Paramagnetism of cobalt-doped ZnO nanoparticles obtained by microwave solvothermal synthesis

Abstract

Zinc oxide nanopowders doped with 1-15 mol % cobalt were produced by the microwave solvothermal synthesis (MSS) technique. The obtained nanoparticles were annealed at 800 °C in nitrogen (99.999%) and in synthetic air. The material nanostructure was investigated by means of the following techniques: X-ray diffraction (XRD), helium pycnometry density, specific surface area (SSA), inductively coupled plasma optical emission spectrometry (ICP-OES), extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and with magnetometry using superconducting quantum interference device (SQUID). Irrespective of the Co content, nanoparticles in their initial state present a similar morphology. They are composed of loosely agglomerated spherical particles with wurtzite-type crystal structure with crystallites of a mean size of 30 nm. Annealing to temperatures of up to 800 °C induced the growth of crystallites up to a maximum of 2 μm in diameter. For samples annealed in high purity nitrogen, the precipitation of metallic α-Co was detected for a Co content of 5 mol % or more. For samples annealed in synthetic air, no change of phase structure was detected, except for precipitation of Co 3 O 4 for a Co content of 15 mol %. The results of the magentometry investigation indicated that all as-synthesized samples displayed paramagnetic properties with a contribution of anti-ferromagnetic coupling of Co-Co pairs. After annealing in synthetic air, the samples remained paramagnetic and samples annealed under nitrogen flow showed a magnetic response under the influences of a magnetic field, likely related to the precipitation of metallic Co in nanoparticles.

Cytotoxic effects of ZnO nanoparticles on mouse testicular cells

“…These characteristics are consistent with those of ZnO NPs prepared by solvothermal processes and indicate that the produced ZnO NPs possess a narrow size distribution and quasispherical to hexagonal shapes which are suitable for further toxicity studies. 31 Particle size distribution was performed by DLS, which showed the average size as between 20 and 110 nm ( Figure 1D). …”

Significance of polymethylmethacrylate (PMMA) modification by zinc oxide nanoparticles for fungal biofilm formation

“…The complete method of preparation and characteristics of ZnO-NPs used in this study were described in a previously published articles (Cierech et al, 2016, Wojnarowicz et al, 2015. Nevertheless the main features are presented below.…”

Selective Oxidation of Styrene to Benzaldehyde by Co‐Ag Codoped ZnO Catalyst and H2O2 as Oxidant

“…On the other hand, the peaks associated with the cobalt oxide or cobalt hydroxide phases such as CoO or Co(OH) 2 were not detected as shown in the XRD patterns ( Figure 2). According to Wojnarowicz et al [15], some precipitation of Co 3 O 4 was observed in the XRD investigation for the 10% mol Co-Ag sample in synthetic air.…”