles. A brief discussion about the importance of using the plant extract as well as the importance of microwave heating were discussed and summarized. The phase identification was examined using XRD analysis, which showed the formation of single and pure phase without any post annealing in microwave heating method. The formation of pure phase ferrites is also confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The surface morphology of ZnFe2O4 nanoparticles showed spherical shape and the size difference depends upon the method of synthesis. EDX analysis confirms the phase-purity of the as-synthesized nanoparticles. UV–Vis DRS of the as-obtained nanospheres exhibited the absorbance in the visible region. VSM analysis showed that the sample prepared by microwave technique exhibited better magnetic behaviour at room temperature than that of the ones prepared by the conventional heating method. The microwave heating technique produces nano-ferrites with high yield, low crystallite size, uniform morphology, and good absorption properties than the conventional heating method. Zinc ferrites were used in the catalytic reaction for the oxidation of glycerol into formic acid. The catalyst exhibit good catalytic performance and better selectivity of formic acid throughout the reaction. The plausible mechanism has been proposed. © 2017 Elsevier B.V.