Magnetic and electrochemical behaviour of cobalt doped tungsten oxide (WO3) nanomaterials by microwave irradiation method

Abstract

Nanocrystalline WO3·H2O nanopowders, doped with cobalt (2 and 5 wt%) have been synthesized using CoCl2·6H2O and Na2WO4·2H2O in a facile microwave irradiation process, followed by the annealing process. The samples were characterized with powder X-ray diffraction, field emission scanning electron microscopy, UV-VIS diffusion reflectance spectroscopy, photoluminescence spectroscopy and cyclic voltammetry (CV). X-ray diffraction patterns showed both undoped and Co doped WO3·H2O crystallized with orthorhombic phase. Annealing h-WO3 at 600 °C 6 h in air resulted in the different products, W17O47 (monoclinic) for undoped, WO3 orthorhombic for 2 wt% Co doped and WO3 (monoclinic) for 5 wt% Co doped. FE-SEM micrographs suggested that the dopants are able to influence the growth rate and morphology of the prepared nanopowders. UV-VIS-DRS spectra revealed that the dopant (Co ion) is incorporated in the intermediate energy level. Blue emissions (450–550 nm) were verified using PL at room temperature for the annealed samples (W17O47 and WO3) with excitation wavelength 390 nm. The difference in peak intensity observed through PL spectra attributed to the possible distortions in WO42− tetrahedron group during microwave irradiation process. Electrochemical studies showed the possible enhanced catalytic behaviour of cobalt doped (5 wt%) as prepared samples than that of others. The temperature dependent magnetic susceptibility (300 K–2 K) and isothermal magnetization measurements showed the enhancement in magnetic behaviour of the samples for diamagnetic to antiferromagnetic nature which is clearly shows the incorporation of Cobalt ion at tungsten lattice site and in determining the resultant magnetic behaviour of the samples.