Electronic, magnetic, optical properties, and morphological characteristics of nanocrystalline based on zinc–cobalt molybdate prepared by soft chemistry route

Abstract

We report on a simple technique for the preparation of nanocrystalline metal molybdate Zn1-xCoxMoO4 (0 ≤ x ≤ 1) using the polymeric route. The formation mechanism, homogeneity, and structure of the obtained powders were investigated with thermal analysis (TGA–DTA), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The morphology was examined by scanning electron microscopy (SEM), field emission scanning electron microscopy (SEM–FEG) and Brunauer–Emmett–Teller analysis (BET). The particle size was determined by transmission electron microscopy (TEM). UV–Visible spectroscopy and CIE L*a*b* colorimetric parameters were used for color characterization and measurement. According to the XRD analysis of the obtained compounds, for cobalt content greater than or equal to 45 %, the phase formed after grinding is isomorphic to α-CoMoO4. A triclinicphaseof zinc molybdate α-ZnMoO4 polycrystals compound is observed for the cobalt content less than or equal to 30 %. A triclinicstructure of α-ZnMoO4 and monoclinic symmetry of CoMoO4 coexist for cobalt contents between 30 % and 45 %. The solid solution Zn0.7Co0.3MoO4(ZnCoMo-0.3–600), which was obtained in an acidic environment, was formed of grains of quasi-spherical shape with nanometric sizes between 30 and 100 nm. The specific surface area (BET) of the nanocrystalline powders decrease as a function of the substitution of Co2+ in the ZnMoO4, the highest value recorded for the ZnCoMo-0.3–600 powder was about 56.7 m2g−1. As a result, we can claim clearly from the analysis of the diffuse reflection spectra that the thermochromism occurs from the shift of the O2–→Mo6+charge transfer band towards high energies. According to the optical band-gap energy (Eg = 2.153 eV), the monoclinic ZnCoMo-1–700 (CoMoO4) was classified as a semiconductor nanomaterial. The theoretical magnetic moment of this sample is approximately μtheorical = 5.00049 μB.