Controlled Oxidation of Cobalt Nanoparticles to Obtain Co/CoO/Co3O4 Composites with Different Co Content

Abstract

The paper studies patterns of interaction of electroexplosive Co nanoparticles with air oxygen during heating. The characteristics of Co nanoparticles and composite Co/CoO/Co3O4 nanoparticles formed as a result of oxidation were studied using transmission electron microscopy, X-ray phase analysis, thermogravimetric analysis, differential scanning calorimetry, and vibrating sample magnetometry. It was established that nanoparticles with similar morphology in the form of hollow spheres with different content of Co, CoO, and Co3O4 can be produced by varying oxidation temperatures. The influence of the composition of composite nanoparticles on their magnetic characteristics is shown.

Novel Catalyst Composites of Ni- and Co-Based Nanoparticles Supported on Inorganic Oxides for Fatty Acid Hydrogenations

“…Moreover, NiCoNP@MgAl 2 O 4 and NiCoNP@TiO 2 presented lower M s values (156.2 and 52.0 emu/gNiCo) than the value for Co-hcp (162 emu/g) [38]. The lower value obtained for NiCoNP@TiO 2 in comparison to the Ni reference (54 emu/g for bulk Ni) could be due to the presence of nickel and cobalt oxides or the presence of capping agents, such as quinidine [39][40][41][42].…”

“…Significantly, the Ni 2p XPS core level spectra showed three contributions from Ni metal (17%), NiO (53%), and Ni(OH) 2 (50%), and the Co 2p XPS core level spectra showed three contributions from Co metal (16%), CoO (40%), and Co(OH) 2 (44%) (see Figure S18 and Table S2 in the Supplementary Materials). Despite the fact that Co 3 O 4 is thermodynamically more stable than CoO, the coexistence of Co(II) and Co(III) species is difficult to assess given their close binding energies (779.5 and 781.3 eV, respectively) [39][40][41][42]45]. However, a better fitting of the Co 2p 3/2 XPS core level spectra with the envelopes corresponding to Co 2p 3/2 peaks of the following references Co(0), Co 3 O 4 , CoO, Co(OH) 2 was obtained with a slight constraint on the position of each, where the presence of Co 3 O 4 fell to zero.…”

Selective Catalytic Hydrogenation of Fatty Acids with Cobalt–Halloysite Nanocomposites for Waste Valorization

“…CoA and CoB exhibited hysteresis with coercive fields of 445 and 469 Oe, and saturation magnetization ( M s ) of 102.2 and 66.8 emu/g respectively, showing a weak ferromagnetic behavior (see Figure S11a,b in the Supporting Information). The values of M s were lower than that reported for bulk Co- hcp (162 emu/g), probably due to either the presence of stabilizers over the surface of cobalt nanoparticles triggering surface spin capping effects , or the presence of cobalt oxides for CoA and CoB . − Moreover, CoC exhibited higher coercive field (1235 Oe) and higher saturation magnetization (248 emu/g) than CoA and CoB (see Figure S11c in the Supporting Information), evidencing a less saturated surface (absence of stabilizers in agreement with the behavior reported for cobalt clusters and nanoparticles). , …”

Preparation of a Robust and Highly Active Nonmagnetic Impregnated Cobalt/Carbon-Based Electrocatalyst for Hydrogen Production from the Electrolysis of Seawater

“…The ideal nucleation and nanoparticle growth are responsible for the creation of magnetism in the as-prepared sample. In this case, the antiferromagnetic characteristic of the prepared CoO/C electrocatalyst is clear due to the favor of the nucleation over the growth of nanoparticles, which provides the bigger particle size and low saturation value. , …”